Electric Charges and Fields — Physics STD 12 Science — Question

In a laboratory experiment on emission from atomic hydrogen in a discharge tube, only a small number of lines are observed whereas a large number of lines are present in the hydrogen spectrum of a star. This is because in a laboratory:

1. The amount of hydrogen taken is much smaller than that present in the star.
2. The temperature of hydrogen is much smaller than that of the star.
3. The pressure of hydrogen is much smaller than that of the star.
4. The gravitational pull is much smaller than that in the star.

Two electric charges 12μC and -6 μC  are placed 20 cm apart in air. There will be a point P on the line joining these charges and outside the region between them, at which the electric potential is zero. The distance of P from -6 μC  charge is

(a) 0.10 m

(b) 0.15 m

(c) 0.20 m

(d) 0.25 m

Displacement current is continuous:

Diffusion current in a p-n junction is greater than the drift current in magnitude:

n identical bulbs, each designed to draw a power p from a certain voltage supply, are joined in series across that supply. The total power which they will draw is

(a)

(b) p/n

(c) p

(d) np

Three long, straight and parallel wires carrying currents are arranged as shown in figure. The force experienced by 10 cm length of wire Q is

(a) 1.4  towards the right	(b) 1.4  towards the left
(c) 2.6  to the right	(d) 2.6  to the left

A circular loop carrying a current is replaced by an equivalent magnetic dipole. A point on the loop is in:

Four cylinders contain equal number of moles of argon, hydrogen, nitrogen and carbon dioxide at the same temperature. The energy is minimum in:

1. Argon.
2. Hydrogen.
3. Nitrogen.
4. Carbon dioxide.