WAEC Physics Past Questions & Answers - Page 94

466.

The thermopile is a device for detecting

A.

radioactive radiations

B.

radiant energy

C.

x-rays

D.

the presence of electrons

Correct answer is B

No explanation has been provided for this answer.

467.

A metal sheet of area 100cm\(^2\) was heated through 70°C. Calculate its new area if the linear expansivity of the metal is 0.000017K\(^{-1}\).

A.

100.06 cm2

B.

100.12cm2

C.

100.24cm2

D.

100.36cm2

Correct answer is C

Formula: A\(_2\) = A\(_1\)(1 + \(\beta \theta\))

where \(\beta\) = The area expansivity

\(\theta\) = Change in temperature.

\(\beta\) = 2\(\alpha\)

where \(\alpha\) = linear expansivity of the body.

⇒ \(\beta\) = 2 x 0.000017 

= 0.000034 K\(^{-1}\)

\(\therefore\) A\(_2\) = 100 (1 + (0.000034 x 70))

= 100(1 + 0.00238)

= 100(1.00238)

= 100.238 cm\(^2\)

= 100.24 cm\(^2\) (to 2 d.p)

468.

A body is pulled through a distance of 500m by a force of 20N. If the power developed is 0.4kW, calculate the time for which the force acts

A.

250.0s

B.

25.0s

C.

2.5s

D.

0.5s

Correct answer is B

Force x Distance = Power x Time

Time = \(\frac{Force \times Distance}{Power}\)

= \(\frac{20 \times 500}{0.4 \times 1000}\)

= 25.0s

469.

The S.I unit of heat is

A.

joule

B.

kelvin

C.

watt

D.

ampere

Correct answer is A

Heat is a form of energy (heat energy). The S.I unit of energy generally is Joules (J).

470.

A girl stands on a scale in a lift. If the reading on the scale is less than her weight, then the lift is moving

A.

upward at uniform speed

B.

upward with uniform acceleration

C.

downward with uniform speed

D.

downward with uniform acceleration

Correct answer is D

No explanation has been provided for this answer.