1992 - JAMB Physics Past Questions and Answers - page 4

31
If a plastic sphere floats in water (density = 1000kgm3) with 0.5 of its volume submerged, and floats in oil with 0.4 of its volume submerged the density of the oil is
A
800kgm3
B
1200kgm3
C
1250kgm3
D
2000kgm3
correct option: a

R.d = (\frac{0.4}{0.5}) = 0.8

0.8 = (\frac{\text {Density of oil}}{\text{Density of water}})

0.8 = (\frac{\text {Density of oil}}{1000})

Density of oil = 800kgm3

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32
A platinum resistance thermometer wire has a resistance of 5 ohms at 0oC and 5.5 ohms at 100oC. Calculate the temperature of the wire when the resistance is 5.2 ohms
A
80oC
B
60oC
C
40oC
D
10oC
correct option: c

100oC .... 5.5

(\theta)oC .... 5.3

0oC .... 5.0

(\frac{\theta - 0}{100 - 0}) = (\frac{5.5 - 5 .0}{5.5 - 5.0})

(\theta) = 40oC

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33
A bridge made of steel is 600m long. What is the daily variation in its length if the night-time and daytime temperatures are 10oC and 35oC respectively. The linear expansivity of steel is 0.000012C-1
A
0.18cm
B
1.80cm
C
18.00cm
D
1800cm
correct option: a

(\alpha) = (\frac{extension}{L\Delta\theta})

0.000012 = (\frac{e}{600 \times (35 - 10})

= 0.18cm

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34
One of the most important applications of bi-metallic strip is found in the construction of
A
a thermostat
B
an altimeter
C
a thermocouple
D
a hydrometer
correct option: a
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35
At constant pressure, the density of a fixed mass of gas is
A
constant with temperature
B
proportional to its volume
C
inversely proportional to its temperature
D
independent of its volume
correct option: c
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36
How much heat is absorbed when a block of copper of mass 0.05kg and specific heat capacity 390Jkg-1K-1 is heated from 20oC to 70oC?
A
39 . 98 x 10-1J
B
9.75 x 102J
C
3.98 x 103J
D
9.75 x 103J
correct option: b

Q = mc(\theta)

= 0.05 x 390 x (70 - 20)

= 975J

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37
A block of ice floats on water inside a container. If the block of ice gets completely melted, the level of water in the container will
A
increase
B
remain the same
C
decrease
D
first decrease and then increase
correct option: b
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38
The space between the double glass walls of a thermos flask is evacuated space are silvered. The residual source of heat loss takes place by
A
convection
B
radiation from the surface
C
conduction through the stopper and the glass
D
conduction across the walls
correct option: c
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39
The equation of a wave is y = 0.005 sin[x(0.5X - 200t)] where x and y are in meters and t is in seconds. What is the velocity of the wave?
A
4000ms-1
B
400ms-1
C
250ms-1
D
40ms-1
correct option: b

y = 0.005 sin[x(0.5X - 200t)]

compare to Y = A sin(kx - wt)

(\lambda) = (\frac{2\pi}{k}) and F = (\frac{w}{2\pi})

V= (\lambda)F

= (\frac{2\pi}{0.5}) x (\frac{200}{2\pi})

= 400ms-1

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40
Which of the following characteristics of a wave is used in the measurement of the depth of the sea?
A
diffraction
B
interference
C
refraction
D
reflection
correct option: d
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