10 questions from the JAMB 2012 Physics paper, with answers and explanations. Tap "Show answer" under each one when you are ready.
JAMB 2012Question 1 · Electricity and Magnetism
A newly charged 12V accumulator can easily start a car whereas eight new dry cells in series with a effective e.m.f. of 12V cannot start the same car because
A.The current capacity is high
B.The current capacity is low
C.it cannot be re-charged
D.it cannot easily be connected to a car
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Answer: A. The current capacity is high
An accumulator has a much higher current capacity (lower internal resistance) than dry cells.
JAMB 2012Question 2 · Electronics and Alternating Current
The current output from of an a.c. source is given as I = 10 sin to t. The d.c equivalent of the current is
A.5.0A
B.7.1A
C.10.0A
D.14.1A
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Answer: B.7.1A
rms current=Ipeak/2=1.41410=7.1A.
JAMB 2012Question 3 · General Physics and Measurement
In order to remove the error of parallax when taking measurements with a metre rule, the eye should be focused
A.slantingly towards the right on the markings
B.slantingly towards the left on the markings
C.vertically downwards on the markings
D.vertically upwards on the markings
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Answer: C. vertically downwards on the markings
To avoid parallax error, the eye should look vertically down on the scale markings.
JAMB 2012Question 4 · Heat and Thermodynamics
Calculate the temperature change when 500J heats 100g of water. [Specific heat capacity of water =4200Jkg−1K−1]
A.12.1∘C
B.2.1∘C
C.1.2∘C
D.0.1∘C
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Answer: C.1.2∘C
ΔT=mcQ=(0.1)(4200)500≈1.2∘C.
JAMB 2012Question 5 · Mechanics, Motion, and Energy
Calculate the total distance covered by a train before coming to rest if its initial speed is 30ms−1 with a constant retardation of 0.1m−2
A.5500m
B.4500m
C.4200m
D.3000m
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Answer: B.4500m
0=900-2(0.1)s gives s=4500m.
JAMB 2012Question 6 · Mechanics, Motion, and Energy
An object of mass 20kg slides down an inclined plane at an angle of 30∘ to the horizontal. The coefficient of static friction is? [g = 10ms−2 ]
A.0.2
B.0.3
C.0.5
D.0.6
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Answer: D. 0.6
At the point of sliding, tan(theta)=coefficient of friction: tan30=0.577≈0.6.
JAMB 2012Question 7 · Nuclear and Modern Physics
A piece of radioactive material contains 1000 atmos. If its half -life is 20seconds, the time taken for 125 atoms to remain is
A.20 seconds
B.40 seconds
C.80 seconds
D.60 seconds
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Answer: D. 60 seconds
1000125=81=(1/2)3, so t=3 half-lives=60s.
JAMB 2012Question 8 · Properties of Matter and Fluids
A balloon whose volume is 300m3 is filled with hydrogen. If the density of air is 1.3kgm−3 , find the upthrust on the balloon. [g = 10ms−2 ]
A.3000N
B.3800N
C.3900N
D.4200N
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Answer: C.3900N
Upthrust=weight of air displaced=1.3x300x10=3900N.
JAMB 2012Question 9 · Waves, Sound, and Optics
The characteristic of a vibration that determines its intensity is the
A.Frequency
B.Overtone
C.Wavelength
D.Amplitude
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Answer: D. Amplitude
Amplitude determines the intensity of a vibration.
JAMB 2012Question 10 · Waves, Sound, and Optics
After reflection from the concave mirror, rays of light from the sun converges
A.at the radius of curvature
B.at the focus
C.beyond the radius of curvature
D.between the focus and radius of curvature
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Answer: B. at the focus
Parallel rays from the sun converge at the focus after reflecting off a concave mirror.
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