Physics M.C.Q (1 Marks)

In a lossless transformer an alternating current of  2 amp is flowing in the primary coil. The number of turns in the primary and secondary coils are 100 and 20 respectively. The value of the current in the secondary coil is(a) 0.08 A(b) 0.4 A(c) 5 A(d) 10 A

The coils of a step down transformer have 500 and 5000 turns. In the primary coil an ac of 4 ampere at 2200 volts is sent. The value of the current and potential difference in the secondary coil will be(a) 20 A, 220 V(b) 0.4 A, 22000 V(c) 40 A, 220 V(d) 40 A, 22000 V

The efficiency of transformer is very high because(a) There is no moving part in a transformer(b) It produces very high voltage(c) It produces very low voltage(d) None of the above

A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 amp, then the current in the primary coil is(a) 1 amp (b) 4 amp(c) 8 amp (d) 16 amp

We can reduce eddy currents in the core of transformer(a) By increasing the number of turns in secondary coil(b) By taking laminated core(c) By making step-down transformer(d) By using a weak ac at high potential

In transformer, core is made of soft iron to reduce(a) Hysteresis losses(b) Eddy current losses(c) Force opposing electric current(d) None of the above

A transformer is employed to(a) Obtain a suitable dc voltage(b) Convert dc into ac(c) Obtain a suitable ac voltage(d) Convert ac into dc

The alternating voltage induced in the secondary coil of a transformer is mainly due to(a) A varying electric field(b) A varying magnetic field(c) The vibrations of the primary coil(d) The iron core of the transformer

In a step-up transformer, the turn ratio is 1 : 2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary. The voltage developed in the secondary would be(a) 3.0 V(b) 0.75 V(c) 1.5 V  (d) Zero

A transformer is employed to reduce 220 V to 11 V. The primary draws a current of 5 A and the secondary 90 A. The efficiency of the transformer is(a) 20%(b)  40%(c) 70%(d)  90%

In a transformer 220 ac voltage is increased to 2200 volts. If the number of turns in the secondary are 2000, then the number of turns in the primary will be(a) 200(b) 100(c) 50       (d) 20

The core of a transformer is laminated so that(a) Ratio of voltage in the primary and secondary may be increased(b) Rusting of the core may be stopped(c) Energy losses due to eddy currents may be reduced(d) Change in flux is increased

What is increased in step-down transformer(a) Voltage(b)  Current(c) Power  (d) Current density

A motor having an armature of resistance 2Ω is designed to operate at 220 V mains. At full speed, it develops a back e.m.f. of 210V. When the motor is running at full speed, the current in the armature is(a) 5A      (b) 105A(c) 110A  (d) 215A

An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the ac is 28 V. The r.m.s. secondary voltage is nearest to(a) 50 V(b) 70 V(c) 100 V (d) 40 V

A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be (a) 1600 A(b) 20 A(c) 4 A(d) 1.5 A

The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an ac supply of 120 V and the current flowing in it is 10 A. The voltage and the current in the secondary are(a) 240 V, 5 A(b) 240 V, 10 A(c) 60 V, 20 A(d) 120 V, 20 A

An electric motor operates on a 50 volt supply and a current of 12A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor(a) 6 Ω(b) 4 Ω(c) 2.9 Ω(d) 3.1 Ω

A device which converts electrical energy into mechanical energy is(a) Dynamo(b) generator(c) Electric motor(d) Induction coil

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is(a) 3Ω(b) 6 Ω(c) 15 Ω(d) 30 Ω

Work of electric motor is(a) To convert ac into dc(b) To convert dc into ac(c) Both (a) and (b)(d) To convert ac into mechanical work

Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be

In a dc motor, induced e.m.f. will be maximum(a) When motor takes maximum speed(b) When motor starts rotating(c) When speed of motor increases(d) When motor is switched off

In an induction coil, the secondary e.m.f. is(a) Zero during break of the circuit(b) Very high during make of the circuit(c) Zero during make of the circuit(d) Very high during break of the circuit

Eddy currents are produced when(a) A metal is kept in varying magnetic field(b) A metal is kept in the steady magnetic field(c) A circular coil is placed in a magnetic field(d) Through a circular coil, current is passed

Armature current in dc motor will be maximum when(a) Motor has acquired maximum speed(b) Motor has acquired intermediate speed(c) Motor has just started moving(d) Motor is switched off

Dynamo core is laminated because(a) Magnetic field increases(b) Magnetic saturation level in core increases(c) Residual magnetism in core decreases(d) Loss of energy in core due to eddy currents decreases

The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following condition is correct(a) Lines of force minimum but induced e.m.f. is zero(b) Lines of force maximum but induced e.m.f. is zero(c) Lines of force maximum but induced e.m.f. is not zero(d) Lines of force maximum but induced e.m.f. is also maximum

Which of the following statement is incorrect(a) Both ac and dc dynamo have a field magnet(b) Both ac and dc dynamo have an armature(c) Both ac and dc dynamo convert mechanical energy into electrical energy(d) Both ac and dc dynamo have slip rings

The output of a dynamo using a splitting commutator is(a) dc(b) ac(c) Fluctuating dc(d) Half-wave rectified voltage

When the speed of a dc motor increases the armature current(a) Increases(b) Decreases(c) Does not change(d) Increases and decreases continuously

Choke coil works on the principle of(a) Transient current(b)  Self induction(c) Mutual induction(d) Wattless current

The working of dynamo is based on principle of(a) Electromagnetic induction(b) Conversion of energy into electricity(c) Magnetic effects of current(d) Heating effects of current

Dynamo is a device for converting(a) Electrical energy into mechanical energy(b) Mechanical energy into electrical energy(c) Chemical energy into mechanical energy(d) Mechanical energy into chemical energy

The armature of dc motor has 20Ω resistance. It draws current of 1.5 ampere when run by 220 volts dc supply. The value of back e.m.f. induced in it will be(a) 150 V(b) 170 V(c) 180 V (d) 190 V

If rotational velocity of a dynamo armature is doubled, then induced e.m.f. will become(a) Half(b) Two times(c) Four times(d) Unchanged

If the current 30 A flowing in the primary coil is made zero in 0.1 sec. The emf induced in the secondary coil is 1.5 volt. The mutual inductance between the coil is(a)  0.05 H(b)  1.05 H(c)  0.1 H(d)  0.2 H    

The device that does not work on the principle of mutual induction is(a) Induction coil(b) Motor(c) Tesla coil(d) Transformer

The pointer of a dead-beat galvanometer gives a steady deflection because(a) Eddy currents are produced in the conducting frame over which the coil is wound(b) Its magnet is very strong(c) Its pointer is very light(d) Its frame is made of abonite

The core of a transformer is laminated to reduce energy losses due to(a) Eddy currents(b) Hysteresis(c) Resistance in winding(d) None of these

Which of the following is not an application of eddy currents(a) Induction furnace(b) Galvanometer damping(c) Speedometer of automobiles(d) X-ray crystallography

Use of eddy currents is done in the following except(a)  Moving coil galvanometer(b)  Electric brakes(c)  Induction motor(d)  Dynamo

Plane of eddy currents makes an angle with the plane of magnetic lines of force equal to(a) 40°(b) 0°(c) 90°(d) 180°

Which of the following is constructed on the principle of electromagnetic induction (a)  Galvanometer(b) Electric motor(c)  Generator(d) Voltmeter