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EMI mcq Class 12. We covered all the EMI mcq Class 12 in this post for free so that you can practice well for the exam.
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A step-down transformer connected to a 240 V source delivers 40 A to the load. If the primary to secondary turn ratio is 20:1 and the efficiency is 100%, what is the current in the primary winding?
(A) 1600 A
(B) 2 A
(C) 4 A
(D) 1.5 A
Option b – 2 A
When a transformer is used to amplify the output, which of the following stays constant?
(A) Voltage
(B) Frequency
(C) Current
(D) Magnetic field
Option b – Frequency
In an LC oscillator, if the inductance is doubled and capacitance is halved, what effect does it have on the output signal?
(A) Remains unchanged
(B) Becomes half
(C) Increases by half
(D) Becomes double
Option a – Remains unchanged
A step-up transformer is connected to a 100 V power source and delivers a current of 1.5 A to a load. The turn ratio between the primary and secondary coils is 1:20. What is the current in the primary?
(A) 0.044 A
(B) 0.075 A
(C) 0.12 A
(D) 0.005 A
Option b – 0.075 A
An oscillator has an inductance of 0.2 mH and a capacitance of 10 µF. What is its approximate resonant frequency?
(A) 1.12 kHz
(B) 3.56 kHz
(C) 2.42 kHz
(D) 0.5 kHz
Option b – 3.56 kHz
A transformer increases voltage from 210 V AC to 2500 V. If the secondary has 1000 turns, how many turns are in the primary?
(A) 200
(B) 100
(C) 50
(D) 84
Option d – 84
An AC generator produces a voltage given by E = 160 sin(350t). What is the frequency of this voltage?
(A) 55.73 Hz
(B) 110 Hz
(C) 60.3 Hz
(D) 230 Hz
Option a – 55.73 Hz
A transformer working at 90% efficiency operates with 2 kW input and 300 V. If the output voltage is 200 V, what are the primary and secondary currents?
(A) 9 A, 6.66 A
(B) 6.66 A, 2 A
(C) 6.66 A, 9 A
(D) 2 A, 9 A
Option c – 6.66 A, 9 A
Which method helps reduce eddy current losses in a dynamo?
(A) Doubling the dynamo core
(B) Tripling the dynamo core
(C) Laminating the core
(D) Coating the core with copper
Option c – Laminating the core
An Alternating Current of peak value 4 A at 50 Hz flows through a transformer’s primary. If mutual inductance is 0.25 H, what is the induced peak voltage in the secondary?
(A) 50 V
(B) 100 V
(C) 200 V
(D) 300 V
Option c – 200 V
A generator has 4000 turns, a coil area of 0.15 m², rotates at 100 cycles/s in a magnetic field of 0.2 Wb/m². What is the approximate peak emf produced?
(A) 75.36 kV
(B) 100 kV
(C) 80.97 kV
(D) 157.1 kV
Option a – 75.36 kV
A transformer lowers the voltage from 220 V to 20 V. If the primary current is 9 A and the secondary current is 80 A, what is its efficiency?
(A) 20%
(B) 40%
(C) 70%
(D) 81%
Option d – 81%
If a circuit’s resonant frequency is f, and its capacitance is increased nine times, what will be the new frequency?
(A) f/3
(B) 3f
(C) f
(D) f/9
Option a – f/3
A transformer with 90% efficiency is powered by a 200 V, 5 kW supply. If 9 A flows through the secondary, what are the secondary voltage and primary current?
(A) 500 V, 25 A
(B) 450 V, 15 A
(C) 450 V, 15 A
(D) 600 V, 25 A
Option a – 500 V, 25 A
An AC generator has an armature coil with 500 turns, each of area 4 m², rotating in a magnetic field of 0.5 T at 60 rad/s. When the coil reaches a position with zero current, what is the magnetic flux through the coil?
(A) 200 Wb
(B) 1250 Wb
(C) 1300 Wb
(D) 1000 Wb
Option d – 1000 Wb
A step-up transformer has a 1:8 turn ratio. If the input voltage is 230 V and the output current is 4 A, what is the primary current?
(A) 20 A
(B) 10 A
(C) 32 A
(D) 1 A
Option c – 32 A
The core material used in transformers is typically
(A) Soft iron
(B) Steel
(C) Iron
(D) Copper
Option a – Soft iron
A step-down transformer reduces 2000 V to 220 V with 90% efficiency and outputs 6 kW of power. If the primary has 1000 turns, what are the input power and secondary turns?
(A) 6.67 kW, 110
(B) 3.67 kW, 130
(C) 6.677 kW, 90
(D) 3.67 kW, 150
Option a – 6.67 kW, 110
Assertion: A parallel resonant circuit is known as a rejector circuit.
Reason: It blocks current flow.
(A) Both assertion and reason are true; reason explains the assertion
(B) Both are true; reason does not explain the assertion
(C) Assertion is true; reason is false
(D) Assertion is false; reason is true
Option a – Both assertion and reason are true; reason explains the assertion
LC oscillations are triggered when a charged Capacitor is discharged through a
(A) Inductor
(B) Capacitor
(C) Resistor
(D) Diode
Option a – Inductor
Which type of core is used in a choke coil to reduce high-frequency alternating currents?
(A) Iron
(B) Air
(C) Air and iron
(D) Steel
Option b – Air
What component is best suited to obtain an appropriate AC voltage?
(A) Half-wave rectifier
(B) Full-wave rectifier
(C) Transformer
(D) None of the above
Option c – Transformer
A transformer has 110 primary turns and 220 secondary turns. If it is connected to 100 V AC and draws 5 A, what are the secondary voltage and current?
(A) 200 V, 2.5 A
(B) 240 V, 10 A
(C) 60 V, 20 A
(D) 120 V, 20 A
Option a – 200 V, 2.5 A
What happens to the peak emf of a dynamo when its rotational speed is doubled?
(A) Becomes three times
(B) Becomes half
(C) Increases four times
(D) Doubles
Option d – Doubles
A generator with 400 V emf and internal resistance of 200 ohms is connected to a 5000-ohm load. What is the voltage across the load?
(A) 220 V
(B) 425 V
(C) 385 V
(D) 255 V
Option c – 385 V
The LC parallel resonance circuit is characterized by
(A) Very high impedance
(B) Very high current
(C) Very low resistance
(D) Zero impedance
Option a – Very high impedance
A step-down transformer is used with a 900 V supply to deliver 15 A at 120 V. If its efficiency is 80%, what is the current drawn from the supply?
(A) 3 A
(B) 30 A
(C) 0.3 A
(D) 2.5 A
Option d – 2.5 A
A coil with an inductance of 0.2 mH is paired with a 200 pF Capacitor. What is the wavelength the circuit is tuned to?
(A) 753.8 m
(B) 253.8 m
(C) 453.8 m
(D) 376.8 m
Option d – 376.8 m
What is responsible for generating an alternating voltage in a transformer’s secondary winding?
(A) Changing magnetic field
(B) Varying Electric Field
(C) Transformer core
(D) Vibrating primary cell
Option a – Changing magnetic field
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