10 questions from the JAMB 2011 Physics paper, with answers and explanations. Tap "Show answer" under each one when you are ready.
JAMB 2011Question 1 · Electricity and Magnetism
Three similar cells each of e.m.f 2 v and internal resistance 2Ω are connected in parallel, the total e.m.f and total internal resistance are respectively
A.6 v, 6.0Ω
B.2 v, 0.7Ω
C.2 v, 6.0Ω
D.6 v, 0.7Ω
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Answer: B. 2 v, 0.7Ω
Cells in parallel: total emf=2V (same as one cell); total internal resistance=32≈0.7 ohms.
JAMB 2011Question 2 · Electricity and Magnetism
If the charge of electricity is K wh is N4, what is the cost of operating an electrical appliance rated 250 v,2A for six hours?
A.N28
B.N12
C.N16
D.N24
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Answer: B. N12
Energy=250Vx2Ax6h=3000Wh=3kWh; cost=3x4=N12.
JAMB 2011Question 3 · Electricity and Magnetism
The correct expression for the potential at a point distance r from a charge q in an electric field is?
A.4πεor2q2
B.4πεorq2
C.4πεor2q
D.4πεorq
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Answer: D.4πεorq
Electric potential V=q/(4πε0r).
JAMB 2011Question 4 · Electronics and Alternating Current
The electrical properties of germanium can be altered drastically by the addition of impurity. This process is referred to as
A.saturation
B.bonding
C.amplification
D.dopping
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Answer: D. dopping
Adding controlled impurity to a semiconductor is called doping.
JAMB 2011Question 5 · Heat and Thermodynamics
The ground is always cold at night because the
A.atmosphere absorbs the sun's energy at night
B.earth radiates heat to the atmosphere at night
C.sun no longer shine at night
D.atmosphere reflects the sun's energy at night
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Answer: B. earth radiates heat to the atmosphere at night
At night, the earth radiates heat to the atmosphere, cooling the ground.
JAMB 2011Question 6 · Heat and Thermodynamics
If the volume of a gas increases steadily as the temperature decreases at constant pressure, the gas obeys
A.Graham's Law
B.Boyle's Law
C.Pressure law
D.Charles Law E. No Correct Option
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Answer: D. Charles Law E. No Correct Option
At constant pressure, volume increasing as temperature decreases follows Charles' Law.
JAMB 2011Question 7 · Mechanics, Motion, and Energy
A machine is used to lift a load of 20N through a height of 10m. if the efficiency of the machine is 40%, how much work is done?
A.80J
B.500J
C.300J
D.120J
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Answer: B.500J
Output work=20x10=200J; at 40% efficiency, input work=0.4200=500J.
JAMB 2011Question 8 · Nuclear and Modern Physics
A radioactive isotope has a decay constant of 10-5s4. Calculate half life
A.6.93×10−5s
B.6.93×105s
C.6.93×104s
D.6.93×10−4s
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Answer: C.6.93×104s
t½=0.693/λ=0.693/1×10−5=6.93×104 s.
JAMB 2011Question 9 · Properties of Matter and Fluids
I. Density of the liquid. II. Depth below the surface of the liquid. III. Surface area of the liquid. In which of the statement above will pressure be dependent?
A.I and II only.
B.II and III only.
C.I, II and III only.
D.I and III only.
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Answer: A. I and II only.
Liquid pressure depends on density and depth, not surface area.
JAMB 2011Question 10 · Waves, Sound, and Optics
A cannon is fired from town X,after how long is the sound heard at a town Y 4.95km away? [velocity of sound in the air = 330ms−1]
A.30s
B.10s
C.10s
D.15s
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Answer: D.15s
t=distance/speed=3304950=15s.
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