WAEC Physics 1993 past questions
Ten questions from the 1993 WAEC Physics paper, with answers and explanations. We hold 52 questions from this paper, and the Skolra app has all of them.
WAEC Physics 1993 questions and answers
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1.A solid metal cube of side 10 cm is heated from 10°C to 60°C. If the linear expansivity of the metal is 1.2 x 10⁻⁵K⁻¹, calculate the increase in its volume.
- A0.18 cm³
- B1.8 cm³Correct
- C0.6 cm³
- D3.6 cm³
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Answer: B
The cubical (volume) expansivity γ = 3α = 3 × 1.2 × 10⁻⁵ = 3.6 × 10⁻⁵ K⁻¹
Original volume: V₀ = (10 cm)³ = 1000 cm³
Temperature change: ΔT = 60 − 10 = 50 K
ΔV = V₀ × γ × ΔT = 1000 × 3.6 × 10⁻⁵ × 50 = 1.8 cm³
- A
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2.An object is projected with a velocity of 100 ms⁻¹ from the ground level at an angle θ to the vertical. If the total time of flight of the projectile is 10 s, calculate θ. (g = 10 ms⁻²).
- A45°
- B30°
- C75°
- D60°Correct
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Answer: D
The angle θ is measured from the vertical. The component of velocity along the vertical (upward) is u·cosθ.
Total time of flight: T = 2u cosθ / g
Substituting values:
10 = 2 × 100 × cosθ / 10
10 = 20 cosθ
cosθ = 0.5
θ = cos⁻¹(0.5) = 60°
- A
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3.How long does it take a 750 W heater operating at full rating to raise the temperature of 1 kg of water from 40°C to 70°C?
- A84 s
- B168 sCorrect
- C126 s
- D336 s
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Answer: B
Heat required: Q = mcΔT = 1 × 4200 × (70 − 40) = 1 × 4200 × 30 = 126,000 J
Time: t = Q/P = 126,000 / 750 = 168 s
- A
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4.Which of the following is not a conductor of electricity?
- AMercury
- BGlassCorrect
- CGraphite
- DCopper
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Answer: B
Glass is an insulator, not a conductor of electricity. Its electrons are tightly bound and not free to move.
Copper, graphite, and mercury are all electrical conductors — they possess free charge carriers (electrons or ions) that can move under a potential difference.
- A
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5.Which of the following are correct of plane-polarized light? I. Plane polarization of light is the formation of hydrogen bubbles on the particles of light. II. Plane polarization of light is the splitting of light into its spectral components III. Plane-polarized light vibrates in one plane only. IV. Polarization is characteristic of transverse waves.
- AI and III only
- BIII and IV onlyCorrect
- CI and II only
- DII and IV only
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Answer: B
Evaluating each statement:
- I — Incorrect. Formation of hydrogen bubbles describes electrolysis, not polarization.
- II — Incorrect. Splitting light into spectral components is dispersion, not polarization.
- III — Correct. Plane-polarized light has its electric field vibrating in one plane only.
- IV — Correct. Polarization is indeed a characteristic of transverse waves (light, microwaves) and cannot occur in longitudinal waves.
Therefore, only III and IV are correct.
- A
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6.In purely resistive a.c. circuit: I = I₀ sin ωt and V = V₀ sin ωt. Calculate instantaneous power dissipated in time t.
- AI₀V₀ sin(ωt)
- B½ I₀V₀
- CI₀V₀ sin²(ωt)Correct
- DI₀V₀
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Answer: C
In a purely resistive a.c. circuit, current and voltage are in phase. Instantaneous power is:
P = IV = [I₀ sin(ωt)][V₀ sin(ωt)] = I₀V₀ sin²(ωt)
Note: ½I₀V₀ is the average power, not the instantaneous value.
- A
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7.The expansion of solids can be considered a disadvantage in the
- Ariveting of metal plates
- Bfitting of metal tyres on wooden wheels
- Cconstruction of bimetallic strip thermometers
- Dlaying of railway linesCorrect
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Answer: D
Thermal expansion of solids is disadvantageous in the laying of railway lines because the rails expand during hot weather. If no expansion gaps are left between rail sections, the rails buckle under compressive stress, which can derail trains.
In contrast, expansion is exploited advantageously in: fitting metal tyres (heated to expand, then cooled to grip the wheel), riveting (hot rivet contracts to grip plates), and bimetallic strips (differential expansion drives the strip to bend for thermostats).
- A
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8.The phenomenon of radioactivity was first discovered by
- AWilhelm Röntgen
- BErnest Rutherford
- CMarie Curie
- DHenri BecquerelCorrect
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Answer: D
Radioactivity was first discovered by Henri Becquerel in 1896. He observed that uranium salts spontaneously emitted penetrating radiation that could expose a photographic plate, even in the dark.
Marie Curie later coined the term 'radioactivity' and discovered polonium and radium; Rutherford characterized the radiation types; Röntgen discovered X-rays.
- A
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9.A vector diagram shows resistance R, capacitive reactance Xc, inductive reactance XL and impedance Z in an R-L-C circuit. Current will be maximum when
- AZ = XL + XC
- BXL = XCCorrect
- CR = XL + XC
- DXL > XC
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Answer: B
In an R-L-C series circuit, the impedance is given by:
Z = √(R² + (XL − XC)²)
Current I = V/Z is maximum when Z is minimum, which occurs when the reactive component (XL − XC) = 0, i.e., when:
XL = XC
At this condition (called resonance), Z = R (its minimum value), and the circuit behaves as a purely resistive circuit.
- A
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10.Calculate the escape velocity of a satellite launched from earth's surface (g = 10 ms⁻², Earth's radius = 6.4 x 10⁶ m)
- A6.4 × 10³ m/s
- B1.60 × 10⁴ m/s
- C8.0 × 10³ m/s
- D1.13 × 10⁴ m/sCorrect
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Answer: D
Escape velocity is derived by equating kinetic energy to gravitational potential energy:
ve = √(2gR)
ve = √(2 × 10 × 6.4 × 10⁶) = √(1.28 × 10⁸) ≈ 1.13 × 10⁴ m/s
- A
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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Practise all 52 questions we hold from the 1993 paper, on a timed CBT screen
Every question has the answer and an explanation, in the Skolra app.