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WAEC Physics Past Questions & Answers - Page 11

51.

Which of the following statements-about electromagnetic waves is not correct?

A.

They carry energy as they travel through space

B.

They travel with the speed of light

C.

They are longitudinal

D.

The electric and magnetic fields are at right angles to each other

View answer & explanation

Correct answer is C

All electromagnetic waves are:

transverse waves; can travel through a vacuum ;
travel at exactly the same speed in a vacuum, the speed of light, 300,000,000 m/s.
transfer energy from one place to another;
can be reflected;
can be refracted .
The oscillations of and are perpendicular to each other and are in the same phase.

52.

The distance between the fixed points of a mercury-in-glass thermometer is 30 cm. Determine the temperature when the mercury level is 10.5 cm above the lower fixed point

A.

28.6ºC

B.

30.0 ºC

C.

35.0 ºC

D.

40.5 ºC

View answer & explanation

Correct answer is C

$\frac{10.5-0}{30-0}$ = $\frac{c-0}{100-0}$

$\frac{10.5}{30}$ = $\frac{c}{100}$

cross multiply:

10.5 * 100 = 30c

35.0 ºC = c

53.

A hunter fires a gun at a point 408 m away from a cliff. If he hears an echo 2.4 s later, determine the speed of the sound wave

A.

340 ms $^{-1}$

B.

380 m s $^{-1}$

C.

400 m s $^{-1}$

D.

680 m s $^{-1}$

View answer & explanation

Correct answer is A

speed of the sound wave = $\frac{distance * 2}{time}$

= $\frac{408 * 2}{2.4}$

: speed of the sound wave = 340 ms $^{-1}$

54.

When the direction of vibration of the particles of a medium is perpendicular to the direction of propagation of a wave, the wave is said to be--------

A.

longitudinal

B.

transverse

C.

mechanical

D.

a sound wave

View answer & explanation

Correct answer is B

In physics, a transverse wave is a wave whose oscillations are perpendicular to the direction of the wave's advance.

This is in contrast to a longitudinal wave which travels in the direction of its oscillations. Water waves are an example of transverse wave.

55.

The half-life of a radioactive substance is 15 hours. If at some instance, the sample has a mass of 512 g, calculate the time it will take $\frac{7}{8}$ of the sample to decay

A.

15 hours

B.

30 hours

C.

45 hours

D.

60 hours

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

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