## Electrical MCQs1) Which of the given motor has insufficient starting torque at full load speed with the same H.P. ratings? - Three-phase Induction motor
- Shunt motor
- Synchronous motor
- Differential compound motor
2) Which of the given networks are based on the compensation theorem? - Unilateral network
- Bilateral network
- Linear and non-linear network
- Distributed network
3) The ratio of the Mechanical Impedance is - RMS force to RMS displacement
- RMS velocity to RMS acceleration
- RMS force to RMS velocity
- RMS current to RMS speed
Force/Velocity = Mechanical impedance. Impedance is similar to resistance in D.C. In A.C. and an additional opposing force acts in addition to resistance. The total opposing force is known as Impedance. 4) In a two-wattmeter method, the measured power was 40kW At 0.8 lagging power factor. Calculate the reading of each wattmeter - W
_{1}= 34.875 and W_{2}= 5.125 - W
_{1}= 33.875 and W_{2}= 6.125 - W
_{1}= 38.875 and W_{2}= 6.125 - W
_{1}= 32.875 and W_{2}= 5.125
Given; Power(P) = 40 Kw and cos?φ = 0.7 lagging Let's suppose W1 and W2 are the readings of two wattmeters method Then, P = W1 + W2 = 40 kW Now, cos?φ = 0.8 lagging, = tan?(cos We know the formula of two wattmeter method to calculate the power measurement Therefore, W And we know that W Adding the above equation we get, W 2 W W And, we know that W Putting the value of W 33.875+ W W 5) Under no-load conditions, the transmission line carrying a current because of - Heating effect
- Capacitance effect
- Chemical effect
- Transmission effect
6) In a synchronous machine, the V curve is drawn between which of the given axis. - Field current on X-axis and no-load current on Y-axis
- Armature current on X-axis and the no-load current in Y-axis
- Field current on X-axis and armature current on Y-axis
- Armature current on X-axis and filed current on Y-axis
The graph located above represents the V curve of a synchronous motor. The middle line represents the unity power factor line and the right-hand side of the unity power factor line considered as lagging power factor line. It reduces the external D.C. voltage source using the controlled rectifier, which causes more lagging current to make constant air gaps, and during this process, the field current is kept lower. 7) The spot welding is used for - Joint thick sheets
- Rough surface
- Thin metal sheets(10-12mm)
- T shape welding
8) In a 3-Ø induction motor, the starting current is 8 times the rated current, and the rated slip is 6 %, then find the ratio of starting torque to full load torque. - 1
- 1.5
- 1.75
- 2
Given; I = S = r = (I = (5) = 25×0.06=1.5 9) The single-phase reluctance machine works as a generator when the value of ? is - Infinitive
- Zero
- Unity
- Positive
When the value of is negative, the developed toque will be reversed, so the machine will act as a generator. 10) In a series circuit, the value of resistance is 40 ohm, and Inductance is 40mH . If the 100V of an A.C. source is connected to the circuit with 80Hz Frequency, find the value of current flowing through the resistance. - 1.23 A
- 2.23 A
- 3.33 A
- 4.33 A
First, we need to calculate the impedence We know that Impedence = √(R2+XL Here, XL= 2πfL Given ; F = 80Hz L = 40mh= 40×10-3 XL= 2π×(80)× 40×10-3= 20.096 So the value of XL =√((40) 44.76 ohm 11) The Primary reason for D.C. motor Preferred over A.C. motor - Constant speed operation
- High-speed operation
- Variable speed operation
- Low-speed operation
12) If the five bulbs having power ratings 5W,10W,25W,35W, and 50W, which one will have the highest resistance? - 5W bulb
- 50W bulb
- 25W bulb
- 10W bulb
We know the formula power P = VI = V Here, we can see that R It means resistance is inversely proportional to power, so the bulb having the least power rating will offer the highest resistance. 13) If the number of turns 4 times and length becomes double in a solenoid, and keeping the cross-sectional area are same, then find the ratio of Inductance (Older to newer). - 2
- 4
- 6
- 8
We know the formula of Inductance L = µ0 N L= N Given; N l = 2l L2 α N2 L 14) Find the term ratio of the bridge rectifier at 20V D.C. output when the supply voltage is 230V, 50Hz. - 10:1
- 20:1
- 1:15
- 1:13
15) In the given 8085 microprocessor, the restart instruction(RST) is 8 instruction. What would be the transfer program execution to a given location? - (0020)
_{H} - (0030)
_{H} - (0040)
_{H} - (0010)
_{H}
Given; Restarts instructions (RST)= 8 So the location = 8×8 =(64) = (0040) 16) The purpose of dummy coil in D.C. machine is - to reduce losses
- to Improve machine efficiency
- to maintain a mechanical balance of armature
- to reduce the cost of the machine
17) The load factor of a plant is 0.8, and the capacity factor is 0.7. If the maximum demand on the plant is 600 MW, find the reserve capacity of the plan - 25
- 85
- 105
- 120
Given; Maximum demand = 600MW Load factor = 0. Capacity factor = 0.7 To calculate the reserve capacity of the plant first, we need to calculate the Plant load factor. Reserve capacity of plant = Plant capacity - Maximum demand = 685 - 600 = 85 MW 18) A bulb of power rating 9kW draws a current 30 A. Find the applied Volage - 220 V
- 240 V
- 280 V
- 300 V
Given; Power(P) = 9kW = 9000W Current (I)= 30 A We know that Power = Product of Voltage and current P = V × I 19) In the MKS system, the value of 3 kW is equal to - 2.013Hp
- 3.013Hp
- 4.021Hp
- 5.021Hp
1Hp equals 746 electrical watts, which is 0.746 kW. If you reverse the math and make 1kW a reference, we will get 1hp = 0.746kW X = 3 W X = (3kW×1Hp)/0.746 So 3kW equals 4.021Hp 20) The resistivity of a conductor depends on - Length
- Current
- Voltage
- Power
The resistivity of a material refers to the resistance of a wire of that material of unit length and unit cross-sectional area. Resistance = ρ= A × resistance/A Here, ρ=resistivity; l = length and A = cross-sectional area. The S.I. unit for resistivity is the ohm-meter. The resistivity of a material depends on its type and the temperature of the conductor, but not on its dimension. A good conducting material has less resistivity, whereas a bad conducting material or insulator has high resistivity. The resistivity of semiconductor material usually lies between conductor and insulator. 21) A 200 kVA transformer has a full load copper loss of 400 W and iron loss 200 W. The maximum efficiency of the transformer will occur when a total loss is - 500 W
- 600 W
- 1500 W
- 1600 W
Given; full load copper loss = 400 W iron loss = 200 W The maximum efficiency of a transformer occurs when the copper loss becomes equal to the core loss. Here, Total loss = full load copper loss (400 W) + iron loss (200 W) = 600 W Therefore, maximum efficiency of the transformer total loss = 600 W 22) A 4 pole, three-phase induction motor is supplied by 50Hz frequency by a three-phase source. If the rotor of the motor rotates at 600 rpm, find the sli - 0.2
- 0.4
- 0.6
- 0.8
Given; No of poles (P) = 8 Frequency (f) = 50Hz Rotor speed (Nr) = 600 rpm In the three-phase induction motor, the speed of the synchronous motor is given by 23) TRIAC is operated at - Low Frequencies
- Power Frequencies
- High frequencies
- All of these
24) Five thyristors each of 2000 V rating are connected in series with a power circuit of 5 V.K. Find the percentage series derating factor? - 40
- 50
- 60
- 70
Given; Total voltage = 5 KV = 5 ×10 Number of thyristors(n) = 5 Rating of each thyristor = 2000 V So, the percentage efficiency is given by 25) In an intrinsic semiconductor, the number of holes is ....... the number of electrons. - Equal to
- More than
- Less than
- None of these
26) Find the value of emitter current of a transistor that has ADC = 0.5 and base current = 120 �A - 0.01 mA
- 1.24 mA
- 0.04 mA
- 0.24mA
Given; Base current I ADC (α) = 0.5 I We know that, I Where, I I I Therefore, I And, I = (1+1) × 120 µA = 2 × 120 µA = 240 µA = 240×10 27) Which of the given material is used for making light-emitting diodes? - Si
- Ge
- GaAs
- Fe
GaAs (Gallium Arsenide) is used for making light-emitting diodes (LEDs). In GaAs, the number of photons(Packet of energy) is enough to create a visual light source. In semiconductors, Si comes first, but unfortunately, it is not used to make LEDs. GaAs is a direct bandgap semiconductor with minimum conduction bandgap. The maximum valence band lies on a perpendicular straight line so the recombination can occur; thus, the conserving momentum can emit visible light. 28) Noise is a function of which of the given term - Momentum
- Acceleration
- Voltage
- Bandwidth
29) The displacement measuring Instrument LVDT works on the principle of - Fleming Left-hand rule
- Mutual Induction
- Linear induction
- Linear capacitance
30) Which of the gien material does not change the resistance with varying temperature - Gallium
- Manganin
- Tungsten
- Copper
31) In a power plant, the maximum demand is 100MW, and the sum of individual maximum demand is 70 M.W. Calculate the diversity factor - 0.5
- 0.6
- 0.7
- 0.8
Given; Individual maximum demand = 70 MW Power plant maximum demand = 100 MW 32) Which of the following is a series type unbalanced fault that occurs in a power system - Single line to double line fault
- Double line to double line fault
- The line to line fault
- Open conductor fault
: In a three-phase power system, electrical faults are divided into two categories, open circuit, and short circuit faults Open circuit faults: Open circuit faults occurs mainly due to conductor failure. The primary cause of these faults incorporates failures of overhead lines and melting of a fuse in one or more phases. It is also called series faults 33) The three-phase oil circuit breaker rated as 2000 MVA, 66 K.V., 6 SEC. Find the making current - 13.44 kA
- 19.43 kA
- 22.76 kA
- 27.55 kA
Given; Symmetrical breaking capacity = 2000 MVA VL = 66 Kv Therefore, So, the making current = 2.55 × symmetrical breaking current = 2.55 × I = 2.55 × 7.62 kA = 19.43 kA 34) In a three-phase induction motor, the rotor power output is 20 kW, and the value of the corresponding slip is 8 %. Find the rotor copper loss of the motor - 1288 W
- 1596 W
- 2033 W
- 2522 W
Given: Rotor power output (P Slip (S) = 8 % = 0.08 So, Rotor power output (P Therefore, Rotor copper loss = sP 35) Which of the given relays can resist the possible major fault in the transformer - Current relay
- Frequency relay
- Buchholz relay
- Overcurrent relay
36) In a three-phase transformer, the primary winding is delta connected, and the secondary winding is star connected, and the secondary to primary turn ratio per phase is 15. If 240 V is applied to the transformer's primary side, find the secondary voltage of the transformer. - 5532 V
- 6625 V
- 6235 V
- 7325 V
Given; ∆/γ connection Secondary to primary turn ratio = 15 V1 = 240 V So, 37) Which of the given diode is called hot-carrier dioxide? - P.N. junction diode
- Schottky diode
- Light-emitting diode
- Zener diode
Schottky diode is called a hot-carrier diode. It is formed when metal and semiconductor are interfaced. It has a low forward voltage drop and fast switching response, so they are used in high-power applications such as high-power rectifiers. They are preferred for high frequency like a radiofrequency application over the normal p-n junction diode. 38) In a transformer, the humming sound is primarily due to - Overflow of oil
- Magnetostriction
- Flux leakage
- Lamination of transformer
39) When a 20 A current flows for 6 minutes, calculate the amount of electricity transferred. - 7200 C
- 6400 C
- 8400 C
- 5400 C
Given; I = 20 A t= 6 minutes we know that 40) Find the barrier potential for Si junction diode at 100 C, calculate its value at 400 C is 0.9 V - 0.75 V
- 0.96 V
- 1.20 V
- 0.60
Given; T T We know that, ∆V= -0.002(T = -0.002(10- 40) = 0.06 V So the barrier potential at 10 V 41) An induction machine is operated with frequencies that are given in the ratio 3:7 without changing the voltage. Find the starting torque of the machine for the given frequencies - 2:7
- 3:7
- 4:7
- 5:7
42) The voltage range is non uniform. Its type is - Electrostatic instrument
- Potentiometer
- Galvanometer
- Multimeter
In an electrostatic instrument, the voltage range is uniform. We know that For MI, Q is directly proposal to the square of the current. 43) Which of the given test is used for the calculation of the inertia of the rotor? - Sinners test(Back to Backtest)
- Low voltage test
- High Voltage test
- Retardation test
44) In a series resonance circuit, what is the value of the Impedance at half power frequencies
45) A galvanometer having the value of coil resistance is 120 Ω gives a full-scale deflection when a current of 3mA is passed through it. Find the value of the resistance, which can convert a galvanometer into an ammeter, giving a full-scale deflection for a current of 12 A. - 0.07 Ω
- 0.09 Ω
- 0.11 Ω
- 0.03 Ω
Given; Rg = 120 Ω Ig = 3 mA I = 12 A Rs ? If the galvanometer's resistance is considered as Rg, it gives a full-scale deflection when the current Ig is passed through it. So, V = RgIg V = 3mA × 120Ω Now, consider a shunt resistor Rs, which is connected in parallel to a galvanometer. When we consider a total current passing through the circuit is I Then, I = Is + Ig and V = IsRs = (I-Ig)Rs because (Is = I-Ig) from the above equation (I-Ig)Rs = IgRg (12 - 3 × 10 (11.997)Rs = 0.36 46) Find the numbers of address lines needed to address a memory size 64K - 10
- 12
- 14
- 16
Memory size = 64K, it means = 64 × 1024 bytes = 2 Therefore, The number of address lines needed to address a memory size 64K = 16 47) A 3 phase Induction motor having 70 Hz frequency draws a power of 80 kW from mains. If the stator losses are 4kW and rotor emf oscillates at 120 oscillations per minute, find the rotor copper losses - 0.26 kW
- 0.54 kW
- 0.10 kW
- 0.99 kW
Given; fs = 70Hz fr = 120/60 = ½ Stator loss = 4kW Rotor Copper loss ? We know that, Rotor input = Stator input - stator loss = 80 - 4 = 76kW Rotor copper loss = S × Rotor input 48) In an induction motor, crawling is caused by - High Voltage
- Heavy loads
- Harmonic produced in the motor
- Improper design of machine
49) In a ferromagnetic material, the neighboring atomic magnetic moments are - Predominantly unequal in small regions of material.
- Predominantly constant in small regions of material.
- Predominantly unequal and parallel throughout the material.
- Predominantly equal and parallel throughout the material.
50) N-type and P-type extrinsic semiconductors are formed by adding the impurities of which valency. - Tertavalent and pentavalent
- Trivalent and pentavalent
- Pentavalent and trivalent
- Trivalent and tetravalent.
51) An 8 pole, 1600 rpm D.C. lap wound generator has 1680 conductors. If the flux per pole is 0.04 weber, find the emf of the generator. - 1600 V
- 1792 V
- 1982 V
- 2020 V
Given; P = 8 N = 1600 rpm Z = 1680 Ø = 0.04 Weber In lap wound generator A=P=8 E ? We know that the emf generated. 52) The input voltage of a boost regulator is 8V, and the average output voltage is 24V. Find the duty cycle.
Given; Vo = 24 V Vs = 8 α =? We know that, 53) In which of the given single-phase motor, the rotor has no teeth or winding? - Shaded pole motor
- Capacitor start motor
- A permanent capacitor run the motor
- Hysteresis motor
54) 1 volt can be expressed as - 1 joule/weber
- 1 joule/ columb
- 1 joule/ohm
- 1 watt/ Joule
Unit of voltage = Joule/ coulomb 55) A single-phase having a rating of 11 kVA, 4400/440 V, 50 Hz, distribution transformer is to be connected as an auto-transformer to get an output voltage of 3260 V. Find its maximum kVA rating as an autotransformer. - 111
- 121
- 144
- 169
We know that voltage rating is additive that is 4400+440 = 4880 V Let a (KVA) 56) The starting current of a three phase induction motor is 3 times the rated current, while the rated slip is 8 %. Find the ratio of starting toque to full load toque - 0.5
- 0.75
- 0.72
- 0.80
Given; I S We know that, 57) The Y - 8100
- 7200
- 5900
- 4700
Given; Number of buses, N = 200 Sparsity, s = 0.7 We know that, the equation to calculate transmission line N = (200) = 5900 58) A negative sequence really is usually used to protect - A transformer
- An Alternator
- A transistor
- A Junction
59) A potentiometer is usually a - Digital Instrument
- Deflection type instrument
- Null type instrument
- None of these
60) An amplifier has a gain of 30 without feedback. If 20 % of the output voltage is a feedback using its resistance negative feedback circuit, find the overall gain? - 3.67
- 4.28
- 9.85
- 7.47
Given; A = 30 And β = 20 % = 0.2 Because feedback is negative Next TopicClass 12 Physics MCQ |