Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

When an atomic gas or vapour is excited at low pressure, by passing an electric current through it then?

Electric charges of +10μC, + 5μC, -3μC and +8 μC  are placed at the corners of a square of side  m. the potential at the centre of the square is

(a) 1.8 V

(b)  V

(c) 1.8

(d) 1.8  V

Half-life of a radioactive substance is 20 minutes. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately

(a) 10 min

(b) 20 min

(c) 30 min

(d) 40 min

A gamma ray photon creates an electron- positron pair. If the rest mass energy of an electron is 0.5 MeV and the total K.E. of the electron- positron pair is 0.78 MeV, then the energy of the gamma ray photon must be

(a) 0.78 MeV

(b) 1.78 MeV

(c) 1.28 MeV

(d) 0.28 MeV

A triangular loop of side l carries a current I. It is placed in a magnetic field B such that the plane of the loop is in the direction of B. The torque on the loop is

(a) Zero

(b) IBl

(c)

(d)

The charge is negative, then the electric lines of forces are:

The time period of oscillation of a magnet in a vibration magnetometer is 1.5 seconds. The time period of oscillation of another magnet similar in size, shape and mass but having one-fourth magnetic moment than that of first magnet, oscillating at same place will be

(a) 0.75 sec

(b) 1.5 sec

(c) 3 sec

(d) 6 sec

A ray of light passes through an equilateral glass prism in such a manner that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of the angle of the prism. The angle of deviation is

(a) 45°

(b) 39°

(c) 20°

(d) 30°