Physics Past Questions and Answers

in a pure semiconductor, the number of electrons in the conduction band is

A Less than the number of holes in the valence band
B Equal to the number of holes in the valence band
C Greater than the number of holes in the valence band
D Twice the number of holes in the valence band

Question 27:

In a thermonuclear reaction, the total initial mass is 5.02 x \(10^{-{2}{7}}\)kg and the total final mass is 5.01 x \(10^{-{2}{7}}\)kg. The energy released in the process is
[c = 3.0 x \(10^8\) ms-1]

A 9.0 x 10^-13J
B 9.0 x 10^-12J
C 9.0 x 10^-11J
D 9.0 x 10^-10J

Question 28:

A gas would serve as an electrical conductor under

A Reduced pressure and high current
B Increased magnetic field
C Reduced pressure and reduced potential
D Exposure to visible light

Question 29:

An electric generator with a power output of 3.0KW at a voltage of 1.5KV distributes power along cables of resistance 20.0â„¦. The power loss in the cables is

A 80.0W
B 40.0W
C 10.0W
D 0.1W

Question 30:

If the frequency of an emitted x-ray is 1.6 x 10¹⁶Hz, the accelerating potential is?
[e = 1.6 x 10^-19C, h = 6.63 x 10^-34Js]

A 6630.0V
B 663.0V
C 66.3V
D 6.6V