WAEC Physics 2020 past questions

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

Ten questions from the 2020 WAEC Physics paper, with answers and explanations. We hold 48 questions from this paper, and the Skolra app has all of them.

WAEC Physics 2020 questions and answers

1. 1.

   An electron of mass 9.1x 10$^{31}$ kg is travelling at a speed of 2.0 x 10$^6$ms$^{-1}$.Calculate the associate wavelength of the electron. [h = 6.6. x 10$^{34}$ Js]

   1. A
      1.2 × 10⁻¹⁰ m
   2. B
      3.6 × 10⁻⁸ m
   3. C
      2.8 × 10⁻¹⁰ m
   4. D
      3.6 × 10⁻¹⁰ m
      Correct
   Show answerHide answer

   Answer: D

   Using de Broglie's equation: λ = h/(mv)
   λ = (6.6 × 10⁻³⁴) / (9.1 × 10⁻³¹ × 2.0 × 10⁶)
   λ = 6.6 × 10⁻³⁴ / (18.2 × 10⁻²⁵)
   λ = (6.6/18.2) × 10⁻³⁴⁺²⁵
   λ = 0.363 × 10⁻⁹ m
   λ ≈ 3.6 × 10⁻¹⁰ m

2. 2.

   Which of the following statements about photoelectrons is correct?

   1. A
      their emission continues regardless of the frequency of light used
   2. B
      their maximum kinetic energy depends on the frequency of incident radiation
      Correct
   3. C
      they are emitted only when the metal surface is heated to a high temperature
   4. D
      their number increases with the frequency of incident radiation
   Show answerHide answer

   Answer: B

   Einstein's photoelectric equation: KE_max = hf − φ
   The maximum kinetic energy of photoelectrons depends directly on the frequency f of the incident radiation. Higher-frequency photons transfer more energy. The number of emitted electrons depends on intensity (not frequency). Emission stops below the threshold frequency regardless of intensity, so option a is false.

3. 3.

   Which of the following machinesdoes not apply the lever principle?

   1. A
      wheelbarrow
   2. B
      hydraulic press
      Correct
   3. C
      crowbar
   4. D
      scissors
   Show answerHide answer

   Answer: B

   The hydraulic press operates on Pascal's principle — pressure applied to an enclosed fluid is transmitted equally in all directions — not the lever principle. Scissors (fulcrum at the pivot), wheelbarrow (axle as fulcrum), and crowbar (pivot point as fulcrum) all work as levers with a defined fulcrum, effort arm, and load arm. The hydraulic press uses the ratio of piston areas to multiply force.

4. 4.

   A ray of light travels obliquely from a less dense medium to a denser medium. Which of the following statements is true about the light?

   1. A
      it speeds up and bends away from the normal
   2. B
      its frequency increases on entering the denser medium
   3. C
      its wavelength increases on entering the denser medium
   4. D
      it slows down and bends toward the normal
      Correct
   Show answerHide answer

   Answer: D

   When light travels from a less dense to a denser medium:
   1. Its speed decreases (refractive index n = c/v; denser medium has higher n, so v is smaller).
   2. It bends toward the normal (angle of refraction < angle of incidence — Snell's law).
   Frequency is set by the source and remains unchanged. Wavelength decreases proportionally with speed (since v = fλ and f is constant).

5. 5.

   The magnitude of the force experienced by a charge of 1.6 x 10$^{-8}$C in a uniform electric field of intensity 5 x 105NC$^{-1}$is

   1. A
      8.0 × 10⁻² N
   2. B
      8.0 × 10³ N
   3. C
      8.0 × 10⁻³ N
      Correct
   4. D
      3.2 × 10⁻¹³ N
   Show answerHide answer

   Answer: C

   Using F = qE:
   F = 1.6 × 10⁻⁸ × 5 × 10⁵
   F = (1.6 × 5) × 10⁽⁻⁸⁺⁵⁾
   F = 8.0 × 10⁻³ N
   The magnitude of the electric force on the charge is 8.0 × 10⁻³ N (8 mN).

6. 6.

   Which of the following statements about the process of melting of a solid are true? The temperature of the solid will

   I. remain steady until melting starts.

   ll. keep rising until melting starts,

   Ill remain steady as melting proceeds.

   V, keep rising as melting proceeds.

   1. A
      I and II only
   2. B
      II and III only
      Correct
   3. C
      III and IV only
   4. D
      I and III only
   Show answerHide answer

   Answer: B

   During the melting of a solid:
   • Statement II is true: temperature keeps rising as heat is supplied, until the melting point is reached.
   • Statement III is true: once melting begins, temperature stays constant (at the melting point) while the supplied energy breaks intermolecular bonds (latent heat).
   • Statement I is false — temperature does not stay steady before melting; it rises.
   • Statement V is false — temperature does not rise while melting is in progress.

7. 7.

   Which of the following statement about viscosity is not true? it

   1. A
      is a property of fluids only
   2. B
      increases with temperature rise in liquids
      Correct
   3. C
      arises from intermolecular cohesive forces
   4. D
      decreases with temperature rise in liquids
   Show answerHide answer

   Answer: B

   For liquids, viscosity decreases with increasing temperature because intermolecular cohesive forces weaken as molecules gain kinetic energy. The statement that viscosity increases with temperature rise is not true for liquids. (For gases, viscosity does increase with temperature due to increased momentum transfer between layers.)

8. 8.

   Which of the following units is not fundamental?

   1. A
      metre
   2. B
      Newton
      Correct
   3. C
      second
   4. D
      kilogram
   Show answerHide answer

   Answer: B

   The Newton (N) is a derived unit defined as kg·m·s⁻². It is not one of the seven fundamental (base) SI units. The kilogram (mass), metre (length), and second (time) are all fundamental SI base units. Derived units are expressed as combinations of base units.

9. 9.

   A luminous object is one that

   1. A
      absorbs all incident light
   2. B
      allows light to pass through it
   3. C
      produces its own light
      Correct
   4. D
      reflects light from another source
   Show answerHide answer

   Answer: C

   A luminous object is one that produces or emits its own light. Examples include the Sun, stars, candle flames, and electric bulbs. Objects that only reflect external light (such as the Moon) are non-luminous. Absorbing all light describes a perfect black body, and allowing light through describes a transparent medium.

10. 10.

    Which of the following statements explain why hot soapy wateris more effective in cleaning oil-stained dishes?

    1. A
       Hot water has a higher surface tension that forces water into grease
    2. B
       Soap increases the boiling point of water, preventing evaporation during washing
    3. C
       Hot water increases the viscosity of oil, making it easier to remove
    4. D
       Soap reduces surface tension and hot water provides energy to emulsify the oil
       Correct
    Show answerHide answer

    Answer: D

    Soap molecules are amphiphilic — their hydrophobic tails embed in oil while their hydrophilic heads face the water, forming micelles that lift oil off surfaces (emulsification). Soap also lowers surface tension, allowing water to wet and spread over greasy surfaces. Heat from hot water additionally increases molecular kinetic energy, speeding up the emulsification process. Together these effects make hot soapy water far more effective at removing oil than cold water alone.

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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