Electric Charges and Fields — Physics STD 12 Science — Question

A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens.  Then its focal length will

(a) Become infinite	(b) Become small, but non–zero
(c) Remain unchanged	(d) Become zero

A resistor of resistance R is connected to an ideal battery. If the value of R is decreased, the power dissipated in the resistor will:

1. Increase.
2. Decrease.
3. Remain unchanged.

In a meter bridge, the balancing length from the left end (standard resistance of one ohm is in the right gap) is found to be 20 cm. The value of the unknown resistance is

(a) 0.8 Ω

(b) 0.5 Ω

(c) 0.4 Ω

(d) 0.25 Ω

If eight identical drops are joined to form a bigger drop, the potential on bigger as compared to that on smaller drop will be

(a) Double

(b) Four times

(c) Eight times

(d) One time

A magnet makes 40 oscillations per minute at a place having magnetic field intensity of 0.1 × 10^–5 T. At another place, it takes 2.5 sec to complete one vibration. The value of earth’s horizontal field at that place is

(a) 0.25 × 10–6 T

(b) 0.36 × 10–6 T

(c) 0.66 × 10–8 T

(d) 1.2 × 10–6 T

During a nuclear fission reaction:

1. A heavy nucleus breaks into two fragments by itself a light nucleus bombarded by thermal neutrons breaks up.
2. A light nucleus bombarded by thermal neutrons breaks up.
3. A heavy nucleus bombarded by thermal neutrons breaks up.
4. Two light nuclei combine to give a heavier nucleus and possible other products.

The ratio of the frequencies of the long wavelength limits of Lyman and Balmer series of hydrogen spectrum is

(a) 27 : 5

(b) 5 : 27

(c) 4 : 1

(d) 1 : 4

Which of the planet is brightest

(a) Mercury

(b) Venus

(c) Mars

(d) Jupiter

In P-type semiconductor the majority and minority charge carriers are respectively

(a) Protons and electrons	(b) Electrons and protons
(c) Electrons and holes	(d) Holes and electrons

The de Broglie wavelength associated with a ball of mass 150g travelling at 30 ms⁻¹ is: