Question # 1

The primary and secondary coils of a transformer are linked

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Electrically

Magnetically

Are not linked at all

Frequency of A.C. used in Pakistan is:

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100 CPs

60 CPs

50 CPs

120 CPs

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

If the magnetic flux linked with a coil varies at the rate of 1wb/min, the induced emf is:

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1V

1/60V

60V

None of these

Transformer obeys the law of conservation of:

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Flux

Momentum

Power

emf

The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns The primary is connected to an a.c supply of 20V,50Hz. The secondary will have an output of

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2V, 50Hz

200V, 500Hz

200V, 50Hz

2V, 5Hz

Lenz’s law deals with the:

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Magnetic field of emf

Direction of emf

Both of the magnitude and direction of emf

Direction of induced current

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

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

Direction of induced current always:

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Oppose the cause

Remains same as that of cause

equal to cause that produces it

Directs the cause

The magnitude of emf of a conductor of length L and velocity V is equal to:

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VB/ L

VL/ B

VBL

qVBL

As per Faraday’s laws of electromagnetic induction, an e.m.f is induced in a conductor whenever it:

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Lies perpendicular to the magnetic field

Cuts magnetic field

Lies in a magnetic field

Moves parallel to the direction of the magnetic field

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

A transformer is used to light a 100 W, 110 V lamp from a 220V supply. If the supply current is 0.5A, the efficiency of the transformer is:

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30%

50%

80%

90%

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

Which one of the following does not effect the magnitude of the induce emf inelectromagnetic induction?

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The strength of the magnetic field linkage the cell

The resistance of the coil cutting the magnetic field

The speed with which the coil cuts the magnetic field

The number of turns in the 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

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

A magnet is allowed to fall through a metal ring. Its acceleration A), during the fall is:

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a < g

a > g

a = g

a = 0

A step-up transformer

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Increases power-leve

Increases voltage -level

Decreases current -level

Both B and C

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