Electric Charges and Fields — Physics STD 12 Science — Question

An oxide coated filament is useful in vacuum tubes because essentially

(a) It has high melting point

(b) It can withstand high temperatures

(c) It has good machanical strength

(d) It can emit electrons at relatively lower temperatures

Which among the following cannot be the charge of a charged body?

Two lenses having   has combination to make no dispersion. Find the ratio of dispersive power of glasses used

(a) 2 :  3

(b) 3 : 2

(c) 4 : 9

(d) 9 : 4

Consider the motion of the tip of the minute hand of a clock. In one hour:

1. The displacement is zero.
2. The distance covered is zero.
3. The average speed is zero.
4. The average velocity is zero.

Sky wave propagation is based on :

Positive rays was discovered by

(a) Thomson

(b) Goldstem

(c) W. Crookes

(d) Rutherford

M_x and M_y denote the atomic masses of the parent and the daughter nuclei respectively in a radioactive decay. The Q-value for a β^- decay is Q₁ and that for a β⁺ decay is Q₂. If me denotes the mass of an electron, then which of the following statements is correct?

The narrowest hysterisis loop is for:

The ratio of thickness of plates of two transparent mediums A and B is 6 : 4.  If light takes equal time in passing through them, then refractive index of B with respect to A will be

(a) 1.4

(b) 1.5

(c) 1.75

(d) 1.33

The mass number of a nucleus is equal to:

1. The number of neutrons in the nucleus.
2. The number of protons in the nucleus.
3. The number of nucleons in the nucleus.
4. None of them.