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WAEC Physics Past Questions & Answers - Page 42

206.

A rectangular piece of iron measuring 4 cm by 3 cm at 20oC is heated until its temperature increases by 100 C. Calculate the new area of the metal. [Linear expansivity of iron is 1.2x 105 K1]

A.

12.0144 cm3

B.

12.0346 cm3

C.

12.0288 cm3

D.

12.0173 cm3

Correct answer is C

Linear expansivity (α

= A2A1A1θ

Original Area(A1) = 4 x 3 = 12

New Area (A2) = ? 

Temp. rise (θ) = 100o

A2 - 12 = 1200 x 2 x 1.2 x 105 

A2 - 12 = 2880 x 105

A2 - 12 = 0.0288

A2 = 12.0288 cm2  

207.

A ray of light traveling from a rectangular glass block of refractive index 1.5 into air strikes the block at an angle of incidence of 30. Calculate its angle of refraction.

A.

48.6°

B.

19.5°

C.

20.0

D.

45.0

Correct answer is A

Given that refractive index = 1.5, angle of incidence = 30°, angle of refraction =?

using snell's law = refractive index = sinisinr

=1n=sin30sinr

= sinr=1.5×sin30

r =  sin10.75

= 48.6° 

this is because ray is traveling from a more denser medium to a less dense medium

208.

The anomalous expansion of water occurs in the range 

A.

0 °C to 100 °C

B.

0 °C to 4 °C

C.

4 °C to 100 C

D.

-4 °C to 0 °C

Correct answer is B

No explanation has been provided for this answer.

209.

Which property of a wave remains constant when the wave travels from one medium into another?
 

A.

Amplitude

B.

Wavelength

C.

Velocity

D.

Frequency

Correct answer is D

Frequency remains unchanged as waves travel from one medium to another because it is characterized by the source of the wave.

210.

A device consumes 100 W of power when connected to a 120 V source. Calculate its resistance

A.

1.2Ω

B.

12,000 Ω

C.

20.0Ω

D.

144Ω

Correct answer is D

P = V2R 

R = 1202100

= 144.0Ω