# List of Scientific Instruments and Their Uses

## 1) Altimeter:

It is also known as altitude meter. It is used to measure the altitude or distance of an object above a fixed level such as the earth' surface, water surface, etc. For example, it can measure the altitude of an airplane, spacecraft, etc., from the earth or sea surface.

Altimeter can be of two types:

Pressure altimeter or aneroid barometer: It measures the location's altitude or distance above a fixed surface by calculating the air pressure of the object that can be an airplane or a hot air balloon or any other object flying in the sky. It works on the fact that the air pressure tends to decrease with an increase in the altitude. So, lower the pressure the more will be the altitude of the object. Pressure altimeter was invented by German engineer Paul Kollsman in the 1920s.

Radio altimeter: It measures the altitude or distance above land or water surface by using radio waves' signals. For example, it sends the radio waves from the object in the air to the ground, then measures the time taken by the radio waves to travel from the object to the ground and to return from the ground to the object. The more is the time taken, the more will be the altitude. The first radio altimeter was invented by Lloyd Espenschied in 1924.

## 2) Ammeter:

This scientific instrument is used to measure the electric current. The electric current is a flow of electrons that is measured in ampere. So, it is the instrument that measures the current in ampere, so it is called an ammeter or ampere meter.

### Types of Ammeter based on constructing principle:

• Permanent Magnet Moving Coil (PMMC) ammeter
• Moving Iron (MI) ammeter
• Electrodynamometer type ammeter
• Rectifier type ammeter

### Based on the type of measurement we do, there are two types:

• DC ammeter
• AC ammeter

Permanent Magnet Moving Coil (PMMC) ammeter: It has a coil located between the poles of a magnet. When the current is passed through the coil, the coil starts deflecting. The more is the current passing through the coil, more will be the deflection. It measures only the direct current (DC).

Moving Iron ammeter (MI): It can measure both alternating and direct current. The coil between the poles of a permanent magnet moves freely when the current is passed and deflects at a certain angle. The defection is directly proportional to the amount of current passed through the coil.

It has an iron piece that is attracted towards the coil when the current is passed through the coil due to the magnetic field created on passing the current through the coil. The iron piece when attracted creates a deflecting torque that causes the pointer to move over the scale.

Electro-dynamometer ammeter: It is also capable of measuring both AC and DC. The main advantage of using this ammeter is that it has the same calibration for both AC and DC.

Rectifier Ammeter: It measures only alternating current. It uses a moving coil and a rectifier to measure the current. It first rectifies the A.C to D.C then measures it. The scale is calibrated for measuring A.C.

## 3) Anemometer:

It is used to measure the speed, direction and pressure of wind in the atmosphere, in wind tunnels, houses, and more. It is provided with a spinning wheel. The stronger the wind blows, the faster the wheel rotates. The instrument counts the number of rotations and based on the count of rotations it calculates the wind speed. It is widely used by meteorologists to study weather patterns, and by physicists to study the movement of air.

The commonly used anemometer is made of three to four cups connected to horizontal rods. These rods are attached to a vertical rod. The cups starts rotating when the wind blows that makes the vertical rod spin. The faster the wind blows, the faster the rod spins.

## 4) Audiometer:

It is designed to measure the intensity of sound while evaluating hearing acuity. It is widely used by audiologists and other trained medical practitioners to check the hearing threshold of a person and to identify and quantify the degree of hearing loss in a person. From the findings and readings obtained using this device, appropriate medical treatment and hearing aid fitting can be prescribed.

The device generally comprises a hardware unit connected to headphones and a feedback button. These instruments are commonly found in ENT (ear, nose, and throat) clinics and other audiology centres.

## 5) Barometer:

It measures the atmospheric pressure, the pressure exerted by the air on the Earth's surface. Our atmosphere comprises different layers of air wrapped around the Earth. Due to gravitational pull towards Earth, the air presses against everything it touches, this pressure of air is called atmospheric pressure and is measured by a barometer. Atmospheric pressure changes with distance above or below sea level.

There are basically two types of barometers:

Mercury Barometer: It was invented in the 1640s by Evangelista Torricelli, an Italian physicist. So, sometimes it is also known as Torricellian barometer. It comprises an inverted glass tube standing upside down in a container filled with mercury. The glass tube is filled with mercury before placing it upside down in the container of mercury. The mercury level in the tube falls that creates a vacuum at the top. The level of mercury in the tube changes in response to the atmospheric pressure; the weight or pressure of the air in the atmosphere applied by the air on the mercury's surface in the container. If the mercury's weight in the tube is less than the pressure exerted by the air on the mercury in the container, the mercury's level in the tube tends to rise that indicates high atmospheric pressure. On the contrary, if the level of mercury falls, there will be low atmospheric pressure.

Aneroid Barometer: It is an alternative to liquid barometer as mercury is a poisonous liquid metal. It was invented by a French scientist Lucien Vidi in 1884. It looks like a clock or compass that contains a flexible metal box with air pumped out of it. So, a slight change in the external atmospheric pressure causes the metal box to expand and contract. The expansion and contraction of the metal box move the needle up or down around the barometer's face dial that indicates the change in pressure that helps find out the atmospheric pressure. In modern times, we use digital barometers that display reading on the screen.

## 6) Electron microscope:

It is used to see extremely small objects such as atoms, bacteria or viruses. It uses electrons to create an image of an object or specimen under observation. Its magnification or resolving power is very high as compared to ordinary microscopes. The electron microscopes can magnify an object up to two million times as compared to a light microscope which can magnify only up to 2000 times. The first electron microscope was invented in 1931 by German engineers Max Knoll and Ernst Ruska.

### What is the reason for the high resolution and magnification power of an electron microscope?

The electron microscope uses a beam of electrons to illuminate an object instead of a beam of light as used by a light microscope. The wavelength of an electron is much smaller than that of a light photon, and electromagnetic radiations, etc. The small wavelength helps produce a more enlarged view of a specimen. Besides this, an electron microscope, the image is formed by using electrostatic and electromagnetic lenses that control and focus the electron beam at a specific plane relative to the object. In a light microscope, glass lenses are used to focus light on the object to form an image.

## 7) Endoscope:

This instrument is used to examine or view the internal organs inside our body without performing surgery. It is a long, thin tube which is flexible enough to move inside our body. It has a light and a camera that allows us to see the inside of our body on a television screen. It is used to examine organs such as throat, oesophagus, stomach, etc.

It can be inserted into the body through mouth, anus or through a small cut made in the skin during keyhole surgery. Besides this, an endoscope is also used to take a biopsy (removal of tissue) to examine a disease.

An endoscope can be of different types based on the organ it views inside the body, such as:

• Colonoscope: It is used to examine the colon, so it is inserted through the anus.
• Bronchoscope: It is inserted through the mouth down the trachea or windpipe to view and examine the lungs.
• Gastroscope: It is used to examine the stomach and is inserted through the mouth down the oesophagus or food pipe.
• Hysteroscope: It is designed to examine the uterus. It enters the body through the cervix.
• Duodenoscope: It is used to examine and perform treatment on the pancreatic duct or bile duct. It enters the body through the stomach.
• Cystoscope and ureteroscope: It enters the body through the urethra. It is used to examine or inspect the ureters and the urinary bladder.

## 8) Fathometer:

It is a scientific instrument that is used to measure the depth of water, e.g. ocean depth. It is mostly used by ships to find out the depth of water below the ships. Fathometer is an echo-sounding instrument that uses sound waves to calculate the depth of water. It sends the sound waves to the ocean's floor then calculates the time taken by the sound waves to reach the ocean's floor and return back to the source. The main components of a fathometer include a transmitting and receiving oscillators, recorder unit and a power unit. The first practical fathometer was invented by Herbert Grove Dorsey, an American engineer.

The first fathometer was developed by a Bostan based company submarine signal in 1925. It was called the 312 fathometer. It was used to chart the depth of water while a ship was moving. It was more precise and easier to use than other instruments based on sounding methods. So, it became an important tool for the survey of oceans.

## 9) Galvanometer:

It is used to detect or measure the presence of small electric current and voltage. It also detects the direction of the current flowing in the circuit and the null point of the circuit. The null point refers to the time when no current is flowing in the circuit. It also tells about the voltage between any two points of the circuit. The first galvanometer was invented by Johann Schweigger in 1820.

The main components of a galvanometer include a moving coil, suspension, and permanent magnet. It works on the principle of conversion of electrical energy into mechanical energy. The presence of current in a magnetic field generates a magnetic torque and the coil turn by an angle which is directly proportional to the flow of current. The movement of the coil in a magnetic field indicates the presence of the current and its intensity. So, its main function is to detect the presence, direction of flow and the intensity of current in a conductor.

## 10) Hydrometer:

It is a scientific instrument that is designed to measure the relative density or specific gravity of different types of liquids. This instrument is a sealed glass tube which has a wider bottom portion that contains a heavy ballast such as lead or mercury for stability or to make the hydrometer float upright. The narrow upper stem is calibrated to take the measurements.

The liquid whose specific density is to be measured is poured into a tall container, then the hygrometer is gently dipped into the liquid and allowed to float freely. Hydrometer has a scale inside the stem so that reading can be taken directly. Calibrations on the tube stem correlate to the liquid's relative density. So, the reading on the calibrated stem that is touched by the surface of the liquid is noted down.

This instrument works on the Archimedes' principle which says that the buoyant force exerted by the water on a submerged object is equal to the weight of the water displaced by the submerged portion of the object. They are mostly used by winemakers to test the sugar content of wine and by the scientists for soil analysis.

## 11) Hydrophone:

This scientific instrument is an underwater device designed to detect, monitor and record underwater sounds coming from different directions. Just like a microphone receives sounds in the air, it receives acoustic signals in the water.

Sound is like a pressure wave that can move particles physically. So, the sound produces a mechanical force when it touches a hydrophone. The hydrophone converts a sound wave or acoustic energy into electrical energy based on the changes detected in the pressure in the surrounding environment. It just listens to the sounds in the sea but does not transmit any sound.

A hydrophone has a piezoelectric material that can be a piezoelectric transducer that is a device that produces an electric current when a mechanical force is applied to it.

A piezoelectric material can change its shape and convert the remaining mechanical energy into electrical energy. These days, the hydrophones are mostly used for listening to the sounds of underwater life and natural phenomena such as waves, earthquakes, and underwater volcanic eruptions. Besides this, it can also be used for underwater mapping, underwater communication and navigation.

## 12) Hygrometer:

It is used as a weather instrument as it is designed to measure the humidity in the air or atmosphere. Humidity is the amount of water vapour present in the atmosphere. The uncomfortable sticky feeling in summers is due to the high humidity in the air. Different types of hygrometers have been developed over the centuries. The most commonly used hygrometer is called a psychrometer. It is provided with two mercury thermometers one has a dry bulb and another one with a wet bulb. Horace Benedict de Saussure had designed one of the first hydrometers in 1783.

The evaporation takes place in the web bulb that decreases its temperature, which causes it to show a lower temperature than the dry bulb. Thereafter, the relative humidity is calculated by comparing the ambient temperature (the surrounding's temperature or dry bulb's temperature) to the difference between the temperatures of the two thermometers. This type of hygrometers is suitable for measuring humidity in the outdoor areas and indoor places such as storage areas where dry conditions need to be maintained.

## 13) Hypsometer:

It is used to measure the height or elevation of an object such as a building, tree, etc. A hypsometer can be of different types based on the principles it uses to measure the height. Such as scale hypsometer that uses trigonometry and pressure hypsometer that uses the concept of atmospheric pressure. It is most often used for survey and by the construction industries to measure the height of buildings and by arborists to measure the heights of trees.

### Types of hypsometer:

Scale hypsometer: It is the simplest type of hypsometer that comprises L-shaped frame and an adjustable straightedge. The top of the object is seen using the straightedge that makes an angle between the bottom of the frame and the straightedge. With the help of this angle and formula of trigonometry, the height of the object can be calculated.

Pressure hypsometer: It is based on the principle that the boiling point of a liquid tends to decrease with an increase in height. It comprises a container filled with water, a heating mechanism, and a thermometer. The temperature at which water boils is compared to a data table to find out the height of the object.

Laser hypsometer: As the name suggests, these hypsometers use the laser to measure the height of objects. Laser hypsometer is typically used by arborists to measure the height of trees. It uses a combination of laser, ultrasound, and tilt sensor to calculate the height, distance and angle related to the object.

## 14) Machmeter:

It is a scientific instrument that measures the ratio of the speed of the aircraft to the speed of the sound, this ratio is called Mach Number (M). When M is equal to one, the speed of the aircraft is equal to the speed of the sound. This instrument is very important for the aircraft that fly at high speed. The pilot can easily understand whether he is flying within the safe speed limits or not.

The formula for the calculation the Mach number is given below:

Mach = TAS/LSS

Where TAS stands for a true airspeed of the aircraft

And, LSS stands for the local speed of sound.

So, if the Mach number is 2, that means the given airplane is flying at double the speed of the sound.

## 15) Odometer:

It is a scientific instrument that indicates the distance travelled by a vehicle such as a car, motorcycle, etc. It can a mechanical or electronic device or a combination of both, e.g., electromechanical odometer. It is generally located in the dashboard of a vehicle.

A mechanical odometer has a series of cogs. Each cog represents a number. The cogs turn in coordination with the rotation of the wheel. There is a single row of numbers that keeps changing as the vehicle keeps travelling to show the distance covered by the vehicle.

The advanced electronic or digital odometer is provided with a computer chip to measure the distance covered. The readings are displayed digitally. A prototype odometer was built by Benjamin Franklin in 1775, to measure the mileage of his carriage.

## 16) Ohmmeter:

It is used to measure or calculate the electrical resistance of a circuit. The unit of resistance is ohm, so it is measured in ohm. The electrical resistance of a circuit or conductor indicates how much it resists the flow of current through it.

An ohmmeter can be of different types based on their sensitivity levels, such as:

Micro-ohmmeters: They are used to measure very low resistances with high precision.

Mega-ohmmeter: It is used for measuring the high resistances of the electric circuits.

Milli-ohmmeter: It is used for measuring low-resistance at high precision to check the value of an electrical circuit.

Based on the arrangement there are two types of ohmmeters:

• Series type ohmmeter: In this type of ohmmeter, the resistor whose resistance is to be measured is placed in series with the ohmmeter. In this case, the ohmmeter is called a series ohmmeter.
• Shunt type ohmmeter: In this type of ohmmeter, the resistor whose resistance is to be measured is placed in parallel with the ohmmeter. In this case, the ohmmeter is called a shunt ohmmeter. It is suitable for measuring low-value resistance.

## 17) Cathetometer:

It is a scientific instrument which is used to measure the minute differences in the levels of surfaces of liquids with great accuracy. E.g., the distance between the levels of the mercury in the tube of a barometer and in any other container such as a cistern, glass tube, etc.

It is used in cases where a scale cannot be placed very close to the points whose vertical levels' difference is to be calculated. For example, the difference in the heights of the upper surfaces of two columns one with mercury and another one with any other liquid, or the same liquid in two columns at different times.

The instrument is made up of a horizontal telescopic mounted on a vertical column in such a way that it can be moved up or down the vertical column while measuring the levels. It also has an accurately calibrated scale to read the position of the telescope. Before taking the readings, the instrument should be levelled, then the cross-hair in the telescope's eyepiece is made to coincide with the image of one point and reading is noted down, similarly, it coincides again with the image of other point or surface and reading is taken. Then the difference between these two readings is calculated which is the required difference in the levels of surfaces.

Cathetometer can be used to measure levels of liquids in the same tube at different times such as to measure the surface tension of a liquid contained in a capillary tube. It can also be used to check the difference in the levels of a liquid in dilatometer due to a chemical reaction.

## 18) Colorimeter:

Calorimeter is used to measure the absorbency of light waves. It is a light-sensitive device that is used for measuring the absorbance of light passing through a liquid sample. Absorbance is the amount of light absorbed by a solution containing a solute.

This measurement helps find the concentration of substances or a known solute in a given solution as the amount of the light absorbed depends on the concentration of the solute in a given solution by using the Beer's law. This law states that the amount of the light absorbed by the solute in a solution is directly proportional to the concentration of the solute, which means more is the solute, more light is absorbed.

The parts of a colorimeter include a light source, a cuvette that contains the sample, and a photocell to detect the light. Using a colorimeter, the amount of light travelling through a solution is compared with the amount of light that can get through a sample of pure solvent that does not contain the solute. The difference between the amount of light at the beginning and after passing the solution is measured.

Before using the colorimeter, several sample solutions of a known concentration are first prepared and tested. Then a graph is created of the known concentrations against absorbance and thus a calibration curve is generated. Then results or absorbance of the unknown sample is compared to that of the known sample on the curve to measure the concentration.

A colorimeter is generally provided with a photocell that can detect the amount of light passing through the given solution. The photocell produces a current that depends on the quantity of light that hits it after passing through the coloured solution. Less current will be produced if less light passes through the solution.

## 19) Crescograph:

It is a device that is used to measure the growth in plants. It was invented by Sir Jagadish Chandra Bose at the beginning of the 20th century. This main components of this instrument include a smoked glass plate and clockwise gears. The plate is calibrated at regular distance intervals to measure the growth or movement of the tip or roots of a plant under observation at a magnification of up to 10,000 times. And, the role of clockwise gears is to measure the influence on growth under different circumstances, under varying stimuli such as temperature, gases, chemicals, electricity.

Inspired from the Bose's crescograph, a modern electronic crescograph was developed by Randall Fontes to measure movement in plants at Stanford Research Institute with a normal operating range of 1/1000 to 1/10,000 of an inch.

## 20) Cryometer:

It is a type of thermometer that is used to measure very low temperatures of objects. There are lots of devices that can be used as Cryometers. These devices are mostly used to measure low temperature in space. For example:

• Thermocouple: It can measure the low temperature around 1K.
• Vapour pressure thermometers: It can measure temperature as low as 0.5K.
• Resistance thermometer: It can measure temperature as low as 0.01K.
• Melting curve thermometer: It can measure between 0.5K and 0.001K.
• Resistance noise thermometer: It measures around 0.001K.
• Magnetic thermometers: It is suitable to be used at 0.001K.
• Nuclear-resonance thermometers: They are used to measure low temperatures that can be as low as 0.0000001K.

## 21) Dilatometer:

It is a scientific instrument that is developed to measure the changes in the volume or length of a material that occurs as a result of a change in temperature. These materials can be ceramics, glasses, polymers, and metals. These changes in the dimension of material are measured on the basis of dilatometry. There can be many reasons for volume changes apart from temperature such as absorption of fluids, chemical reactions, or mechanical stress such as pressure on a solid object.

A dilatometer is typically a complex scientific instrument. However, dilatometers with simple mechanism are also available. Some of the common types of dilatometers are as follows:

• Flat plate dilatometer: It is also known as capacity dilatometer. It is made up of two plates; one plate can move, whereas another one remains fixed. It is particularly used for detecting changes in the volume of solids. A thin piece of material to be measured is inserted into the slot of the device. It expands when the temperature is increased and due to this expansion, the movable plate is pushed, which is connected to a computer that can measure even small movements.
• Connecting rod dilatometer: It is also known as push rod dilatometer. It is designed to measure the changes in dimension of a material when it is heated. The change in the volume of the material is measured relative to the change in the volume of the rod of the instrument. The instrument's rod is a control specimen with a known expansion coefficient. So, by comparing the expansion of test specimen with the expansion of the rod, the user can calculate the expansion of the specimen undergoing the test.
• Laser dilatometer: It can measure tiny changes in dimensions. It generally works by striking the laser light on the test material and there is a laser receptor to measure minute changes in the diameter of the resulting shadow.
• Optical dilatometer: It is provided with a digital camera to detect small changes in the dimensions of the test material.

## 22) Electroscope:

It is an instrument used to detect the presence of an electric charge on a body. The first electroscope was developed by a British physician William Gilbert in 1600. It had a pivoted needle and was called versorium.

It works on the principle of Coulomb electrostatic force and is comprised of a metal detector knob which is connected to a pair of metal leaves. In the absence of the charge in the test object, the metal leaves hang loosely towards the ground or downward. Whereas, when a charged object is brought near an electroscope you may notice the following changes or reactions.

In case of a positive charge in the object, the electrons in the electroscope's metal get attracted to the charge and move upward out of the leaves that tend to build a temporary positive charge in the leaves and as the same charges tend to repel each other, the leaves get separated. On removing the charge, the electrons take their original position and the leaves also come to their initial position.

In case the charge on the test object is negative, the electrons in the metal of the electroscope repel and move toward the bottom of the leaves. This increases the negative charge in the leaves temporarily again as same charges repel, the leaves will separate again.

In both cases, the leaves move away from each other, so it should be noted that the electroscope cannot tell whether the charged test object is carrying a positive charge or negative charge. It can only be used to detect the presence of an electrical charge.

### Types of electroscope:

The two standard types of electroscope are described below:

Pith-ball electroscope:

It was invented in 1754 by John Canton. It comprises of one or two small light balls made of non-conductive light-weight material called pith. The test object is brought close to the pith-ball to detect the presence of charge on it. If the ball moves towards or away from the object, the object is charged and vice versa.

Gold-leaf electroscope:

It was developed in 1787 by Abraham Bennet. It was more sensitive as compared to the pith-ball electroscope. It is made of a vertical metal rod fitted in a glass bottle. The rod is provided with two parallel, thin and flexible strips of gold at the bottom end. It is kept in a glass bottle to prevent the movement of gold leaf due to the effect of air. When a charged object comes close to the leaves, the leaves move apart and looks like inverted "V", as shown in the above image.

## 23) Ondometer:

It is used to measure the wavelength and nature of the electromagnetic radiations or waves. It is sometimes also called wavemeter. The electromagnetic radiation is comprised of many radiations of different wavelengths known as the electromagnetic spectrum. The radio waves are known to have the highest wavelength and gamma rays are known to have the shortest wavelength. So, ondometer is designed to distinguish the radiations on the basis of their wavelengths.

## 24) Optometer:

It is a device that tracks the path travelled by the light after it enters the eye. It is called eye refraction. If the path travelled by light is not normal then it is known as a refractive error that may be corrected using eyeglasses or contact lenses. The word Optometer is derived from two Greek words "optikos" which means "sight," and "metron" which means "measure".

Thus, Optometer helps assess a patient' vision by providing numbers as per the power of a person's vision. It is widely used by optometrist or ophthalmologist in a clinical setting.

For determining appropriate lens prescription. The eye specialist needs to be very careful while generating the number using this device as a lens of wrong power can further deteriorate the patients' vision. The use of Optometer is called optometry.

## 25) Otoscope:

It is a specialized hand-held instrument used by physicians to examine the ear more specifically the ear canal and eardrum. Its name is derived from two words "Oto" means Ear and "scope" means to view. However, it can also be used to examine the nose and throat passages in the body.

While using the otoscope, the ear lobe is held by one hand before inserting the speculum into the ear and the otoscope's position can be adjusted to get a better view of the internal parts of the ear.

Both hands remain busy while using this device; one hand holds the ear and with other hand otoscope is hold. It generally consists of a head, a magnifier, a light and a handle to hold the device. Its tip can be manipulated or adjusted to view different parts of the ear and nasal passages from different angles.

Some otoscope can perform some specialized functions such as pneumatic otoscopes that send a small puff of air to the eardrum to check the vibration produced in the eardrum. It detects wax build-up in the ear canal or a rupture in the eardrum.

## 26) Periscope:

It is a device that is designed to observe over, or around an obstacle that prevents the direct line of sight. It works on the principle of laws of reflection of light. So, an object that is placed in the line of sight reflects the light towards the eyepiece making the target visible in the periscope.

It consists of an outer body provided with two mirrors at an angle of 45 degrees to each other so that when light falls on one mirror, it is reflected back and falls on the other mirror and gets reflected again towards the observer's eyes.

It is mostly used in land and sea warfare, submarine navigation. It allows the user to see the surroundings while remaining hidden, undercover, or behind armour or submerged in the water.

## 27) Phonograph:

It is a device that is developed to reproduce the sound recorded on a grooved disc. It is provided with a stylus or needle that vibrates while following a spiral groove on the revolving disc to reproduce sound. It is also known as a gramophone or disc player or a record player.

The sound is recorded in a phonographic disc in a sinuous groove carved on its rotating surface as a series of ripples by the stylus. When the recording is played back using a phonograph the pen responds to the ripples to reproduce the sound. It works smoothly and is capable of producing a clean and high sound. The phonograph was invented on 21 November 1877 by Thomas Alva Edison and he got it patented on 19 February 1878.

## 28) Polygraph:

It is sometimes known as a lie-detector device. It is typically used to test the physiological responses of a person while replying to a set of yes or no questions related to a crime, incident, and any other sensitive purpose. Its objective is to check if a person is telling the truth or lying while answering a set of questions. It is also performed on a person applying for certain government jobs such as while applying for a job in the FBI or CIA.

While performing this test, four to six sensors are placed on different points on the body of the person. Thereafter, signals provided by the sensors are recorded on a strip of moving paper in the form a graph. It usually records the following physiological responses or signals produced by the person's body:

• Breathing rate
• Pulse rate
• Blood pressure
• Perspiration

Besides the above symptoms, sometimes it can also record other signals like arm and leg movement. If it deviates too much from the normal reading after an answer, the examiner makes a note of it.

## 29) Pyrometer:

It is a scientific device that is designed to measure relatively high temperature such as in furnaces without touching and where we cannot use ordinary thermometers. It is based on the fact that every hot object emits heat or thermal radiations. So, most of the pyrometers work by measuring heat radiations emitted from the objects.

The device picks up thermal radiations then analyses and measures them and based on its analysis provides the temperature measurement of the object. More the radiations produced by a substance more is the temperature of the substance.

The basic design or components of a pyrometer include an optical system and detectors. The optical system made of the lens focuses on the heat radiations emitted by the object and collects the radiations then sends them to the photodetector, which is sensitive to radiations. The detector then analyses the energy level of the radiation and accordingly provides the output about the temperature of the object. The detector transforms the heat radiations into electrical signals which are processed and changed into an output signal that appears on the display as a reading for the object's temperature. The first pyrometer device was invented by Josiah Wedgwood.

It stands for Radio Detection and Ranging. As the name suggests, it is a detection system that is used to determine the location and distance of distant objects using radio waves. A standard radar system consists of an antenna to transmit the radio signal or electromagnetic waves in a particular direction and a receiver that detects and receives the echoes that are reflected from the target object that comes in the path of the radio signal. Based on the analysis of echoes received, the position, location, distance and speed of the target object are calculated.

The distance of the target object from the radar is determined by calculating the time taken by the waves to hit the target and return back as an echo to the receiver. The Radar system was developed secretly during the period of World War II by different countries. The term RADAR was used for the first time by the US Navy in 1940.

It provides the following information:

• The angle and direction of movement of the object.
• The distance that tells how far is the object from the radar.
• The relative movement between the object and the transmitter.
• The speed and distance travelled by the object can be calculated by combining together different measurements or pulses.
• The radar with high-resolution power can even identify the shape of the object such as airplane type, missile type, etc.

Radar can be used for various purposes, some of which are as follows:

• To track and detect the position or presence of satellites, spacecraft, planets, and other celestial bodies.
• To navigate aircraft in the sky and ships in the water.
• To control and manage the traffic in the air.
• To find out the location of the fighter jets, helicopters, etc., of the enemy.

## 31) Rain Gauge:

It is a simple scientific instrument that is used to measure the amount of rain during a particular interval of time per unit area. It is also known as ombrometer.

The first standard rain gauge was invented in Korea in 1441. Later, in 1661, Christopher Wren and Robert Hooke developed the first tipping bucket rain gauge in Britain.

A standard Rain Gauge (Cylinder Ombrometer) is comprised of a graduated cylinder that is placed in an open area to collect the rainwater. During the rainfall, the water gets collected in the cylinder. By noticing the level of water in the calibrated cylinder you can measure the total rainfall. For example, if water level touches one-inch mark that means one inch of rain fell on the ground in that place.

A rain gauge may have two cylinders; a small cylinder placed inside the larger cylinder. So, if the smaller one fills up, the extra rainwater will be collected in the larger one and can be used to measure the total rainfall accurately.

### Types of Rain Gauge:

Apart from the standard rain gauge, there are many types of rain gauges such as:

• Symons Rain Gauge
• Tipping bucket
• Weighing bucket

## 32) Refractometer:

It is a scientific instrument that is used to measure the refractive index of a liquid or solid substance. It measures how much the light bents or refracted when it enters into a substance from the air. It is based on the fact that light travels at different velocities in different mediums such as solids, liquids, gases, etc.

It measures the characteristics of liquids and solids using the light refraction. When it is used for liquids, it tells about their salinity, specific gravity and fluid concentration, etc. This device is used in multiple industries e.g., in the food and beverage industry by researchers and in the jewellery industry by gemmologist.

### Types of Refractometer:

• Handheld or portable refractometer: It can be a manual type or a digital type.
• Automatic refractometers: It takes automated measurements that tend to reduce operator errors and provide quick results and can be connected with other instruments such as pH meters, density meters, etc.
• Benchtop Abbe refractometer: It mostly used for solids testing and is known for its high accuracy.
• Inline process refractometer: It analyses the liquid flow through a pipe or tank and is provided with a sensor to measure and compare the solution to a control sample.

### Uses of Refractometer:

• Winemaking industry uses to measure the sugar content of grapes or other fruits.
• Sugar companies use it to find out the percentage of sugar in syrups, concentrated saps, etc.
• Doctors use them to determine the concentration of proteins in blood samples.
• It can be used to determine the salinity of a salt-water aquarium.
• It is also used to identify a sample by comparing its refractive index to the predefined refractive indexes of other substances.

## 33) Sextant:

It is used to find out the angle between the horizon and a celestial body such as Stars, Moon, Sun, etc. It is a navigation instrument that helps determine longitude and latitude, more specifically the altitude of the sun, stars above the horizon. So, it helps a navigator to find his position on the earth while travelling in a ship.

It has two mirrors, one is fixed on the sextant' body and the other one is fixed on the index arm called the pivot. The arrangement of the mirrors allows the observer to view both the objects at the same time.

It is based on the principle that when a ray of light gets reflected from two mirrors in the same plane, then the angle made between the incident and reflected ray of light is two times the angle between the mirrors.

The basic parts of a marine sextant are as follows:

• Regulation screw: It allows the user to adjust the horizon mirror.
• Triangular frame: It provides a frame to hold other parts of the instrument.
• Index mirror: It is present on the top of the frame attached to the index arm.
• Index arm: It can be moved or adjusted to take the correct reading of the altitude of the reference body.
• Telescope: It allows the user to see the magnified image of the object and to look at the horizon glass through the telescope.
• Eyepiece: It is the lens of the telescope through which the observer sees the object.
• Horizon Glass or mirror: It allows to view two objects at the same time. One object directly in the line of sight and another object that is reflected next to it from the index mirror. The half of the portion of horizon glass is silvered and remaining half portion is clear.
• Index Plate: It is a plate whose job is to reflect objects onto the horizon glass.
• Vernier Scale: It is a curved scale located beside the micrometre drum and is connected to the index arm to indicate the angle.
• Micrometre Drum: It is connected to the lower part of the index arm. It can be rotated to allow users to make adjustments while measuring angles.

The observer is required to position the sextant in a way that he or she could see the horizon through the clear part of the horizon glass while viewing it through the telescope. The movable index arm has the second mirror (index mirror) that receives the light from the celestial body. This arm is adjusted in a way that the image of the reference body such as sun appears in the horizon mirror touching the horizon. Now, the altitude of the body can be determined from the position of the arm along the Vernier scale.

## 34) Seismograph:

It is a scientific instrument developed to detect, measure or record earthquakes. It is capable of recording the motion of the ground during an earthquake. Sometimes, it is also called a seismometer. During an earthquake, seismic waves are produced. These propagating vibrations travel outward to all directions carrying energy from the origin of an earthquake. The record of vibrations produced by a seismograph on a screen or a paper is called a seismogram. Using a seismograph, you can find out, the magnitude, depth and location of the earthquake.

Chang Heng, a Chinese astronomer invented the first seismograph in 132 A.D. and named it "earthquake weathercock." Later in 136 A.D. a Chinese scientist Choke improved this meter and named it "seismoscope". In the modern world, the first seismograph was invented by John Milne in 1880.

The electronic seismometers that we use in modern times can detect and record motion in all directions. Besides this, this instrument can also be used to track large explosions, tidal waves, volcanoes, etc.

The basic seismograph consists of the following components:

• Base: It supports the frame and drum.
• Frame: It holds the mass, spring and vibrates during an earthquake.
• Mass or heavyweight: It hangs downward attached to frame with wire or spring.
• Pen: It creates patter or graph on the paper-covered drum.
• Rotation drum: It is covered with paper and rotates when the pen draws a pattern on it.

### How does seismograph work?

A seismograph is firmly mounted on the earth's surface so that when an earthquake comes or the earth vibrates the entire instrument starts shaking expect for the mass (heavyweight) that tends to remain stationary due to the inertia of rest.

The relative motion of the mass (weight) and the unit is used to measure the ground motion. The pen attached to mass draws the zigzag pattern on the rotating drum attached to the base. The pattern shows the changing amplitude of ground oscillations beneath the base.

In some instruments, the recording device on the mass records the relative motion between the mass and the instrument and converts it into an electrical signal which can be recorded on a paper, magnetic tape or any other recording medium.

The movement of ground moves the frame, but the mass tends to remain in rest because of the inertia of rest, the movement between the frame and mass is measured to determine the motion of the ground.

The seismogram is the recording of the vibrations produced due to the earthquake. It has a horizontal axis that denotes time measured in axis and vertical axis that indicates ground displacement in millimetres. During the absence of earthquake, the reading is just a straight line except for small wiggles due to local disturbances.

## 35) Speedometer:

It is a device installed in the vehicles to measure their speed while moving on the roads. It allows drivers to maintain a sensible and safe pace. It indicates the speed in miles per hour, kilometres per hour or both. Josip Belusic invented the first speedometer in 1888.

The driver cable starts the working of a speedometer. It provides the input to the speedometer. The one end of the cable is connected to the tyre whereas the other end is connected to the speedometer assembly. As the wheel moves, it also starts moving and transfers these rotations to the speedometer.

The first speedometer was invented by Charles Babbage, later the more advanced electric speedometer was invented by Croatian Josip Belusic in 1888, and it was called a velocimeter.

It can be of three types:

Mechanical speedometer: As the name suggests, it relies on the mechanical components such as shaft to get the signal for speed, and has permanent magnets and centrifugal device to know the power torque and maintain the balance with the spring's reaction torque.

Electronic speedometer: It is more advanced than mechanical ones. It was introduced after 1993. An electronic speedometer has an electronic speed sensors such as hall element to get speed signal and to access actuator through the circuit processing, and to make use of step motor needles directly.

Electrical speedometer: In this type of speedometers, generator connection with the output shaft of the transmission is used to get the speed signal, and to have access to the motor to get power moments and maintain balance with the spring's reaction torque.

## 36) Spherometer:

A Spherometer is a scientific device that is developed to measure the radius of curvature of spherical surfaces with great precision. The radius of curvature of a curved mirror is the radius of the sphere that was used to make the curved mirror.

For the first time, it was used by the opticians to measure the curvatures of the spherical surfaces of the lens. It is placed on the mirror whose radius of curvature is to be measured. It was French optician Robert Aglae Cauchoix who discovered the first known Spherometer in 1810.

In general, it consists of the following components:

• Three outer legs that form a base circle of known radius. These legs lie on a flat surface.
• A central leg parallel to the three legs, which is a screw that can be screwed down to the touch the surface to obtain the zero reading.
• The head of the screw has a graduated disk that measures the small turns of the screw.
• The vertical scale called pitch scale is attached to one of the legs of the Spherometer. It measures the height or depth of the bend of the spherical surface. Pitch is the distance moved by the middle screw per revolution.

## 37) Sphygmomanometer:

It is used to measure blood pressure in humans.

It consists of the following parts:

• Cuff: It is a cloth-covered inflatable rubber bladder that is wrapped or placed around the arm.
• Measuring device: It is used to measure the cuff's pressure.
• A rubber bulb with valve: It is used to inflate the cuff as well as to releases the pressure.

The blood pressure reading obtained by using a sphygmomanometer is composed of two numbers that indicate systolic and diastolic pressures. E.g. 120/80 mm Hg.

The top number indicates the systolic pressure in your arteries when your heart muscle contracts. Diastolic refers to the resting period between two heartbeats. The contractions and relaxations of hear muscles cause heartbeats that pushes blood into the arteries. It causes a rise (during contractions) and a fall (during relaxations) in arterial blood pressure. The highest arterial pressure during contractions is called systolic pressure and it is followed by low blood pressure during the relaxation phase, which is called diastolic pressure.

### How sphygmomanometer works:

The cuff is wrapped around the upper arm of the person. Then it is filled with air by using a rubber bulb. It is inflated until the artery is completely blocked or blood flow is restricted completely. Then the air pressure is released slowly and while releasing this pressure the arterial blood blow sounds are listened using a stethoscope. A point comes when the blocked artery starts with blood flow; a pounding or whooshing sound is heard at this point and this pressure at which it happens it noted and recorded as the systolic blood pressure (the top reading of the blood pressure).

The pressure is released further until the examiner stops hearing the sound. The point at which sound can no longer be heard is recorded as the diastolic blood pressure.

The level of mercury is observed in the column while pressure is released gradually to read the values of the blood pressure. The highest pressure in the arteries during the cardiac cycle is the systolic pressure and the lowest pressure at the resting phase of the cardiac cycle is the diastolic pressure. High blood pressure indicates that the heart is working hard to pump out blood to different parts of the body.

## 38) Stethoscope:

It is a scientific instrument that is used by doctors to detect or listen to the sounds produced in the body such as heartbeats and sounds produced in lungs, intestinal tract including the sound of blood flow in the peripheral vessels and the heart sounds of the foetus in the womb of pregnant women. It is used for the proper diagnosis of a patient's condition or illness. It is a binaural device, so it is used with both the ears.

The stethoscope is most often used to detect the heart murmurs or abnormal heartbeats, and to listen to the sound of air moving through the lungs to detect abnormalities in the air tubes and air passages in the lungs. It was invented by French physician R.T.H. Laennec in 1819. In general, a stethoscope consists of the following components:

• Earpieces: There are two earpieces or Eartips that enters into ears while hearing the sound. It receives the sound send by the chest-piece. The anatomically correct position of earpieces allows a proper fit into ear canals.
• Eartube: It is the metal part of the device that connects the rubber tube with the earpieces.
• Rubber tube or tubing: It is the flexible part of the device that transfers the sound from the chest piece to eartubes.
• Stem: It is a steel part of the device that connects the tubing to the chest piece. It also allows the user to change the diaphragm and bell sides of the chest-piece by turning the chest piece.
• Head or Chest piece: It is placed against a patient's body. It can be single-sided where it will have a diaphragm or a bell. However, the double-sided stethoscopes have diaphragm on one side and bell on the opposite side.

## 39) Tachometer:

It is used to measure the rotation speed of a rotating object such as crankshaft of an engine. It measures revolutions per minute performed by the object. A tachometer is also known as a revolution counter. In general, it comprises a dial and a needle to display the readings related to safe and dangerous limits.

An engine is designed to spin within its limits or as per the piston's ability to pump the crankshaft to spin. The tachometer counts the number of revolutions the crankshaft is making in a minute. If the RPM is more than the allowed range, the moving parts will produce heat and friction and will get damaged. So, a tachometer has been provided to let the driver known the safe speed limits. There are various types of tachometers used in vehicles. Such as:

Analog tachometers: As the name suggests, it comprises a needle and dial-type interface. It cannot store readings. It converts the speed to voltage using external frequency and voltage converter. After the conversion, the voltage is displayed by the analogue voltmeter.

Working: The engine's speed is converted into a voltage which is transferred to the moving coil. It causes the production of the magnetic field by the coil which tends to align itself with the magnetic field of the magnets. In doing so, the coil moves against the spring which results in the deflection of the needle.

Digital tachometers: They have a digital display unit and also a memory for storing the information. It works on the principle of generator which means motor behaves like a generator, it generates a voltage as per the velocity of the shaft. Besides this, it is also capable of performing statistical functions like averaging.

Working: It is provided with an optical sensor that produces pulses. These pulses, which are directly proportional to the speed of rotation, are counted and total no. of pulses per second is determined. It provides the revolution per second which is multiplied by 60 to get RPM. It can measure as low as 0.5 rpm and as high as 1000 rpm.

A digital tachometer can be of two types:

Contact type: As the name suggests, it has direct physical contact with the rotating shaft. It is attached to the electric motor or machine and an optical encoder or magnetic sensor is attached to it in order to measure the RPM.

Non-contact type: It does not require any physical contact with the rotating shaft. The tachometer directs IR beam or laser on the rotating shaft to get the readings. It has an LCD display and it can measure from 1 to 99999 rpm.

## 40) Telemeter:

It is used to measure the distance between two objects, which may be moving or only one of them is moving and another one is stationary. It was developed for the first time by the army to find out the distance of enemy camps based on the sound made by their gunfire. Even today it is used in the military in combination with other technologies to find the range of enemy weapons and missiles. Besides these applications, it can also be used in prediction of weather conditions, tracking of bird and aquatic animals, exploring the space, and more.

Telemetry uses the trigonometry and mathematical calculations to provide the results. The early model of telemeter comprised of two attached telescopes, which were some distance apart but were focused on the same target. Then the relative distance between the telescopes and the target object is calculated through triangulation of the distance as a factor of the optical differential that separates the two telescopes.

However, in modern times, the advanced telemeters make use of the radar, GPS, and sound wave technologies to perform the calculations faster and quickly. Most of the telemeters may have an internal computer drive to calculate the distance based on the speed, map data, and bounce of the sound wave.

### Major uses of telemeter:

• The electronic telemeters help fighter jets to estimate the distance of the fire of enemies. It also helps to destroy the targets using missile lock-on; a process that acquires a target and tracts it to guide the missile to hit it accurately.
• It is used by space agencies to gather data and monitor satellite movements.
• It is used by the weather department to determine the time, speed and distance of storms.
• It is used by zoologists to track birds and sea creatures for analysing species and migratory data.

## 41) Thermometer:

It is a scientific device that is used to measure temperature. It can be of different types as it can be used to measure the temperature of a wide range of substances such as food, liquids, gases, air and human body temperature. The commonly used measurement units for the measurement of temperature include Kelvin, Fahrenheit and Celsius.

To measure the body temperature, we generally use either a liquid thermometer or a digital thermometer both are described as follows:

Liquid thermometer: It consists of a calibrated sealed tube that contains liquid, which is generally mercury. It is an analogue thermometer as it has markings on the tube. It measures body temperature in the range of 35 degrees centigrade to 42 degrees centigrade.

It works on the principle that says liquids tend to expand with an increase in temperature. So, as the temperature increases, the mercury in a thermometer expands and moves up the scale and stops moving after it has expanded completely in response to the temperature. This reading on the scale indicates the temperature.

For some years they are not in use as they contain mercury, which is highly poisonous. However, there is no danger as long as it is inside the tube, but if the tube happens to break someone may be exposed to this poisonous liquid. So, some liquid thermometers contain an alcohol-based liquid such as ethanol. It is safe as well as it can measure low temperatures as alcohol's freezing point is less than the mercury's freezing point.

Digital thermometers: As the name suggest, it has a digital panel to display the reading in the form of digits or numbers such as 98 degrees Fahrenheit. It is a compact device that is easy to use, store and carry and is more accurate. It can be used under the armpit in case of a child. It has an electronic circuit which captures the information and sends it to a microchip that processes the information and displays it on the digital panel.

Infrared thermometers: These thermometers can detect the temperature without touching the object. So, they are widely used while screening people for an infection such as in the case of coronavirus. They allow you to measure the temperature from a reasonable distance from a person.

They work by capturing the heat emitted from the body in the form of infrared energy. The temperature is calculated from the emission spectrum of the infrared waves emitted by an object without any direct contact.

### Uses of thermometers:

• It is used by doctors to check body temperature during fever or any other illness.
• It can be used in the kitchen to measure the temperature of foods.
• It is used in refrigerator and air conditioners to maintain a set temperature.
• In factories, it is used to turn on and off the furnace. You are required to choose the right type of thermometer that suits your requirements.

## 42) Tonometer:

Tonometer is used to measure the pressure inside the eyes of a person. This internal pressure of the eye is known as the intraocular pressure (IOP). Tonometry is a test that is performed using a tonometer for the diagnosis of glaucoma, a disease in which the fluid pressure inside the eye increases that may damage the optic nerve.

The Goldman applanation tonometer is the commonly used tonometer by the doctors. In Goldman tonometry, first anaesthetic eye drops are poured into the eyes then a small amount of a fluorescein dye. Then fluorescein and the tonometer are illuminated using a cobalt blue light. Thereafter a small pressure is applied onto the eye that tends to indent the cornea. As a reaction, the cornea pushes back onto the tonometer, which is measured to get the output. Some tonometers are very compact just like a writing pen that is gently applied on the cornea for a short duration.

In non-contact tonometry, non-contact tonometers are used that use a puff of air to measure IOP by flattening the cornea. Although it is painless, it produces sound when air puff is released.

## 43) Venturimeter:

It is a scientific device that is used to measure the speed and rate of flow of a fluid that is flowing in a pipe. It works on the principle of Bernoulli's equation that says as the velocity increases pressure decreases.

Although the principle of Venturimeter was introduced for the first time by G.D. Venturi in 1797, it was considered with the support of C. Herschel in 1887. This principle states that when the cross-sectional area of a pipe through which a liquid is flowing is reduced then a pressure difference is created between the different areas of flow which can be used to measure the difference in pressure.

A Venturimeter consists of the following three main components:

• Converging part: It is the starting part of the device whose radius or area of cross-section decreases as we move forward towards the middle portion of the device. So, the speed of the flow of water increases and pressure decreases.
• Throat: It is the central part of the device whose area of the cross-section remains the same so the speed of flowing water and pressure remains constant in this part of the Venturimeter.
• Diverging part: It is the part where the fluid is discharged. It allows the fluid to regain its pressure and kinetic energy.

A manometer is attached between the first part and the throat section of the device to record the pressure difference between the converging part and the throat. It indicates the flow rate of the fluid through the pipe based on the pressure difference.

### Working:

One end of the pipe is connected to the converging part and another part of the pipe is connected to the diverging part. The water enters the converging part then enters the throat. In the converging part due to the decreasing area the velocity increases and pressure decreases. Then water enters the throat whose area is uniform and least in the device. So, as the water enters the throat its velocity and pressure remain the same that causes pressure difference of the fluid at the two sections, which is noticed by the manometer and is used to calculate the rate of flow through the Venturimeter.

## 44) Vernier Caliper:

It is used to measure linear dimensions such as distance or straight line between two points. It is an ideal measuring tool to measure the diameter of spherical objects like pipes, cylinders as the jaws of the caliper can be positioned on both the sides of the circumference. It was invented by Pierre Vernier in 1631.

A Vernier caliper has the main scale that remains fixed and a moving Vernier scale. The main scale measures in millimetres or tenths of an inch. Using this measuring device precise small readings as low as 0.02 mm or 0.001 inches can be taken.

It can be used for three types of measurements that include outside distance such as length of an object, inside distance such as width or diameter of a groove or hole, and depth of a hole or height of a step.

The accuracy of the Vernier scale also depends on the ability of a person to detect the lines that are aligned and which are not aligned. The advanced calipers are digital as they come with an LCD to display readings. It reduces the chances of error in reading the scale.

## 45) Viscometer:

It is an instrument which is used to measure the viscosity of a fluid and semi-solid including the solid food products. Viscosity is the fluid's resistance to flow. By measuring the viscosity, the thickness or internal friction of a material can be measured or quantified. The units to measure viscosity are centipoise (cP) or Pascal-sec (Pa-s). For example, the viscosity of water is one centipoise (cP).

A wide range of viscometers is available for a wide range of applications. Such as classic capillary tube that lacks moving parts, and advanced hydraulic systems, Krebs-Stormer viscometer, and more.

Viscometers are very useful in quality assurance laboratories to check the flow behaviour of materials caused by wrong processing, formulation, and staling, etc. For example, it is widely used by food processing plants who are engaged in the production of fruit juices, ketchup, jam, gums, syrups, mayonnaise, honey, and more. It allows them to check food consistency in order to maintain the quality of the product.

Different viscometers work under different physical principles as per their design, components, and nature of the sample. Some of the types of this device are rotary viscometer, u-tube capillary viscometer, falling sphere viscometer, and rapid visco analyser (RVA), etc.

The working of some of the viscometers is described below:

• U-tube capillary viscometer: In this device, the liquid is made to flow through a U-shaped capillary channel. Then the time taken by the liquid to travel through a specific length of the channel is noted down as the efflux time, which is used to measure the viscosity.
• Bubble viscometer: In this device, the time takes by a bubble of gas to move through the fluid whose viscosity is to be tested is measured.
• Falling sphere viscometer: As the name suggests, in this device, a sphere of known size and density is made to fall through the given fluid. The time taken by the sphere to cover a certain distance in the fluid while falling through it is determined, which is used to measure the viscosity as per the Stokes' law.2

## 46) Wattmeter:

It is a professional, electric instrument that is used to measure the flow of current or electricity or electric power through high-voltage electricity lines. Along with the flow of current, it also measures the voltage and current values which can be used to calculate power in watts.

Wattmeters are mostly used in the transmission and distribution of electric power. The most common type of wattmeter is dynamometer type. It consists of an immovable coil that is connected in series to the electric circuit or lines and then to a movable coil that is connected to a resistor circuit which is parallel to the load.

The three main types of wattmeter are described below:

Electrodynamic: It consists of three coils out of which two are static current coils that are connected in series with the electrical circuit or lines and the last one is a movable potential coil connected in parallel with it and has a needle attached to it. When the current passes through the static coils that are in series, an electromagnetic field is generated that tends to move the coil that influences needle movement and value is displayed on the scale. In the absence of current or voltage, the needle stays at zero.

Electronic type: It has the electronic circuit that measures the current and voltage and multiply their values in another circuit and thus provides the result.

Digital type: It measures the current and voltage several thousand times in a second. These thousands of samples collected in a second are used to determine an average power usage in watts with the help of a computer chip. It can also tell the peak, average and low watts.

## 47) Wavemeter:

Wavemeter, which is also known as wavelength meter, is a scientific instrument that is used to measure the wavelength of laser beams with great precision. There are many types of wavemeter such as scanning wavemeters, and static instruments without any moving parts.

A wavemeter is an interferometer that measures only wavelengths. An interferometer measures wavelengths through interference using mirrors, e.g., a beam of light is split into two and then it is recombined again. The shape attained after it recombines is studied to take the measurement of the beam.

Generally, a wavemeter is typically of two types; scanning and static. The working of scanning type is similar to Scanning Michelson Interferometer. It comprises a light source, a detector, and three mirrors.

The light source is placed opposite to one of the mirrors, one mirror and the detector are positioned perpendicular to the light source and mirror that is opposite to it. The last mirror, which is half-silvered used to split the light beam; it is placed at some angle in the centre.

The laser from the light source hit the half-silvered mirror and gets divided into two parts, one part goes straight through and other part moves perpendicular to the first. Both parts hit the mirrors placed behind and above the centre mirror and rebound, and then they recombine by the half-silvered mirror. The recombined beam moves towards the detector that analyses its shape to provide the measurement.

On the other hand, static wavemeters are based on the Static Fizeau Interferometer. It lacks moving components but works on the same principle of reflection by mirrors.

## 48) Bolometer:

It is a device used to detect and measure heat or electromagnetic radiations of microwave energy. It was invented by Samuel Pierpont Langley, who was an American astronomer. In the beginning, it was used along with a telescope for quantifying infrared radiation. It uses an element whose resistance changes with temperature, e.g., thermistor, barretter, etc.

Barretter has a positive temperature coefficient, which means its resistance increases with an increase in temperature. On the other hand, the temperature coefficient of the thermistor is negative, which means its resistance decreases with the increases in temperature.

### Working of Bolometer:

The bloomer consists of a circuit in the form of a bridge. It has a thin metal layer which acts as an absorptive element that is connected to a thermal reservoir through a thermal link. When the radiation hits the thin metal layer, its temperature increases due to the absorption of radiations and becomes more than the reservoir temperature. A resistive thermometer that is connected to a thin layer is used to measure the temperature difference.

The main benefits of using a bolometer include:

• It is more efficient than conventional particle detectors in terms of sensitivity and energy resolution.
• It can be operated at room temperature so cooling is not required.
• It can also measure non-ionizing particles besides photons and ionizing particles.

## 49) Fluxmeter:

It is a scientific instrument that is used to measure the flux of a permanent magnet. In fact, this device is an advanced version of the ballistic galvanometer with certain benefits like heavy electromagnetic damping and low controlling torque.

It consists of a coil that hangs freely between the poles of a permanent magnet. The helices, which is made of silver strips, supplies the current into the coil. The current tends to reduce the controlling torque as much as it can. The coil's air friction damping remains negligible.

### How fluxmeter works:

The fluxmeter is connected to both ends of the search coil. Now, the flux linked with the coil is varied by separating it from the magnetic field or by reversing the magnetic field. These changes in flux produce electromotive force in the coil which results in the production of current in the search coil which passes through the flux meter. Due to the presence of current, the needle of the fluxmeter stars deflecting; the more is the change in flux, the more is the deflection.

As the changes in the magnitude of flux reduce, the coil stops moving due to electromagnetic damping caused by the low resistance circuit between the search coil and the fluxmeter.

There are many advantages of using a fluxmeter such as it is portable, its scale is calibrated in Weber meters, and the coil' deflection is not affected by the time taken by flux to change.