Question # 1

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

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Momentum

Angular momentum

Charge

Energy

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

The SI unit of induced emf is:

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Vs/ A

Tesla

Henry

Volt

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%

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 step-up transformer

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Increases power-leve

Increases voltage -level

Decreases current -level

Both B and C

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

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 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

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

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

∞

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

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

Transformer obeys the law of conservation of:

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Flux

Momentum

Power

emf

Such a value A.C current which produces the same heating effect as is produced by the D.C of equal magnitude is called:

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r.m.s current

Peak current

Effective current

None of the above

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

In a transformer, the number of primary coil and secondary coil are 5 and 4 respectively. If 240 V is applied on the primary coil, then the ratio of current in primary and secondary coil is:

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4:5

5:4

5:9

9:5

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

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 motional of emf depends upon the:

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Length of conductor

Strength of magnetic field

Speed of conductor

All the above

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