Magnetism And Matter — Physics STD 12 Science — Question

Assertion  : Television signals are received through sky-wave propagation.

Reason      :  The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Out of the following, waves of which frequency can penetrate ionosphere?

Identify the factor which does not depend on the resistance of a conductor.

What is the ratio of heat generated in R and 2R

(a) 2 : 1

(b) 1 : 2

(c) 4 : 1

(d) 1 : 4

In the given figure, an electron is moving from A to B. The direction of A induced current in the loop is:

An object is placed at a distance of 25 cm on the axis of a concave mirror, having focal length 20 cm . Find the lateral magnification of an image.

If a bar magnet of magnetic moment M is freely suspended in a uniform magnetic field of strength B, the work done in rotating the magnet through an angle θ is

(a) MB(1- sinθ

(b) MB sinθ

(c) MB cosθ

(d) MB(1 – cosθ)

The magnetic dipole moment of a current loop is independent of:

In Young's double slit experiment, if the widths of the slits are in the ratio 4 : 9, the ratio of the intensity at maxima to the intensity at minima will be

(a) 169 : 25

(b) 81 : 16

(c) 25 : 1

(d) 9 : 4

Zener breakdown in a semi-conductor diode occurs when

(a) Forward current exceeds certain value	(b) Reverse bias exceeds certain value
(c) Forward bias exceeds certain value	(d) Potential barrier is reduced to zero