Question # 1

A coil having 500 square loops, each of the side 10cm is placed normal to a magnetic field which increased at the rate 1T/sec. The emf induced is:

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0.1V

0.5V

1V

5V

In a transformer, the immediate cause of the induced alternating current in the secondary coil is:

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a varying magnetic field

a varying electric field

the iron core of the transformer

a motion of the primary coil

When a transformer is used to stepping up A.C voltage from 100 V to 200 V is connected across 50V D.C mains, then:

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Output voltage is 100 V

Output voltage is 250 V

No voltage is developed across the secondary

None of these

Identify the phenomenon by which an induced emf could be generated:

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By moving a conductor across a magnetic field

By rotating a coil faster through the field

By increasing the strength

All the above

Transformer obeys the law of conservation of:

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Flux

Momentum

Power

emf

Transformer works on the principle of:

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Self-induction

Mutual induction

Back emf

None of the above

A step-up transformer

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Increases power-leve

Increases voltage -level

Decreases current -level

Both B and C

The north pole of a bar magnet is rapidly introduced into a solenoid from its end P. Which of the following statements correctly depicts the phenomenon taking place?

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No induced emf is set up.

The end P of the solenoid behaves like a north pole.

None of the above

The average value of A.C. current and voltage over a complete cycle is:

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Maximum

Zero

Neither zero nor maximum

None of the above

The loss of power in transformer occurs due to:

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The shape of coils

Size of coils

Magnetic hysteresis and Eddy current

None of these

During each cycle, alternating voltage reaches a peak value:

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One time

Two time

Four-time

A number of times depending on the frequency

The primary and secondary coils of a transformer are linked

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Electrically

Magnetically

Are not linked at all

In general, in an ac circuit:

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The average value of current is zero

The average value of the square of the current is zero

The average power dissipation is zero

The phase difference between voltage and current is zero

When the power output in watts equals one half the power input, the efficiency of the transformer becomes:

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100%

200%

50%

Zero

The SI unit of induced emf is:

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Vs/ A

Tesla

Henry

Volt

Why does a transformer have a core made of iron

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iron has a high melting point

iron is a conductor of head

iron is a conductor of electricity

iron is a magnetic material

A step-up transformer operates on 230V line and supplies a load of 2A. The ratio of primary and secondary turns is 1:25. The current in the primary is:

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50A

25A

15A

12.5A

In the step up transformer, when the alternating voltage increase then the alternating current will

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Increase

Decrease

not change

Not depend on core

When no power is drawn in the secondary coil of an ideal transformer, the power of the primary coil of an ideal transformer, is:

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one

zero

½

∞

Lenz law is in accordance with the law of conservation of:

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Momentum

Angular momentum

Charge

Energy

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