Question # 1

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

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 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

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

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

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

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

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

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

Transformer works on the principle of:

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Self-induction

Mutual induction

Back emf

None of the above

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

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

An aero plane with a wing span of 50m flies at 540km/hr. The component of the earth’s magnetic field perpendicular to the velocity of the plane is 0.2 x 10-4 Wbm-2 . The potential difference between the tips of the wings is:

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1500V

150V

15V

0.15V

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

The SI unit of induced emf is:

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Vs/ A

Tesla

Henry

Volt

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

∞

A low-loss transformer has 230V applied to the primary and gives 4.6V in the secondary. Secondary is connected to a load which draws 5A of current. The current in the primary is:

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0.1A

1A

10A

250A

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