WAEC Physics Past Questions & Answers - Page 160

796.

The energy required to change a solid to liquid at constant temperature is called

A.

thermal capacity

B.

has lower specific heat capacity

C.

latent heat of fusion

D.

latent heat of vaporisation

Correct answer is C

No explanation has been provided for this answer.

797.

Water falls through a height of 50m. Determine the temperature rise at the bottom of the fall. [Neglect energy losses. Specific heat capacity of water = 4200Jkg-1 K-1, g = 10ms2]

A.

0.119oC

B.

0.840oC

C.

1.190oC

D.

8.400oC

Correct answer is A

mgh = mc\(\theta\)

\(\theta = \frac{gh}{c} = \frac{10 \times 50}{4200}\)

= 0.119oC

798.

An immersion heater rated 400W, 220V is used to heat a liquid of mass 0.5kg. If the temperature of the liquid increases uniformly at the rate of 2.5oC per second, calculate the specific heat capacity of the liquid. [Assume no heat is lost]

A.

1100Jkg-1K-1

B.

320Jkg-1K-1

C.

200Jkg-1K-1

D.

176Jkg-1K-1

Correct answer is B

pt = mc\(\theta\)

C = \(\frac{pt}{m \theta}\)

= \(\frac{400 \times 1}{0.5 \times 2.5}\)

= 320Jkg-1K-1

799.

A body of mass m, has a specific heat capacity s, and a heat capacity c. If the temperature of the body changes by \(\theta^oC\), Which of the following equation is correct?

A.

ms\(\theta\) = mv-1

B.

ms = C

C.

ms = s\(\theta\)

D.

ms = c\(\theta\)

Correct answer is B

Q = ms\(\theta\) = c \(\theta\)

ms = C

800.

The lower and upper fixed point of a thermometer are 30mm and 180mm respectively. Calculate the temperature in degrees Celsius when the thermometer reads 45mm

A.

10.0oC

B.

15.0oC

C.

20.0oC

D.

30.0oC

Correct answer is A

100....180
A......45
0......30

\(\frac{45 - 30}{180 - 30} = \frac{A - 0}{100 - 0}\)

A = \(\frac{15 \times 100}{150} = 10^oC\)