JAMB Physics 2020 past questions

Checked by the Skolra question team · Last updated 23 October 2026

Ten questions from the 2020 JAMB Physics paper, with answers and explanations. We hold 38 questions from this paper, and the Skolra app has all of them.

JAMB Physics 2020 questions and answers

1.
Heat is supplied uniformly at the rate of 100W to 1.0 x 10 $^{-2}$ kg of a liquid for 20 seconds. If the temperature of the liquid rises by 5 $^o$ C, then the specific heat capacity of the liquid is
1. A
  2.0 x 10^5 J/kg°C
2. B
  4.0 x 10^3 J/kg°C
3. C
  4.0 x 10^4 J/kg°C
  Correct
4. D
  2.0 x 10^4 J/kg°C
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Answer: C
Step 1: Find the heat supplied using Q = Pt = 100W x 20s = 2000 J.
Step 2: Use the specific heat capacity formula Q = mcΔθ, so c = Q/(mΔθ).
c = 2000 / (1.0 x 10^-2 x 5) = 2000 / 0.05 = 4.0 x 10⁴ J/kg°C.
The answer of 4.0 x 10⁴ J/kg°C is correct.
The value 2.0 x 10⁵ J/kg°C comes from dividing the heat by the mass alone and forgetting to also divide by the temperature rise. The value 4.0 x 10³ J/kg°C is a decimal-place slip, misplacing the power of ten in the mass. The value 2.0 x 10⁴ J/kg°C results from using half the correct heat supplied, as if the time were only 10 seconds instead of 20.
2.
A hydrometer is an instrument for measuring the
1. A
  viscosity of a liquid
2. B
  atmospheric pressure
3. C
  relative density of a liquid
  Correct
4. D
  surface tension of a liquid
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Answer: C
A hydrometer is an instrument that floats in a liquid and measures the relative density (specific gravity) of that liquid, by reading off how deep the calibrated stem sinks. It works on the principle of flotation: a denser liquid supports more of the stem out of the liquid, and the scale is marked accordingly.
Viscosity (a liquid's resistance to flow) is measured with a viscometer, not a hydrometer, so that option confuses two different fluid properties. Surface tension is measured with instruments such as a stalagmometer or tensiometer. Atmospheric pressure is measured with a barometer, which is a completely different instrument used for a different physical quantity altogether.
3.
Which of the following statements about radioactivity is true?
(i) Alpha particle is positively charged
(ii)Beta particle is negativelycharged
(iii) Gamma ray is neutral
(iv) Beta particle has thesame massas helium atom
(v) Gamma ray is charged.
1. A
  (ii), (iii) and (v) only
2. B
  (i), (iv) and (v) only
3. C
  (i), (ii) and (iv) only
4. D
  (i), (ii) and (iii) only
  Correct
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Answer: D
Check each statement:
(i) An alpha particle is a helium nucleus, so it is positively charged — true.
(ii) A beta particle is a fast-moving electron, so it is negatively charged — true.
(iii) A gamma ray is electromagnetic radiation with no mass and no charge, so it is neutral — true.
(iv) A beta particle (an electron) has a mass far smaller than a helium atom (an alpha particle is about 7000 times heavier than a beta particle) — this statement is false, and mixing up beta with alpha mass is a common slip.
Therefore the true statements are those saying the alpha particle is positively charged, the beta particle is negatively charged, and the gamma ray is neutral.
4.
The lower and upper fixed points marked on a Mercury-in-glass thermometer are 210mm apart. The end of the mercury column in the tube is 49mmabove the lower fixed point in a room. What is the temperature of the room in degrees Celsius?
1. A
  23.3°C
  Correct
2. B
  76.7°C
3. C
  20.5°C
4. D
  46.6°C
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Answer: A
23.3°C is correct.
On a mercury-in-glass thermometer, the lower fixed point (0°C, the ice point) and the upper fixed point (100°C, the steam point) are calibrated so that the whole 210 mm gap represents a 100°C rise.
Using the formula:
θ = (length above lower fixed point ÷ total fundamental interval) × 100
θ = (49 ÷ 210) × 100 = 23.3°C
The distractor 76.7°C comes from measuring from the wrong end (using 210 − 49 = 161 mm instead of 49 mm). The other two values come from simple arithmetic slips in the same formula, such as doubling the mercury length or dividing by the wrong total.
5.
When a sound wave passes from air into water its
1. A
  speed decreases but its frequency remains unchanged
2. B
  speed increases but its wavelength remains unchanged
3. C
  frequency remains unchanged but its wavelength increases
  Correct
4. D
  wavelength decreases while its frequency increases
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Answer: C
Frequency stays the same; wavelength increases.
The frequency of a wave is fixed by whatever is generating it (the source), not by the medium it travels through. So as sound crosses from air into water, the frequency remains unchanged.
What does change is the speed. Sound actually travels faster in water than in air, because water is a much stiffer (less compressible) medium relative to its density, and this raises the wave speed even though water is denser.
Using v = fλ: since frequency (f) is constant and speed (v) increases on entering water, the wavelength (λ) must increase to match.
6.
If in a simple pendulum experiment the length of the inextensible string is increased by a factor offour, its period is increased by a factor of?
1. A
  8
2. B
  2
  Correct
3. C
  4
4. D
  16
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Answer: B
The period of a simple pendulum is given by T = 2π√(L/g), which shows that T is proportional to the square root of the length, not to the length itself.
If the length is increased by a factor of four (L becomes 4L), the new period becomes 2π√(4L/g) = 2 × 2π√(L/g), which is 2 times the original period.
A candidate who forgets the square root and assumes T is directly proportional to L would wrongly pick 4. Squaring the factor instead of taking its root gives 16, and doubling the wrong way gives 8 — both are errors from misapplying the length-period relationship.
7.
The force required to make an object of mass m, travelling with velocity v, turn in a circle of radius r is
1. A
  mv²/r
  Correct
2. B
  mv²r
3. C
  mv/r
4. D
  mvr²
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Answer: A
An object moving in a circle of radius r with speed v has a centripetal acceleration directed towards the centre, given by a = v²/r.
By Newton's second law, the force needed to produce this acceleration is F = ma, so the centripetal force is F = mv²/r.
The expression mv/r looks similar but leaves out that the velocity term must be squared, since acceleration in circular motion depends on v², not v.
The expressions mvr² and mv²r wrongly put r in the numerator instead of the denominator — remember that a smaller radius (a tighter turn) requires a larger force, so r must divide the expression, not multiply it.
8.
A solid weighs 4.8g in air, 2.8g in water and 3.2g in Kerosine. The ratio of density of the solid to that of the kerosine is
1. A
  1.5 : 1
2. B
  2 : 1
3. C
  3 : 1
  Correct
4. D
  4 : 3
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Answer: C
Step 1: Find the relative density of the solid (using water).
Loss of weight in water = 4.8g − 2.8g = 2.0g. This loss equals the weight of water displaced, which is proportional to the solid's volume.
Relative density of solid = weight in air ÷ loss of weight in water = 4.8 ÷ 2.0 = 2.4 (relative to water).
Step 2: Find the relative density of the kerosine (also relative to water).
Loss of weight in kerosine = 4.8g − 3.2g = 1.6g. Since the same solid (same volume) displaces both liquids, the ratio of the two losses equals the ratio of the two liquids' densities.
Density of kerosine (relative to water) = 1.6 ÷ 2.0 = 0.8.
9.
Which of the following pairs ispart of the electromagnetic spectrum?
I. Radio waves
II. sound waves
III. Gamma rays
IV. water waves
1. A
  III and IV only
2. B
  II and IV only
3. C
  I and III only
  Correct
4. D
  I and II only
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Answer: C
Radio waves and Gamma rays are correct. The electromagnetic spectrum is the family of waves produced by vibrating electric and magnetic fields together. These waves do not need any material medium and all travel at the speed of light in a vacuum. The full spectrum, from lowest to highest frequency, runs: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
10.
What is the cost of running five 50W lamps and four 100W lamps for 10 hours if electrical energy costs 2 Kobo per KWh?
1. A
  6.5 Kobo
2. B
  65 Kobo
3. C
  13 Kobo
  Correct
4. D
  130 Kobo
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Answer: C
Step 1: Find the total power.
Five 50W lamps = 5 × 50W = 250W.
Four 100W lamps = 4 × 100W = 400W.
Total power = 250W + 400W = 650W = 0.65kW.
Step 2: Find the energy consumed.
Energy = Power × time = 0.65kW × 10h = 6.5kWh.
Step 3: Find the cost.
Cost = 6.5kWh × 2 Kobo/kWh = 13 Kobo.
A candidate who forgets to convert watts to kilowatts before multiplying by the cost per kWh ends up with 650 × 2 = 1300, and mis-scaling that gives the wrong values of 65 Kobo or 130 Kobo. Another common slip is halving the correct energy value, giving 6.5 Kobo instead of the correct 13 Kobo.

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JAMB Physics 2020 past questions

JAMB Physics 2020 questions and answers

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