JAMB Physics Past Questions & Answers - Page 455

2,272.

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

Correct answer is A

In general, gases conduct electricity under reduced pressure and high voltage/potential.

But from Ohms Law, current is directly proportional to voltage. Thus high current presupposes high voltage.

2,273.

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

Correct answer is A

In thermonuclear reactions,
Energy = ∆mC2
∆m = Change in Mass
C = Speed of light
∴ 5.02 x 10-27 - 5.01 x 10-27 x [3 x 108]2
0.01 x 10-27 x 9 x 1016
E = 9.0 x 10-13J

2,274.

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

Correct answer is B

No explanation has been provided for this answer.

2,275.

What optical instrument can best be constructed with converging lenses of focal lengths 50cm and 5cm?

A.

Compound microscope

B.

Galileo's telescope

C.

Terrestrial telescope

D.

Astronomical telescope

Correct answer is D

No explanation has been provided for this answer.