WAEC Physics 1990 past questions

Checked by the Skolra question team · Last updated 15 October 2026

Ten questions from the 1990 WAEC Physics paper, with answers and explanations. We hold 45 questions from this paper, and the Skolra app has all of them.

WAEC Physics 1990 questions and answers

1.When the direction of vibration of the particles of a medium is perpendicular to the direction of travel of a wave the wave transmitted is known as
1. A
  a stationary wave
2. B
  a longitudinal wave
3. C
  a progressive wave
4. D
  a transverse wave
  Correct
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Answer: D
Waves are classified by the relationship between the direction of particle vibration and the direction of wave propagation:
Transverse wave: particle vibration is perpendicular to the direction of wave travel (e.g. light, water surface waves).
Longitudinal wave: particle vibration is parallel to the direction of wave travel (e.g. sound).
Since the particles vibrate perpendicular to the direction of travel, the wave is a transverse wave.
2.If the temperature of water is gradually increased from 0° to 4°C, the density of the water within this range
1. A
  remains constant throughout
2. B
  decreases uniformly
3. C
  increases to a maximum at 4°C then decreases
  Correct
4. D
  decreases to a minimum at 0°C then increases
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Answer: C
Water exhibits an anomalous expansion behaviour between 0°C and 4°C. Unlike most substances, water contracts (becomes denser) as it is warmed from 0°C up to 4°C.
At 4°C, water reaches its maximum density of 1000 kg/m³ (1 g/cm³). Above 4°C, water expands normally as temperature rises and density decreases.
This anomalous behaviour is due to the breaking of hydrogen-bond structures (ice-like clusters) as temperature rises from 0°C, which causes the molecules to pack more closely together until 4°C, after which normal thermal expansion dominates.
3.What is the difference between a crystalline and an amorphous solid? A crystalline solid
1. A
  does not conduct electricity while an amorphous solid is a good conductor
2. B
  is always harder and denser than an amorphous solid of the same composition
3. C
  has a random arrangement of atoms while an amorphous solid has a regular lattice structure
4. D
  has a definite melting point while an amorphous solid softens gradually over a range of temperatures
  Correct
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Answer: D
The fundamental difference between crystalline and amorphous solids lies in their internal structure:
A crystalline solid has atoms, ions, or molecules arranged in a regular, repeating three-dimensional lattice pattern. This regular structure means all the bonds in a given direction break at the same temperature, giving the material a sharp, definite melting point.
An amorphous solid (e.g. glass, rubber) has a random, disordered internal arrangement similar to a frozen liquid. Its bonds break over a range of temperatures, so it softens gradually rather than melting sharply.
4.A particle of mass 2.5 x 10^-6kg revolving around the earth has a radial acceleration of 4 X 10⁷ ms^-2. What is the centripetal force of the particles?
1. A
  100 N
  Correct
2. B
  10 N
3. C
  10 000 N
4. D
  1 000 N
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Answer: A
Centripetal force is calculated using Newton's second law: F = ma
F = 2.5 × 10⁻⁶ kg × 4 × 10⁷ m s⁻²
F = (2.5 × 4) × 10^{(−6 + 7)} = 10 × 10¹ = 100 N
5.Calculate the resistance of the filament of a lamp rated 240 V, 40 W
1. A
  1440 Ω
  Correct
2. B
  960 Ω
3. C
  2880 Ω
4. D
  720 Ω
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Answer: A
The resistance of the filament is calculated from the power rating using:
R = V² / P
Substituting V = 240 V and P = 40 W:
R = (240)² / 40 = 57,600 / 40 = 1440 Ω
6.A bat emits a sound wave at a speed of 1650.0ms^-1 and receives the echoes 0.15s later. Calculate the distance of the bat from the reflector
1. A
  61.875 m
2. B
  247.5 m
3. C
  123.75 m
  Correct
4. D
  495.0 m
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Answer: C
The sound travels to the reflector and back, covering twice the distance to the reflector in the echo time.
Distance = (speed × time) / 2
Distance = (1650.0 × 0.15) / 2 = 247.5 / 2 = 123.75 m
7.Heat transfer by convection in a liquid is due to the
1. A
  differences in the densities of different parts of the liquid
  Correct
2. B
  molecular vibrations transmitted through the liquid
3. C
  conduction of heat through the liquid molecules
4. D
  radiation emitted by the heated part of the liquid
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Answer: A
Convection in a liquid occurs because of differences in density caused by temperature differences. When part of the liquid is heated it expands, becomes less dense, and rises; the cooler, denser liquid sinks to replace it, setting up convection currents.
This bulk movement of the fluid is the mechanism of convection heat transfer, distinct from conduction (vibration) and radiation (electromagnetic waves).
8.How much heat is given out when a piece of iron of mass 50g and specific heat capacity 460 Jkg^-1k^-1 cools from 85^oC to 25^oC?
1. A
  1 380 J
  Correct
2. B
  690 J
3. C
  138 J
4. D
  2 760 J
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Answer: A
Using the formula for heat transfer:
Q = mcΔT
m = 50 g = 0.050 kg, c = 460 J kg⁻¹ K⁻¹, ΔT = 85 − 25 = 60°C
Q = 0.050 × 460 × 60 = 1 380 J
9.When the pressure of the gas in a discharge tube is gradually lowered. I. there is a violet glow in the tube II. the glow in the tube splits into bands which get further apart. III, the glow and the bands eventually disappear and there is a green fluorescence in the tube. IV. the tube breaks into pieces. Which of the following are correct?
1. A
  I, II and III only
  Correct
2. B
  I, II, III and IV
3. C
  II and III only
4. D
  I and II only
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Answer: A
As pressure in a discharge tube is gradually reduced, the following sequence of events occurs:
I. At moderately reduced pressure, a violet/pink glow fills the tube. ✓
II. As pressure decreases further, the glow splits into alternating bright and dark bands (Faraday dark space, positive column striations) that move further apart. ✓
III. At very low pressures, the banded glow disappears, and the glass wall of the tube shows a green fluorescence caused by cathode rays striking the glass. ✓
IV. The tube does not break into pieces — this is physically incorrect. ✗
Therefore, only statements I, II and III are correct.
10.What is the electric potential energy between two protons each of charge q and at a distance of r apart? (Permittivity of free space = ε_o)
1. A
  q² / (4πε₀r²)
2. B
  q² / (4πε₀r)
  Correct
3. C
  q / (4πε₀r)
4. D
  2q² / (4πε₀r)
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Answer: B
The electric potential energy between two point charges is given by Coulomb's law for energy:
U = kq₁q₂ / r = q₁q₂ / (4πε₀r)
Since both protons have charge q, we substitute q₁ = q₂ = q:
U = q² / (4πε₀r)
Note: the denominator contains r (not r²), which distinguishes it from the force formula F = q²/(4πε₀r²).

The questions come from past JAMB, WAEC and NECO papers. We use software to help write the answer options and explanations, and every answer is checked twice before it goes on the site. How we check

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WAEC Physics 1990 past questions

WAEC Physics 1990 questions and answers

Practise all 45 questions we hold from the 1990 paper, on a timed CBT screen

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