WAEC Past Questions and Answers - Page 4025

20,121.

I Electrical potential,
II Torque,
III Kinetic Energy,
IV Momentum.

Which of the quantities listed are vectors?

A.

II and IV

B.

I and II

C.

I and III

D.

II and III

Correct answer is A

No explanation has been provided for this answer.

20,122.

A quantity which requires magnitude and direction to be specified is

A.

Temperature

B.

Distance

C.

Displacement

D.

Mass

Correct answer is C

Displacement is a vector quantity

20,123.

What is the least possible error encountered when taking measurement with a meter rule?

A.

0.1mm

B.

1.0mm

C.

0.5mm

D.

0.2mm

Correct answer is C

No explanation has been provided for this answer.

20,124.

A circle has radius x cm. What is the area of a sector of the circle with angle 135°, leaving the answer in terms of x and π?

A.

\( \frac{\pi x^2}{8} \)

B.

\( \frac{3\pi x^2}{8} \)

C.

\( \frac{5\pi x^2}{8} \)

D.

\( \frac{3\pi x}{8} \)

Correct answer is B

A = θ 360 x πr2 = 135 360 x π x x2 = (3πx2)/8

20,125.

An atom radiates 1.5 x \(10^{-19}\)J of energy when an electron jumps from one energy level to another. What is the wavelength of the emitted radiation? (Planck’s constant =6.6 x \(10^{-34}\)Js. Speed of light in air=3 x \(10^{8}ms^{-1}\)

A.

1.32 x \(10^{-6}\)m

B.

2.98 x \(10^{-6}\)m

C.

3.32 x \(10^{-6}\)m

D.

6.82 x \(10^{-6}\)m

E.

8.01 x \(10^{-6}\)m

Correct answer is A

\(E=\lambda v=\frac{hc}{\lambda}\Rightarrow\lambda=\frac{hc}{E}={6.6 \times10^{-34}\times3\times10^8}{1.5\times10^{-19}}\\=1.32\times10^{-6}\)