2004 - JAMB Physics Past Questions and Answers - page 3

21
The pitch of a sound note depends on
A
timbre
B
frequency
C
harmonics
D
quality
correct option: b
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22
If u is the object distance and v the image distance, which of the following expressions gives the linear magnification produced by a convex lens of focal length f?
A
u/f - f
B
u/v + f
C
v/f + 1
D
v/f - 1
correct option: d

Magnification, M = v/u = v (1/u)

And for the Lens formula 1/u + 1/v = 1/f

=> 1/u = 1/f - 1/v

∴M = V(1/u)

= V(1/f - 1/v) = v/f - v/v = v/f - 1

∴M = v/f - 1

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23
The refractive index of the medium M in the diagram above is
A
1/√3
B
2√3
C
√3
D
2/√3
correct option: c

From the above diagram ; ? = 90o - 30o = 60o

v = 90 - 60 = 30

∴ refractive index = (sin ?)/(sin v) = (sin 60o / sin 30o) = √3/2/1/2

= √3/2 x 1/2

= √3

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24
When left in a freezer, a bottle full of water cracks on freezing into ice because of the
A
increase in the volume of water
B
contraction of the bottle
C
expansion of the bottle
D
decrease in the volume of water
correct option: a
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25
The phase difference between waves P and q in the diagram above is
A
B
π
C
π/4
D
π/2
correct option: d
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26
The change in volume when 450kg of ice is completely melted is
[density of ice = 900 kgm-3, density of water = 100 kgm-3]
A
0.50m3
B
0.45m3
C
0.05m3
D
4.50m3
correct option: c

Vol. of ice = M/?D = 450/900 = 0.500m3

vol. of water = M/D" = 450/1000 = 0.450m3

∴ Difference in vol. = 0.500 - 0.450

= 0.05m3

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27
Tea pots are often silver-coated to prevent heat loss by
A
conduction only
B
convention only
C
convection and conduction
D
radiation only
correct option: d
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28
I. Wavelength
II. Medium of propagation
III. Wave velocity
IV. Frequency
V. Energy

Which of the above are used for characterizing waves?
A
I, II and V
B
I and IV
C
I, III and IV
D
III, IV and V
correct option: c
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29
A 50W electric heater is used to heat a metal block of mass 5kg. If in 10 minutes a temperature rise of 12oC is achieved, the specific heat capacity of the metal is
A
400 J kg-1K-1
B
500 J kg-1K-1
C
390 J kg-1K-1
D
130 J kg-1K-1
correct option: b

Heat supplied by the heater in 10 mins

= power x time

= 50 x (10 x 60)

= 30000 J

This heat is equal = MCΔt

= 5 x c x 12

= 60cJ

= 60C = 30,000

C = 30,000/60

C = 500 J kg-1K-1

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30
Metal rods of length 20m each are laid end to end to form a bridge at 25oC. What gap will be provided between consecutive rails for the bridge to withstand 75oC?
[Linear expansivity of the material = 2.0 x 10-5K-1
A
0.20m
B
0.22m
C
0.25m
D
0.02m
correct option: d

Safety gap = expansion of the rod

= ∝Lo Δ t

= 2.0 x 10-5 x 20 x (75 - 25)

= 2.0 x 10-5 x 20 x 50

= 2.0 x 10-5 x 103

= 2.0 x 10-2 OR 0.02m

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