WAEC Physics Past Questions & Answers - Page 84

416.

At which position should an object be placed in front of a concave mirror in order to obtain an image which is of the same size as the object?

A.

at the centre of curvature

B.

at the principal focus

C.

between the pole and principal focus

D.

between the centre of curvature and principal focus

Correct answer is A

No explanation has been provided for this answer.

417.

The equation of a certain progressive transverse wave is y = 2 sin 2 \(\pi ( \frac{t}{0.01} - \frac{x}{30})\), where x and y are in cm and t in seconds. Calculate the period of the wave.

A.

0.001s

B.

0.010s

C.

10.000s

D.

100.000s

Correct answer is B

Compare: Y = 2 sin 2 \(\pi (\frac{t}{0.01} - \frac{x}{30})\)

with the wave equation,

y = A sin 2 \(\pi (\frac{t}{T} - \frac{x}{\lambda}\))

⇒ \(\frac{t}{T} = \frac{t}{0.01}\)

T = 0.010s

418.

When salt is dissolved in water, the freezing point of the water

A.

increases

B.

decreases

C.

remains the same

D.

increases and later decrease

Correct answer is B

The salt in the water (same for any other impurities) lowers the freezing point of the solution so that water freezes at a lower temperature.