Electric Charges and Fields — Physics STD 12 Science — Question

A uniform spherical shell gradually shrinks maintaining its shape. The gravitational potential at the centre:

1. Increases.
2. Decreases.
3. Remains constant.
4. Oscillates.

The force which a magnet exerts on iron and steel is called the:

The figure shows a graph between ln  and ln|n|, where   is the area enclosed by the nth orbit in a hydrogen like atom. The correct curve is

(a) 4

(b) 3

(c) 2

(d) 1

Assertion   :   A metallic shield in form of a hollow shell may be built to block an electric field.

Reason       : In a hollow spherical shield, the electric field inside it is zero at every point.

(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.

The refractive indices of water and glass with respect to air are 1.2 and 1.5 respectively. The refractive index of glass with respect to water is

(a) 0.6

(b) 0.8

(c) 1.25

(d) 1.75

The velocity factor of a transmission line x. If dielectric constant of the medium is 2.6, the value of x is

(a) 0.26

(b) 0.62

(c) 2.6

(d) 6.2

Energy bands in solids are a consequence of

(a) Ohm’s Law	(b) Pauli’s exclusion principle
(c) Bohr’s theory	(d) Heisenberg’s uncertainty principle

Zener diode works on:

In an electron gun, the electrons are accelerated by the potential V.  If e is the charge and m is the mass of an electron, then the maximum velocity of these electrons will be

(a)

(b)

(c)

(d)