In the relation \(\phi \) = BA cos \(\theta \), \(\theta \) is angle........

1

(a)

which normal to surface area makes with the direction of magnetic field

(b)

which magnetic field makes with the surface

(c)

which is never constant

(d)

none of the above

Which one is not an application of eddy currents?

1

(a)

Magnetic brakes

(b)

speedometers

(c)

Induction furnace

(d)

Transformers

Phase difference between voltage across L and C in series is

1

(a)

\({ 0 }^{ \circ }\)

(b)

\({9 0 }^{ \circ }\)

(c)

\({180 }^{ \circ }\)

(d)

\({ 360 }^{ \circ }\)

The frequency of a.c. generated depends on

1

(a)

speed of rotation of coil

(b)

amplitude of a.c

(c)

size of coil

(d)

all the above

The form factor of an a.c. generated is given by

1

(a)

\(\frac { { I }_{ av } }{ { I }_{ 0 } } \)

(b)

\(\frac { { I }_{ 0 } }{ { I }_{ av } } \)

(c)

\(\frac { { I }_{ av } }{ { I }_{ v } } \)

(d)

\(\frac { { I }_{ v } }{ { I }_{ av } } \)

A vertical metallic pole falls down through the plane of magnetic meridian. Will any e.m.f. be induced between its ends ?

1

(a)

No, because the pole intercepts neither H nor V.

The induced e.m.f. is sometimes called back e.m.f. Why ?

1

(a)

This is because induced e.m.f. opposes the current due to the actual source e.m.f.

Why are oscillations of a copper sheet in a magnetic field highly damped ?

1

(a)

This is because of eddy currents developed in copper sheet.

What causes sparking in the switches when light is put off ?

1

(a)

Large induced e.m.f. at break causes the sparking.

What is the basic cause of induced e.m.f.?

1

(a)

Change in magnetic flux linked with the circuit

An artificial satellite with a metal surface is orbiting the earth around the poles. Will there be any induced current due to earth's magnetic field ?

2

(a)

A circular brass loop of radius a and resistance R is placed with its plane perpendicular to a magnetic field, which varies with time as \(B={ B }_{ 0 }sin\omega t.\) Obtain the expression for the induced current in the loop.

2

(a)

Can one have an inductance without a resistance ? How about a resistance with an inductance?

2

(a)

Define the term self-inductance of a solenoid. Obtain the expression for the magnetic energy stored in an inductor of self-inductance L to build up a current I through it.

3

(a)

The current, in the LCR circuit shown in the figure, is observed to lead the voltage in phase. Without making any other change in the circuit, a capacitor, of capacitance C_o' is (appropriately) joined to the capacitor C_o. This results in making the current, in the 'modified' circuit, flow in phase with the applied voltage. Draw a diagram of the 'modified' circuit and obtain an expression for C_o in terms of \(\omega \) L and C

3

(a)