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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Electromagnetic waves are transverse in nature is evident by:

1.polarization

2.interference

3.reflection

4.diffraction

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

1.180v

2.200v

3.220v

4.none of these

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

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

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

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

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

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

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

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

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

1.LR

2.R/L

3.L/R

4.1/LR

In LR circuit the time constant is given by

1.LR

2.R / L

3.L / R

4.1 / LR

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

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

1.Ohm

2.A-F

3.Ohm-m

4.sec

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

Induction coil is based on the principle of

1.rheostate

2.self induction

3.mutual induction

4.induction

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

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

Self-inductance is measured in

1.ohms

2.amperes

3.volt

4.henry

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

1.switched on

2.switched off

3.steady

4.fluctuating

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

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

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

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

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

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

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

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

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

The reactance of an inductor connected with DC voltage is:

1.zero

2.infinity

3.1?

4.none of these

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

The time constant of C-R circuit is:

1.1/CR

2.C/R

3.CR

4.R/C

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

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

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

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

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

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

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

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

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