Magnetism And Matter — Physics STD 12 Science — Question

The combination of a convex lens (f = 18 cm) and a thin concave lens (f = 9 cm) is

(a) A concave lens (f = 18 cm)	(b) A convex lens (f = 18 cm)
(c) A convex lens (f = 6 cm)	(d) A concave lens (f = 6 cm)

A square metallic wire loop of side 0.1 m and resistance of 1W is moved with a constant velocity in a magnetic field of 2 wb/m² as shown in figure. The magnetic field is perpendicular to the plane of the loop, loop is connected to a network of resistances. What should be the velocity of loop so as to have a steady current of 1mA in loop

(a) 1 cm/sec

(b) 2 cm/sec

(c) 3 cm/sec

(d) 4 cm/sec

In the figure shown there are two semicircles of radii  and  in which a current i is flowing. The magnetic induction  at the centre O will be

(a)  (

(b)   (

(c)

(d)

The desirable properties for making permanent magnets are:

1. High retentivity and high coercive force.
2. High retentivity and low coercive force.
3. Low retentivity and high coercive force.
4. Low retentivity and low coercive force.

Work done in moving a positive charge on an equipotential surface is

(a) Finite, positive but not zero	(b) Finite, negative but not zero
(c) Zero	(d) Infinite

100 cells each of e.m.f. 5 V and internal resistance 1 ohm are to be arranged so as to produce maximum current in a 25 ohms resistance. Each row is to contain equal number of cells. The number of rows should be

(a) 2

(b) 4

(c) 5

(d) 10

Which one of the following have minimum wavelength

(a) Ultraviolet rays

(b) Cosmic rays

(c) X-rays

(d) γ - rays

The atomic number of two atoms are equal but their atomic masses are different. These will be

For total internal reflection to take place, the angle of incidence i and the refractive index μ of the medium must satisfy the inequality

(a)

(b)

(c) sin i <

(d) sin i >

Assertion  :  Different colours travel with different speed in vacuum.

Reason     : Wavelength of light depends on refractive index of medium.

(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 assertion is false but reason is true.