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WAEC Physics Past Questions & Answers - Page 160

796.

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

thermal capacity

has lower specific heat capacity

latent heat of fusion

latent heat of vaporisation

View answer & explanation

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]

0.119^oC

0.840^oC

1.190^oC

8.400^oC

View answer & explanation

Correct answer is A

mgh = mc $\theta$

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

= 0.119^oC

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 2.5^oC per second, calculate the specific heat capacity of the liquid. [Assume no heat is lost]

1100Jkg^-1K^-1

320Jkg^-1K^-1

200Jkg^-1K^-1

176Jkg^-1K^-1

View answer & explanation

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?

ms $\theta$ = mv^-1

ms = C

ms = s $\theta$

ms = c $\theta$

View answer & explanation

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

10.0^oC

15.0^oC

20.0^oC

30.0^oC

View answer & explanation

Correct answer is A

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

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

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

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