Atoms — Physics STD 12 Science — Question

A charged conducting sphere does not produce an electric field:

A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from the centre of the coil, such that r >> R, varies as

(a)

(b)

(c)

(d)

A semiconductor is doped with a donor impurity:

1. The hole concentration increases.
2. The hole concentration decreases.
3. The electron concentration increases.
4. The electron concentration decreases.

An example of a diamagnetic substance is

(a) Aluminium

(b) Copper

(c) Iron

(d) Nickel

Light waves producing interference have their amplitudes in the ratio 3 : 2. The intensity ratio of maximum and minimum of interference fringes is

(a) 36 : 1

(b) 9 : 4

(c) 25 : 1

(d) 6 : 4

A point source of light is placed 4 m below the surface of water of refractive index 5 / 3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut–off all light coming out of water is

(a) 2 m

(b) 6 m

(c) 4 m

(d) 3 m

There are two metallic spheres of same radii, but one is solid, and the other is hollow, then:

If a positive charge is taken from a region of lower potential to a region of higher potential, then the electrical potential energy:

What is the unit of magnetic flux?

The distance of the eye-lens from the retina is x. For a normal eye, the maximum focal length of the eye-lens:

1. = x.
2. < x.
3. > x.
4. = 2x.