JAMB Physics Past Questions & Answers - Page 160

796.

The strength of an electromagnet increases with

A.

Increases in the number of turn of the coil

B.

Decreases in current with the coil

C.

Increases in the distance between the pole

D.

Increases in current without the coil

Correct answer is A

No explanation has been provided for this answer.

797.

A radioactive source emits X–rays of very short wavelength (10 -13m ). what is the frequency of these rays?

A.

2 × 1018HZ

B.

3 × 10 19HZ

C.

3 × 1021HZ

D.

3 × 10-19HZ

Correct answer is C

\(Wavelength (\lambda) = 10^{-13}m\)

Speed of X-ray = speed of light \(C = 3×10^{8}m/s\)

Frequently (f) = ?

\(Using V = f\lambda (or (– f π for electromagnetic wave)\)

\(f = \frac{c}{\lambda} = 3 \times 10^{8} ÷ 10^{-13} = 3 \times 10^{8} \times 10^{13}\)

= \(3 \times 10^{8} \times 10^{13}\)

= \(3 \times 10^{21}Hz\)

798.

The symbol −10X used to represent which of the particles?

A.

Proton

B.

Neutron

C.

Electrons

D.

Atoms

Correct answer is C

Electron: A sub–atomic particle haring a negative charge and orbiting the nucleus (note: the symbol 0–1e represent the particle of an electrons.)

799.

The optical instrument which is suitable for viewing a nearby objects is ………..?

A.

Telescope

B.

sextant

C.

microscope

D.

periscope

Correct answer is C

Microscope is used for nearby object

800.

If an object whose mass is 3kg moves in a circular path of a radius 0.7m, records a speed at 2m/s. What is the result of the angular velocity?

A.

4 rads–1

B.

1rads–1–1

C.

3–1rads–1

D.

4rads–1–1

Correct answer is C

M= 3kg, r = 0.7m, v = 2m/s

v = wr

w = angular velocity

r = radius in an tangential circular

v = speed of an object

W = V/δ = 2/ 0.7 = 2.85

W = 2.853rads–1 (total interest whole number)

W = &approx.; 3rads–1Angular velocity (w) = 3rads–1