Electric Charges and Fields — Physics STD 12 Science — Question

In  nucleus, there are

(a) 138 protons and 88 neutrons	(b) 138 neutrons and 88 protons
(c) 226 protons and 88 electrons	(d) 226 neutrons and 138 electrons

At any instant the ratio of the amount of radioactive substances is 2 : 1. If their half lives be respectively 12 and 16 hours, then after two days, what will be the ratio of the substances

(a) 1 : 1

(b) 2 : 1

(c) 1 : 2

(d) 1 : 4

A closely wound flat circular coil of 25 turns of wire has diameter of 10 cm and carries a current of 4 ampere. Determine the flux density at the centre of a coil

(a) 1.679	(b) 2.028
(c) 1.257	(d) 1.512

If the potential difference applied to the tube is doubled and the separation between the filament and the target is also doubled, the cutoff wavelength:

Out of the following which one is not a possible energy for a photon to be emitted by hydrogen atom according to Bohr’s atomic model?

Is the ratio of frequencies of UV rays and IR rays in the glass more than, less than or equal to 1?

The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be

(a)

(b) L

(c) 4 L

(d) 16 L

An element X has mass number 10, and number of neutrons = 7. Then what will be the number of proton?

Force of attraction between two point charges Q and -Q separated by d metre is . When these charges are placed on two identical spheres of radius R = 0.3d whose centres are d metre apart, the force of attraction between them is

(a) Greater than

(b) Equal to

(c) Less than

(d) Less than

Three long, straight parallel wires carrying current, are arranged as shown in figure. The force experienced by a 25 cm length of wire C is

(a) 10-3 N

(b) 2.5 ×10-3 N

(c) Zero

(d) 1.5 × 10-3 N