Ray Optics and Optical Instruments — Physics STD 12 Science — Question

A magnet of magnetic moment M is rotated through 360° in a magnetic field H, the work done will be

(a) MH

(b) 2MH

(c) 2πMH

(d) Zero

A charge of 5C  experiences a force of 5000 N when it is kept in a uniform electric field. What is the potential difference between two points separated by a distance of 1 cm

(a) 10 V

(b) 250 V

(c) 1000 V

(d) 2500 V

The electron in a hydrogen atom makes a transition , where   and  are the principal quantum numbers of the two states. Assume the Bohr model to be valid. The time period of the electron in the initial state is eight times that in the final state. The possible values of n₁ and n₂ are

(a)

(b)

(c)

(d)

An electromagnetic waves can be produced, when charge is:

When a certain length of wire is turned into one circular loop, the magnetic induction at the centre of coil due to some current flowing is  If the same wire is turned into three loops to make a circular coil, the magnetic induction at the center of this coil for the same current will be

(a)

(b) 9

(c) 3

(d) 27

A hollow copper sphere A and a solid sphere B of equal radius are charged with the same potential. The true statement is:

For a thermocouple the neutral temperature is 270℃  when its cold junction is at 20℃. What will be the neutral temperature and the temperature of inversion when the temperature of cold junction is increased to 40 ℃

(a) 290℃, 580℃

(b) 270℃, 580℃

(c) 270℃, 500 ℃

(d) 290 ℃, 540 ℃

The wavelength 21 cm emitted by atomic hydrogen in interstellar space belongs to

(a) Radio waves

(b) Infrared waves

(c) Microwaves

(d) g-rays

Three observers A, B and C measure the speed of light coming from a source to be vA, 0B and vc. The observer A moves towards the source and C moves away from the source at the same speed. The observer B stays stationary. The surrounding space is vacuum everywhere.

Two infinitely long parallel wires carry equal current in same direction. The magnetic field at a mid point in between the two wires is

(a) Twice the magnetic field produced due to each of the wires

(b) Half of the magnetic field produced due to each of the wires

(c) Square of the magnetic field produced due to each of the wires

(d) Zero