SSC JE 2014 Electrical question paper with solution(Evening-shift)

When the north pole of the magnet is moved away from the coil the direction of the induced current is such as to make the nearer pole of the coil a south pole which makes clockwise induced current flow in the coil or the ring.

The energy stored in the magnetic field of an inductor can be expressed as

W = 1/2 L I²

where

W = energy stored (joules, J)

L = inductance (henrys, H)

I = current (amps, A)

The self inductance of a solenoid is given as

L = μN²A/I = L1

where

N is the number of turns of the solenoid

A is the area of each turn of coil

l is the length of the solenoid

and μ is the permeability constant

so, if the number of turns was to be doubled the self-inductance would be

L2 = u (2N)²A/l

or

L2 = 4L1

it would be quadrupled or increased fourfold.

The phenomenon of flux density B lagging behind the magnetizing force H in a magnetic material is known as Magnetic Hysteresis.

Induced EMF E is

E = NdΦ/dt

The self induced EMF is given as

E = Ldi/dt

= 2 × 10

= 20 V

The amount of magnetic field we apply, air never saturates. So the B-H curve in the air should be a straight line

Air is non-magnetic material and for non-magnetic material, the B =µoH and since µo = 4π x 10-7  is a constant quantity, therefore, B ∝ H

The two magnetic field lines do not intersect each other because If the lines intersected, then at the point of intersection there would be two directions of magnetic field force which means at the point of intersecting the compass needle is showing two different directions which is not possible.

Magnets have two regions called magnetic poles with magnetism both in and around a magnetic circuit generating an invisible line of flux around it. These lines of flux are referred to as the “magnetic field” of the magnet.

Soft magnets are temporary – they only produce magnetic fields while an external magnetic field is present and lose nearly all their magnetism once the external field is removed. Hence the magnetic flux can be changed in temporary magnets.

The permanent magnet is made of hardened steel because soft iron and steel remain magnets only under the power or influence of other magnets and lose their magnetism as soon as the magnet is removed.

Compared to iron, steel cannot be easily demagnetized or magnetized. It can only be magnetized under the influence of a strong magnetic field. But steel has the ability to retain its magnetism once it is magnetized. Therefore steel is best suited to be used in permanent magnets.