Physics [2 Mark Question Answer]

Magnitude of induced e.m.f depend upon:
(i) The change in the magnetic flux.
(ii)The time in which the magnetic flux changes.

Magnitude of induced e.m.f depend upon:
(i) The change in the magnetic flux.
(ii) The time in which the magnetic flux changes.

The secondary windings of a transformer in which the voltage is stepped down are usually made up of thicker than the primary because more current flows in the secondary coil. The use of thicker wire reduces its resistance and therefore the loss of energy as heat in the coil.

Faraday's formulated two laws of electromagnetic induction:

(i) Whenever there is a change in the magnetic flux linked with a coil, an e.m.f. is induced. The induced e.m.f. lasts so long as there is a change in the magnetic flux linked with the coil.

(ii) The magnitude of the e.m.f. induced is directly proportional to the rate of change of the magnetic flux linked with the coil. If the rate of change of magnetic flux remains uniform, a steady e.m.f. is induced.

The magnitude of an induced e.m.f. in the secondary coil of a transformer depends on the following two factors.

a) The ratio of number of turns in the secondary coil to the number of turns in the primary coil.

b) The magnitude ofm.f. applied in the primary coil.

Two ways in an a.c generator to produce a higher e.m.f. are:
(1) By increasing the speed of rotation of the coil.
(2) By increasing the number of turns of coil.

(a)In an a.c generator, if the speed at which the coil rotates is doubled, the frequency is also doubled.
(b) Maximum output voltage is also doubled.

(i) When plane of a oil is parallel to the magnetic field,

(ii) When plane of coil is normal to the magnetic field.

The speed of rotation of an electric motor can be increased by:
(i) Increasing the strength of current.
(ii) Increasing the number of turns in the coil.

Solution is as follow:

A current carrying conductor produces a magnetic field around it and the magnetic needle in this magnetic field experience a torque due to which it deflects to align itself in the direction of magnetic field.

(a) The direction of magnetic field at a point just underneath is towards east.
(b) Right hand thumb rule.

If an a.c. source is used in place of battery, the core of electromagnet will get magnetized, but the polarity at its ends will change. Since attraction of armature does not depend on the polarity of electromagnet, so the bell will still ring on pressing the switch.

The soft iron bar acquires the magnetic properties only when an electric current flows through the solenoid and loses the magnetic properties as the current is switched off. That's why soft iron is used as the core of the electromagnet in an electric bell.

1. An electromagnet can produce a strong magnetic field.
2. The strength of the magnetic field of an electromagnet can easily be changed by changing the current in its solenoid.

The magnetic field due to a solenoid can be made stronger by using:
(i) By increasing the number of turns of winding in the solenoid.
(ii) By increasing the current through the solenoid.

(a) A - North pole, B - South pole.
(b) The north pole of compass needle will deflect towards west.
Reason: The end A of the coil behaves like north pole which repels north pole of compass needle towards west.

>(a) A - North pole, B - South pole. >(b) The magnet will be repelled because the end of the solenoid near the north pole of magnet becomes the north pole as current at this face is anticlockwise and the two like poles repel.

Right hand thumb rule: If we hold the current carrying conductor in right hand such that the thumb points in the direction of flow of current, then the fingers encircle the wire in the direction of the magnetic fields lines.