R4RIN – MCQs, Mock Tests | IIT JEE IIT JEE Electromagnetic Induction Electromagnetic Waves Part-1

The electromagnetic waves of much short wavelength (25 mm to 5 mm) were produced and observed by:

1. Maxwell
2. Hertz
3. Marconi
4. J.C. Bose

✅ Correct Answer: 4

A transformer has an efficiency of 80% and works at 100 V and 4 kW. If the secondary voltage is 240 V then the value of primary current is:

1. 28.5 A
2. 40 A
3. 20 A
4. 80 A

✅ Correct Answer: 2

Electromagnetic waves are transverse in nature is evident by:

1. polarization
2. interference
3. reflection
4. diffraction

✅ Correct Answer: 1

A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis then:

1. a current will be induced in the coil
2. no current will be induced in the coil
3. an emf and a current both will be induced in the coil
4. none of these

✅ Correct Answer: 2

An inductance has a high resistance to AC and low to DC. When a DC voltage source having same AC component superimposed on it sends current through an inductance to a load resistance:

1. the DC voltage falls appreciably across the AC component falls only a small amount
2. the AC and DC voltages fall by the same small percentage
3. the AC voltage falls appreciably across the load and DC voltage falls by only a small amount
4. both AC and DC voltage fall to nearly zero

✅ Correct Answer: 1

The conduction current is same as displacement current when source is:

1. AC only
2. DC only
3. both AC or DC
4. neither DC nor AC

✅ Correct Answer: 3

The reactance of an inductor connected with DC voltage is:

1. zero
2. infinity
3. 1?
4. none of these

✅ Correct Answer: 2

In L-R circuit the time constant is given by:

1. LR
2. R/L
3. L/R
4. 1/LR

✅ Correct Answer: 3

According to Faradays law the total charge induced in a conductor that is moved in a magnetic field depends upon:

1. initial magnetic flux
2. final magnetic flux
3. rate of change of magnetic flux
4. change in magnetic flux

✅ Correct Answer: 4

If a current of 3 A flowing in the primary coil is reduced to zero in 001 s then the induced emf in the secondary coil is 1500 V the mutual inductance between the two coils is:

1. 0.5 H
2. 5 H
3. 1.5 H
4. 10 H

✅ Correct Answer: 2

The resonant frequency of a series circuit consisting of an inductance 200 ?H a capacitance of 00005 ?F and a resistance of 10? is:

1. 480 kHz
2. 503 kHz
3. 460 kHz
4. 607 kHz

✅ Correct Answer: 2

he average value for half cycle in a 200 V AC source is:

1. 180v
2. 200v
3. 220v
4. none of these

✅ Correct Answer: 1

An electric charge oscillating with a frequency of 1 kilo cycles/s can radiate electromagnetic waves of wavelength:

1. 100 km
2. 200 km
3. 300
4. 400 km

✅ Correct Answer: 3

The frequency of voltage for an AC circuit if the equation of alternating voltage is V = 200 sin 314t is:

1. 50 Hz
2. 60 Hz
3. 55 Hz
4. 65 Hz

✅ Correct Answer: 1

In a step-up transformer the number of turns in:

1. primary are less
2. primary are more
3. primary and secondary are equal
4. primary are infinite

✅ Correct Answer: 1

A fully charged capacitor is allowed to discharge through an inductor of 05 mH The initial current through the inductance rises from 0 to 15 A in 25?s The instantaneous voltage across it is:

1. 75V
2. 125V
3. 300V
4. 1875V

✅ Correct Answer: 3

In an electromagnetic wave the average energy density is associated to:

1. electric field only
2. magnetic field only
3. equally with electric and magnetic fields
4. average energy density is zero

✅ Correct Answer: 3

The nature of electric field in the region between the two plates of a capacitor while charging is:

1. always constant
2. varying
3. depends on value of C and R
4. depends on emf of battery

✅ Correct Answer: 2

Which one of the following can produce maximum induced emf?

1. 50 A DC
2. 50 A 50 Hz AC
3. 50 A 500 Hz AC
4. 100 A DC

✅ Correct Answer: 3

An output voltage of E = 170 sin 377t is produced by an AC generator where t is in sec then the frequency of alternating voltage will be:

1. 50 Hz
2. 110 Hz
3. 60 Hz
4. 230 Hz

✅ Correct Answer: 3

If 20 V battery is connected to primary coil of a transformer then output voltage is:

1. zero
2. 20 V
3. 10 V
4. none of these

✅ Correct Answer: 1

If a dry cell of emf 1.5 V is connected across the primary of a step-up transformer of turn ratio 3: 4 then the voltage developed across the secondary is:

1. 30 V
2. 5 V
3. zero
4. 2.5 V

✅ Correct Answer: 3

In a series L-C-R circuit the voltage across each resistance inductance and capacitance is 10 V If the resistance is short-circuited the current in the circuit will be:

1. zero
2. infinite
3. 10A
4. 5A

✅ Correct Answer: 2

The magnetic field between the plates of radius 12 cm separated by distance of 4 mm of a parallel plate capacitor of capacitance 100 pF along the axis of plates having conduction current of 015 A is:

1. zero
2. 1.5 T
3. 15 T
4. 0.15 T

✅ Correct Answer: 1

An AC circuit consists of a resistance and a choke in series. The resistance is of 220? and choke is of 0.7 H. The power absorbed from 220 V and 50 Hz source connected with the circuit is:

1. 120.08 W
2. 109.97 W
3. 100.08 W
4. 98.08 W

✅ Correct Answer: 2

A point source of electromagnetic radiation has an average power output of 800 W. The maximum value of electric field at a distance 4.0 m from the source is:

1. 64.7 V/m
2. 57.8 V/m
3. 56.72 V/m
4. 54.77 V/m

✅ Correct Answer: 4

Two pure inductor coils of self-inductance L each are connected in series the net inductance is:

1. L
2. 2L
3. L/2
4. L/4

✅ Correct Answer: 2

The correct sequence of the increasing wavelength of the given radiation sources is:

1. radioactive sources X-ray tube crystal oscillator sodium vapour lamp
2. adioactive crystal oscillator
3. X-ray tube radioactive source radioactive source sodium vapour lamp
4. X-ray tube crystal oscillator radioactive source sodium vapour lamp

✅ Correct Answer: 2

When the current through a solenoid increases at a constant rate the induced current:

1. is a constant and in the direction of inducing current
2. is a constant and is opposite to the direction of inducing current
3. increases with time and is in the direction of inducing current
4. increases with time and is opposite to the direction of inducing current

✅ Correct Answer: 2

A motor

1. converts electrical energy into mechanical energy
2. converts mechanical energy into electrical energy
3. converts electrical energy into magnetic energy
4. produces mechanical energy

✅ Correct Answer: 3

Induction coil is based on the principle of

1. rheostate
2. self induction
3. mutual induction
4. induction

✅ Correct Answer: 3

The core of any transformer is laminated so as to:

1. reduce the energy loss due to eddy currents
2. make it light weight
3. make it robust and strong
4. increase the secondary voltage

✅ Correct Answer: 1

In an L-C-R circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged the inductance should be changed from L to:

1. 4L
2. 2L
3. L/2
4. L/4

✅ Correct Answer: 3

A choke coil is preferred to a rheostat in AC circuit then:

1. it consumes almost zero power
2. it increases current
3. it increases power
4. it increases voltage

✅ Correct Answer: 1

In the case of dc motor if the current flowing through the armature coil minimum induced emf is

1. zero
2. maximum
3. one half of maximum
4. one fourth of maximum

✅ Correct Answer: 2

A 50 mH coil carries a current of 2 A the energy stored in joule is:

1. 1
2. 0.05
3. 0.1
4. 0.5

✅ Correct Answer: 1

The induced e. m. f. in a coil rotating in a uniform magnetic field depends upon

1. only on total number of turns in the coil.
2. Only on magnetic field
3. Area of coil and speed of rotation
4. All of the above

✅ Correct Answer: 4

What is the mutual inductance of coil and solenoid if a solenoid of length 0.50 m and with 5000 turns of wire has a radius 4 cm and a coil of 700 turns is wound on the middle part of the solenoid?

1. 44.17 mH
2. 48.98 mH
3. 34.34 mH
4. 36.73 mH

✅ Correct Answer: 1

In step-up transformer the turn ratio is 1:2. A leclanche cell (emf = 1.5V) is connected across the primary the voltage developed in the secondary would be:

1. 3.0 V
2. 0.75 V
3. 1.5 V
4. zero

✅ Correct Answer: 4

Iron core chokes are used for reducing low frequency ac because

1. iron core is good.
2. Iron core has low permeability
3. With iron core self inductance increases
4. none of these

✅ Correct Answer: 3

A closed circuit consists of a source of emf E and an inductor coil of inductance L connected in series The active resistance of whole circuit is R At the moment t = 0 inductance of coil abruptly decreased to L/n Then current in the circuit immediately after is:

1. zero
2. E/R
3. nE/R
4. E/nR

✅ Correct Answer: 3

When the current changes from +2 A to -2A in 005 s an emf of 8V is induced in a coil The coefficient of self-induction of the coil is:

1. 0.1 H
2. 0.2 H
3. 0.4 H
4. 0.8 H

✅ Correct Answer: 1

A coil is rotated in a uniform magnetic field about an axis perpendicular to the field. The emf induced in the coil would be maximum when the plane of coil is:

1. parallel to field
2. perpendicular to field
3. at 450C to field
4. none of these

✅ Correct Answer: 2

The voltage of domestic AC is 200 V. What does this represent?

1. Mean voltage
2. Peak voltage
3. Root mean voltage
4. Root mean square voltage

✅ Correct Answer: 4

A coil of wire of radius R has 200 turns and a self-inductance of 108 mH. The self-inductance of a similar coil of 500 turns will be:

1. 375 mH
2. 527 mH
3. 675 mH
4. none of these

✅ Correct Answer: 3

When the speed of the coil of generator is increased

1. the induced emf decreases but frequency increases.
2. the induced emf increases but frequency decreases
3. the induced emf increases and frequency also increases
4. both emf and frequency remain same

✅ Correct Answer: 3

One 10 V 60 W bulb is to be connected to 100 V line. The required self-inductance of induction coil will be: (f = 50 Hz)

1. 0.052 H
2. 2.42 H
3. 16.2 H
4. 16.2 mH

✅ Correct Answer: 1

The time constant of C-R circuit is:

1. 1/CR
2. C/R
3. CR
4. R/C

✅ Correct Answer: 3

A 50 Hz AC current of crest value 1 A flows through the primary of a transformer. If the mutual inductance between the primary and secondary be 0.5 H the crest voltage induced in the secondary is:

1. 75V
2. 150V
3. 100V
4. none of these

✅ Correct Answer: 3

If a current increases from 0 to 1 A in 0.1 s in coil of 5 mH then the magnitude of the induced emf will be:

1. 0.005 V
2. 0.5 V
3. 0.05 V
4. 5 V

✅ Correct Answer: 3

A coil of inductance L = 300 mH and resistance R = 140 m? is connected to a constant voltage source. Current in the coil will reach to 50% of its steady value after time t equal to:

1. 155s
2. 0.755s
3. 0.155s
4. 1.48s

✅ Correct Answer: 4

In the case of charging or discharging of a capacitor RC has units of

1. Ohm
2. A-F
3. Ohm-m
4. sec

✅ Correct Answer: 4

A coil is wound on a frame of rectangular cross-section If the linear dimensions of the frame are double and the number of turns per unit length of the coil remains the same then the self inductance increases by a factor of

1. 6
2. 12
3. 8
4. 16

✅ Correct Answer: 3

Current in a 10 milli henry coil increases uniformly from zero to one ampere in 0.01 second then the value of induced e. m. f. is

1. + 1 V
2. 2 V
3. - 1 V
4. - 2 V

✅ Correct Answer: 3

A resistor and an inductor are connected to an ac circuit whose supply is 200 V. An ac voltmeter across R reads 150 V. This voltmeter across inductor will read nearly

1. 50 V
2. 132 V
3. 148V
4. 196V

✅ Correct Answer: 2

In LR circuit the time constant is given by

1. LR
2. R / L
3. L / R
4. 1 / LR

✅ Correct Answer: 3

The current drawn from the primary of a transformer which steps down 220 V to 22 V at 0.1 amp. Shall be

1. 1 amp
2. 0.1 amp
3. 0.2 amp
4. 0.01 amp

✅ Correct Answer: 4

A copper plate flat pendulum and a copper plate pendulum with slots in it but of same dimension are made to oscillate in a magnetic field. Then

1. both will show damping at the same rate
2. flat pendulum shall show more damping
3. plate with slots shall show more damping
4. there will be no damping

✅ Correct Answer: 2

When a coil moves towards a stationary magnet the induced emf does not depend upon

1. number of turns strength of magnet
2. strength of magnet
3. speed with which the coil is moved
4. resistance of the coil

✅ Correct Answer: 4

Self-induction opposes the growth of current in a circuit when the current is

1. switched on
2. switched off
3. steady
4. fluctuating

✅ Correct Answer: 1

A cylindrical magnet is kept along the axis of a circular coil In rotating the magnet about its axis the coil will have induced in it

1. current
2. no current
3. only an e. m. f.
4. both e. m. f. and current

✅ Correct Answer: 2

A generator produces 22 KW of power at 100 A at 220 V. The length of transmission line is 100 Kilometre whose resistance is 1 ohm. The line loss will be

1. 5 kW
2. 10 kW
3. 15 kW
4. 20 kW

✅ Correct Answer: 2

Self-inductance is measured in

1. ohms
2. amperes
3. volt
4. henry

✅ Correct Answer: 4

A step up transformer is used on 120 V line to provide a P. D. of 2400 V. If the number of turns is 75 then the number of turns in the secondary shall be

1. 25
2. 150
3. 1500
4. 500

✅ Correct Answer: 3

A power transmission line feed input power at 2200 V to a step down transformer with its primary windings having 3000 turns in secondary windings should be

1. 400
2. 200
3. 500
4. 300

✅ Correct Answer: 4