WAEC Physics Past Questions & Answers - Page 131

651.

It takes a shorter time for a liquid to boil at the top of a mountain than at the base because at the top, the

A.

temperature is higher

B.

pressure is lower

C.

humidity is higher

D.

temperature is constant

Correct answer is B

No explanation has been provided for this answer.

652.

The working principle of a pressure cooker is based on the

A.

increase in the volume of steam inside it

B.

complete trapping of heat inside it

C.

increase in the pressure of the pot

D.

decrease in the pressure of the pot

Correct answer is C

No explanation has been provided for this answer.

653.

Water of mass 1.5kg is heated from from 30oC to 80oC using an electric kettle which is rated 5A, 230V. Calculate the time taken to reach the final destination [specific heat capacity of water 4200Jkg-1K-1]

A.

4.57 minutes

B.

5.02 minutes

C.

7.30 minutes

D.

10.04 minutes

Correct answer is A

t = \(\frac{MC\theta}{2} = \frac{1.5 \times 4200 \times 50}{5 \times 230}\)

= 273.91s or 4.57 mins

655.

A metal rod of length 50cm is heated from 40oC to 80oC. If the linear expansivity of the material is \(\alpha\), calculate the increase in length of the rod (in metres) in terms of \(\alpha\)

A.

20\(\alpha\)

B.

200\(\alpha\)

C.

2000\(\alpha\)

D.

20000\(\alpha\)

Correct answer is A

\(L_2 - L_1 = \alpha_1 (\theta_2 - \theta_1) = \alpha \times 0.5 \times 40 = 20 \alpha\)