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JAMB Physics Past Questions & Answers - Page 24

116.

The velocities of light in air and glass are 3.0 x 108ms1 and 2.0 x 108ms1 respectively. If the angle of refraction is 30º, the sine of the angle of incidence is? 

A.

0.33

B.

0.50

C.

0.67

D.

0.75

Correct answer is D

sin isin r = velocity in airvelocity in glass

sin isin 30 = 3×1082×108

Sin i = 34 = 0.75

117.

The inside portion of part of a hollow metal sphere of diameter 20cm is polished. The portion will therefore form a?

A.

concave mirror of focal length 5cm

B.

concave mirror of focal length 10cm

C.

convex mirror of focal length 5cm

D.

convex mirror of focal length 10cm

Correct answer is C

Concave Mirror: It is a spherical mirror whose outer surface is polished and inner or concave side is reflecting surface.

Convex Mirror: It is a spherical mirror whose inner surface is polished and outer side or convex side is the reflecting surface.

f = m4 = f = d4

f = 204 = 5cm

118.

A man stands 4m in front of a plane mirror. If the mirror is moved 1m towards the man, the distance between him and his new image is?

A.

3m

B.

5m

C.

6m

D.

10m

Correct answer is C

Objects distance (u) = image distance (v)

object distance = 3m

|uv| = 3 + 3 = 6m

119.

The lowest note emitted by a stretched string has a frequency of 40Hz. How many overtones are there between 40Hz and 180Hz?

A.

4

B.

3

C.

2

D.

1

Correct answer is B

f0 = 40H3

1st overtone = 2f0 = 80H3

2nd overtone = 3f0 = 120H3

3rd overtone = 4f0 = 160H3

4th overtone = 5f0 = 200H3

Number of overtones between 40H_{3} and 180H_{3} = 3

120.

If a sound wave goes from a cold air region to a hot air region, its wavelength will?

A.

increase

B.

decrease

C.

decrease then increase

D.

remain constant

Correct answer is A

No explanation has been provided for this answer.