Magnetism And Matter — Physics STD 12 Science — Question

The desirable properties for making permanent magnets are:

A hollow double concave lens is made of very thin transparent material.  It can be filled with air or either of two liquids L₁ and L₂ having refractive indices n₁ and n₂ respectively (n₂ > n₁ > 1).  The lens will diverge a parallel beam of light if it is filled with

(a) Air and placed in air	(b) Air and immersed in L1
(c) L1 and immersed in L2	(d) L2 and immersed in L1

In Fresnel diffraction, if the distance between the disc and the screen is decreased, the intensity of central bright spot will

(a) Increase

(b) Decrease

(c) Remain constant

(d) None of these

Which of the following quantities is zero on an average for the molecules of an ideal gas in equilibrium?

1. Kinetic energy.
2. Momentum.
3. Density.
4. Speed.

A rectangular coil 20 cm × 20 cm  has 100 turns and carries a current of 1 A. It is placed in a uniform magnetic field       B  = 0.5 T with the direction of magnetic field parallel to the plane of the coil. The magnitude of the torque required to hold this coil in this position is

(a) Zero

(b) 200 N-m

(c) 2 N-m

(d) 10 N-m

In X-ray experiment K_a, K_b denotes

(a) Characteristic	(b) Continuous wavelength
(c) a, b-emissions respectively	(d) None of these

When a plane polarised light is passed through an analyser and analyser is rotated through 90°, the intensity of the emerging light

(a) Varies between a maximum and minimum

(b) Becomes zero

(c) Does not vary

(d) Varies between a maximum and zero

Three positive charges of equal value q are placed at the vertices of an equilateral triangle. The resulting lines of force should be sketched as in

(a)

(b)

(c)

(d)

The valence band and conduction band of a solid overlap at low temperature, the solid may be

(a) A metal

(b) A semiconductor

(c) An insulator

(d) None of these

A horizontal circular loop carries a current that looks clockwise when viewed from above. It is replaced by an equivalent magnetic dipole consisting of a south pole S and a north pole N:

1. The line SN should be along a diameter of the loop.
2. The line SN should be perpendicular to the plane of the loop.
3. The south pole should be slow the loop.
4. The north pole should be below the loop.