WAEC Physics Past Questions & Answers

221.

Which of the following characteristics of waves can a ripple tank be used to demonstrate?
I. Reflection
II. Refraction
III. Diffraction

I, II and Ill

ll and ll only

l and lII only

I and II only

View answer & explanation

Correct answer is A

ripple tank experiment can be used to demonstrate the following properties of waves:

Reflection
Refraction

Diffraction

222.

The wire of a platinum resistance thermometer has d resistance of 3.5 $\Omega$ at 0 °C and 10.52 $\Omega$ at 100°C. Calculate the temperature of the wire when its resistance is 7.5 $\Omega$ .

78 °C

25 $^o$ C

30 $^o$ C

57 $^o$ C

View answer & explanation

Correct answer is D

Using the formula

t = $\frac{R - R_0}{R_{(100)} - R_0} \times 100^oC$

t = $\frac{7.5 - 3.5}{10.5 - 2..5} \times 100^oC$

= $\frac{4}{7} \times 100$

= 57.14 $^o$ C

~ 57 $^o$ C

223.

Calculate the quantity of heat needed to change the temperature of 60g of ice at 0 °C to 80 °C. [specific latent heat of fusion of ice= 3.36 x 10 $^5$ Jkg $^{-1}$ specific heat capacity of water 4.2 x 10 $^3$ J kg $^{-1}$ K $^{-1}$ ]

4.80 kJ

20.16 kJ

40.32 kJ

22.17 kJ

View answer & explanation

Correct answer is C

Heat needed to change 60g (0.06kg) of ice at 0 $^o$ C to water at 0 $^o$

= 0.06 x 3.36 x 10 $^5$ J

= 0.2016 x 10 $^5$ J

Heat required to raise the temp. of 60g (0.06kg) of water from 0 $^o$ C to 80 $^o$ C

= 0.06 x 4.2 x 10 $^3$ x (80.0)J

= 0.06 x 4.2 x 10 $^3$ x 80

= 20.16 x 10 $^3$

= 0.2016 x 10 $^5$

Total heat needed = (0.2016 + 0.2016) 10 $^5$ J

= 0.4032 x 10 $^5$ J

= 40.32KJ

224.

A small amount of air is introduced into the vacuum above the mercury in a mercury barometer tube. The mercury level goes down because the air molecules

heat the mercury and make it expand

increase the pressure above the mercury.

cool the mercury and make it contract.

decrease the pressure above the mercury

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

225.

If the efficiency of a transformer is 100%, which of the following equations would be correct?

N $_p$ E $_p$ = N $_s$ E $_s$

N $_s$ I $_p$ = N $_p$ I $_s$

N $_s$ I $_s$ = N $_p$ I $_p$

I $_p$ E $_s$ = I $_s$ E $_p$

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

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