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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MCQ on EMI for NEET Students
A step-down transformer is connected to 240 volts line and 40 amperes of current is found to flow in the output load. The ratio of the turns in the primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in the primary coil will be
(A) 1600 ampere
(B) 2 ampere
(C) 4 ampere
(D) 1.5 ampere
Option b – 2 ampere
During amplification of output using a transformer, ……… remains unchanged.
(A) voltage
(B) frequency
(C) current
(D) magnetic field
Option b – frequency
If the value of the inductor is doubled and the capacitor is halved in an LC oscillator circuit, then the output signal
(A) remains the same.
(B) reduces to half.
(C) increases by half.
(D) doubles.
Option a – remains the same.
A step-up transformer operates on a 100 V line and supplies to a load of 1.5 A. The ratio of primary to secondary windings is 1 : 20. The primary current is
(A) 0.044 A
(B) 0.075 A
(C) 0.12 A
(D) 0.005 A
Option b – 0.075 A
An oscillator circuit consists of an inductance of 0.2 ml and a capacitor of 10 uF. The resonant frequency of the circuit is nearly
(A) 1.12 kHz
(B) 3.56 kHz
(C) 2.42 kHz
(D) 0.5 kHz
Option b – 3.56 kHz
In a transformer 210 volts a.c. voltage is increased to 2500 volts. If the number of turns in the secondary is 1000, then the number of turns in the primary will be
(A) 200
(B) 100
(C) 50
(D) 84
Option d – 84
An a.c. generator produced an output voltage E = 160sin(350t) volts, where t is in seconds. The frequency of a.c. voltage is
(A) 55.73 Hz
(B) 110 Hz
(C) 60.3 Hz
(D) 230 Hz
Option a – 55.73 Hz
A transformer with an efficiency of 90% works at 2 kW and 300 V. If the secondary voltage is 200 V, then the primary and secondary currents are respectively
(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
Loss of energy due to eddy currents in the dynamo can be decreased by
(A) doubling the core of the dynamo.
(B) tripling the core of the dynamo.
(C) laminating the core of the dynamo.
(D) coating the core of the dynamo with copper.
Option c – laminating the core of the dynamo.
A 50 Hz a.c. the current of crest value 4 A flows through the primary of a transformer. The mutual inductance between the primary and secondary is 0.25 H. The crest voltage induced in the secondary is
(A) 50 V
(B) 100 V
(C) 200 V
(D) 300 V
Option c – 200 V
The number of turns in the coil of an a.c. the generator is 4000 and the area of the coil is 0.15 m². The coil is rotated at the rate of cycles/s in a magnetic field of 0.2 Wb/m². 100 The peak value of the e.m.f generated is nearly
(A) 75.36 kV
(B) 100 kV
(C) 80.97 kV
(D) 157.1 kV
Option a – 75.36 kV
A transformer is employed to reduce 220 V to 20 V. The primary draws a current of 9 A and the secondary 80 A. The efficiency of the transformer is
(A) 20%
(B) 40%
(C) 70%
(D) 81%
Option d – 81%
The resonant frequency of a circuit is f. If the capacitance is made 9 times the initial value, then the resonant frequency will become
(A) f/3
(B) 3f
(C) f
(D) f/9
Option a – f/3
A transformer that has an efficiency of 90% is working on 200 V and 5 kW power supply. If the current in the secondary coil is 9 A, the voltage across the secondary coil and the current in the primary coil respectively are
(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
The armature coil of an a.c. the generator has 500 turns, each of area 4 m². It was rotating in a uniform magnetic field of B 0.5 T at an angular speed of 60 rad/s. It was found that in a certain position of the coil, the current in the circuit became zero. What was the flux in the coil?
(A) 200 Wb
(B) 1250 Wb
(C) 1300 Wb
(D) 1000 Wb
Option d – 1000 Wb
In a step-up transformer, the ratio of turns of primary to secondary is 1 : 8, and the primary voltage is 230 v. If the load current is 4 A, then the current in the primary is
(A) 20 A
(B) 10 A
(C) 32 A
(D) 1 A
Option c – 32 A
The core of the transformer is made up of
(A) soft iron.
(B) steel.
(C) iron.
(D) copper.
Option a – soft iron.
A step-down transformer converts a voltage of 2000 volts into 220 volts in the transmission line. If the number of turns in the primary coil is 1000, the efficiency of a transformer is 90% and its output power is 6 kW then calculate its input power and number of turns in the secondary coil.
(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: Parallel resonant circuit is called a rejector circuit. Reason: It rejects the current.
(A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(C) If the assertion is true but the reason is false.
(D) If the assertion is false but the reason is true
Option a – If both assertion and reason are true and the reason is the correct explanation of the assertion.
LC oscillations are produced when a charged condenser is allowed to discharge through the
(A) inductor.
(B) capacitor.
(C) resistor.
(D) diode.
Option a – inductor.
……… core choke coil is used to reduce alternating currents of radio frequency.
(A) Iron
(B) Air
(C) Air and iron
(D) Steel
Option b – Air
A suitable ac voltage can be obtained by using
(A) half-wave rectifier.
(B) full wave rectifier.
(C) transformer.
(D) none of the above.
Option c – transformer.
The primary winding of a transformer has 110 turns and its secondary winding has 220 turns. The primary is connected to an a.c. supply of 100 V and the current flowing in it is 5 A. The voltage and the current in the secondary are
(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
The peak value of induced e.m.f in a dynamo becomes two times when rotational velocity in its armature is
(A) tripled.
(B) half.
(C) made four times.
(D) doubled.
Option d – doubled.
A generator has an e.m.f. of 400 volts and internal resistance of 200 ohms. Its terminals are connected to a load of 5000 ohms. The voltage across the load is
(A) 220 volts
(B) 425 volts
(C) 385 volts
(D) 255 volts
Option c – 385 volts
The LC parallel resonant circuit ( EMI MCQ Class 12 )
(A) has a very high impedance.
(B) has a very high current.
(C) acts as the resistance of very low value.
(D) has zero impedance.
Option a – has a very high impedance.
A step-down transformer is used on a 900 V line to deliver 15 A at 120 V at the secondary coil. If the efficiency of the transformer is 80% the current drawn from the line is
(A) 3 A
(B) 30 A
(C) 0.3 A
(D) 2.5 A
Option d – 2.5 A
A coil of inductance 0.2 mH is connected to a capacitor of capacitance 200 pF. To what wavelength is this circuit tuned?
(A) 753.8 m
(B) 253.8 m
(C) 453.8 m
(D) 376.8 m
Option d – 376.8 m
……… induces an alternating voltage in the secondary coil of the transformer.
(A) Varying magnetic field
(B) Varying electric field
(C) Core of transformer
(D) Vibrations of primary cell
Option a – Varying magnetic field
We covered all the EMI MCQ class 12 above in this post for free so that you can practice well for the exam.
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