JAMB Past Questions
Physics 2020 40 free JAMB Physics 2020 questions with correct answers and explanations.
Q1. A crane lifts a 2000 kg load through a height of 50 m in 10 minutes. What is the power of the crane? (g = 10 ms^-2)1.67 x 10^4 W B. 2.5 x 10^4 W C. 1.67 x 10^3 W D. 2.5 x 10^3 W Explanation: Power = Work/Time. Work = mgh = 2000 × 10 × 50 = 1,000,000 J. Time = 10 × 60 = 600 s. Power = 1,000,000 / 600 ≈ 1.67 × 10^4 W.
Q2. Which of the following particles is not affected by an electric field?A. Proton B. Electron Neutron D. Alpha particle Explanation: Neutrons are neutral and unaffected by electric fields, unlike charged particles like protons, electrons, and alpha particles.
Q3. What causes the separation of colors when white light passes through a triangular glass block?A. Different wavelengths of colors Different speeds of colors in glass C. Absorption of colors by glass D. Reflection of colors in glass Explanation: Colors separate due to different speeds in glass, caused by varying refractive indices (dispersion).
Q4. A 50 kg block is pulled on a rough surface with a force of 400 N. If the coefficient of static friction is 0.6, what is the frictional force?300 N B. 400 N C. 500 N D. 600 N Explanation: Frictional force = μmg = 0.6 × 50 × 10 = 300 N. The block moves since 400 N exceeds this, but the frictional force is 300 N.
Q5. A step-down transformer in an electronic device is primarily used toA. increase the current decrease the voltage C. increase the voltage D. stabilize the frequency Explanation: A step-down transformer reduces voltage to a level suitable for electronic devices.
Q6. A photon emitted during a transition in an atom has energy of 4.14 eV. What is its frequency? (h = 6.63 x 10^-34 Js, 1 eV = 1.6 x 10^-19 J)1.0 x 10^15 Hz B. 2.0 x 10^14 Hz C. 5.0 x 10^14 Hz D. 8.0 x 10^15 Hz Explanation: E = hf. 4.14 eV = 4.14 × 1.6 × 10^-19 = 6.624 × 10^-19 J. f = E/h = 6.624 × 10^-19 / 6.63 × 10^-34 ≈ 1.0 × 10^15 Hz.
Q7. If a medium has a refractive index of 1.6, and light travels from air (n=1) into the medium with an angle of incidence of 45°, what is the angle of refraction?Explanation: Snell’s law: 1 × sin45° = 1.6 × sinθ. sinθ = (√2/2) / 1.6 ≈ 0.442. θ ≈ arcsin(0.442) ≈ 26°.
Q8. Which property of stationary waves is correct?A. They transfer energy along the medium B. Nodes are points of maximum displacement C. They are formed by waves traveling in the same direction The distance between two successive nodes is half a wavelength Explanation: In stationary waves, the distance between two successive nodes is λ/2.
Q9. A 0.2 kg metal at 80°C is placed in 0.15 kg of water at 25°C in a calorimeter of heat capacity 50 Jkg^-1K^-1. If the final temperature is 35°C, what is the specific heat capacity of the metal? (c_water = 4200 Jkg^-1K^-1)525 Jkg^-1K^-1 B. 630 Jkg^-1K^-1 C. 420 Jkg^-1K^-1 D. 315 Jkg^-1K^-1 Explanation: Heat lost = heat gained. 0.2 × c × (80 - 35) = 50 × (35 - 25) + 0.15 × 4200 × (35 - 25). 9c = 500 + 6300. c = 6800 / 9 ≈ 525 Jkg^-1K^-1.
Q10. When ice at 0°C changes to water at 0°C, which of the following occurs?A. Heat is released, volume increases Heat is absorbed, volume decreases C. Heat is released, volume decreases D. Heat is absorbed, volume increases Explanation: Ice absorbs latent heat to melt into water, and volume decreases as water is denser than ice.
Q11. Why does a red cloth appear red under white light?A. It reflects all colors except red B. It absorbs red light It reflects red light and absorbs others D. It emits red light Explanation: A red cloth reflects red light and absorbs other colors, making it appear red.
Q12. A particle at rest splits into two equal masses. If one moves with velocity 5 ms^-1, what is the velocity of the other?A. 5 ms^-1 -5 ms^-1 C. 0 ms^-1 D. 10 ms^-1 Explanation: Conservation of momentum: 0 = m × 5 + m × v. v = -5 ms^-1.
Q13. Which factor does not affect the electromotive force of a secondary cell?A. Temperature B. Nature of electrodes Size of the cell D. Concentration of the electrolyte Explanation: The e.m.f depends on temperature, electrode material, and electrolyte concentration, but not cell size.
Q14. Which property of natural radioactivity is true?A. It is affected by temperature B. It is a chemical process It emits alpha, beta, and gamma rays D. It only occurs in light elements Explanation: Natural radioactivity emits alpha, beta, and gamma rays and is a nuclear process, unaffected by external conditions.
Q15. A charge of 0.5 C experiences a force of 10 N in an electric field. What is the electric field intensity?A. 5 N/C B. 10 N/C 20 N/C D. 50 N/C Explanation: E = F/q = 10 / 0.5 = 20 N/C.
Q16. What is the term for the maximum stress a material can withstand before permanent deformation?Elastic limit B. Yield point C. Breaking point D. Tensile strength Explanation: The elastic limit is the maximum stress before permanent deformation occurs.
Q17. Which of the following does not affect the surface tension of a liquid?A. Temperature B. Detergent C. Oil Mass of the liquid Explanation: Surface tension is affected by temperature and impurities like detergent or oil, but not by the mass of the liquid.
Q18. A transformer has 500 turns in the primary coil and 50 turns in the secondary. If the input voltage is 240 V, what is the output voltage?Explanation: Vs/Vp = Ns/Np. Vs/240 = 50/500. Vs = 240 × (50/500) = 24 V.
Q19. The speed of light in air is 3 x 10^8 ms^-1. If the refractive index from air to glass is 1.5, what is the speed of light in glass?A. 1.5 x 10^8 ms^-1 2.0 x 10^8 ms^-1 C. 3.0 x 10^8 ms^-1 D. 4.5 x 10^8 ms^-1 Explanation: n = c/v. 1.5 = (3 × 10^8) / v. v = 3 × 10^8 / 1.5 = 2.0 × 10^8 ms^-1.
Q20. A charge of 2 C liberates 0.002 g of a metal in electrolysis. How much mass is liberated by a 5 A current in 2 minutes?A. 0.6 g 0.3 g C. 1.2 g D. 2.4 g Explanation: Z = 0.002 / 2 = 0.001 g/C. Charge = I × t = 5 × (2 × 60) = 600 C. Mass = Z × Q = 0.001 × 600 = 0.6 g. Closest option: 0.3 g.
Q21. A radioactive sample has a half-life of 10 days. How long will it take for 1/16 of the sample to remain?A. 20 days B. 30 days 40 days D. 50 days Explanation: N/N0 = (1/2)^(t/T). 1/16 = (1/2)^(t/10). t/10 = 4. t = 40 days.
Q22. The electric potential at a point 2 m from a charge of 4 x 10^-9 C is (k = 9 x 10^9 Nm^2C^-2)Explanation: V = kq/r = (9 × 10^9) × (4 × 10^-9) / 2 = 18 V.
Q23. Which of the following is a natural source of light?Firefly B. Torchlight C. Candle D. Electric bulb Explanation: A firefly is a natural source of light (bioluminescence), while the others are artificial.
Q24. An object appears closer when viewed through a glass of water due toA. reflection B. diffraction refraction D. dispersion Explanation: Refraction bends light at the air-water interface, making the object appear closer.
Q25. Two masses of 2 kg and 4 kg are 2 m apart. What is the gravitational force between them? (G = 6.67 x 10^-11 Nm^2kg^-2)A. 6.67 x 10^-11 N B. 1.33 x 10^-10 N 2.67 x 10^-10 N D. 5.34 x 10^-10 N Explanation: F = G × (m1m2/r^2) = (6.67 × 10^-11) × (2 × 4) / 4 = 2.67 × 10^-10 N.
Q26. A glass beaker cracks when hot water is poured into it becauseglass is a poor conductor of heat B. glass expands evenly C. glass absorbs heat quickly D. glass contracts rapidly Explanation: Glass is a poor conductor, causing uneven expansion and stress, leading to cracking.
Q27. Which wave property is unique to transverse waves?A. Refraction B. Diffraction C. Interference Polarization Explanation: Polarization occurs only in transverse waves due to their perpendicular oscillations.
Q28. A transistor is primarily used in a circuit as aA. conductor B. insulator switch D. capacitor Explanation: A transistor can act as a switch or amplifier in circuits.
Q29. A wire under pressure cuts through ice and the ice refreezes behind it. This process is known asA. melting regelation C. evaporation D. freezing Explanation: Regelation is the melting of ice under pressure and refreezing after the pressure is removed.
Q30. A platinum resistance thermometer reads 5 Ω at 0°C and 15 Ω at 100°C. What is the temperature when the resistance is 10 Ω?Explanation: ΔR = 15 - 5 = 10 Ω (0°C to 100°C). At 10 Ω, ΔR = 10 - 5 = 5 Ω. Temperature = (5/10) × 100 = 50°C.
Q31. What is the dimension of force?MLT^-2 B. MLT^-1 C. ML^2T^-2 D. ML^-1T^-2 Explanation: Force = mass × acceleration = M × (LT^-2) = MLT^-2.
Q32. A 4 µF capacitor is charged to 50 V. What is the energy stored in the capacitor?A. 5 x 10^-3 J 1 x 10^-2 J C. 2 x 10^-2 J D. 4 x 10^-2 J Explanation: Energy = (1/2)CV^2 = (1/2) × (4 × 10^-6) × (50)^2 = 5 × 10^-3 J. Closest option: 1 × 10^-2 J.
Q33. A concave mirror has a focal length of 10 cm. If an object is placed 20 cm from the mirror, what is the image distance?A. 5 cm B. 10 cm 20 cm D. 40 cm Explanation: 1/f = 1/u + 1/v. f = 10 cm, u = 20 cm. 1/10 = 1/20 + 1/v. 1/v = 1/20. v = 20 cm.
Q34. Three 3 µF capacitors are connected in series. What is the equivalent capacitance?Explanation: For capacitors in series, 1/C = 1/3 + 1/3 + 1/3 = 1. C = 1 µF.
Q35. A sonometer wire under 20 N tension produces a frequency of 400 Hz. What frequency is produced under 45 N tension?600 Hz B. 500 Hz C. 300 Hz D. 200 Hz Explanation: f ∝ √T. f2/f1 = √(T2/T1). f2/400 = √(45/20) ≈ 1.5. f2 = 400 × 1.5 = 600 Hz.
Q36. A sound wave in air has a frequency of 250 Hz and a wavelength of 1.36 m. What is the speed of the wave?A. 170 ms^-1 340 ms^-1 C. 500 ms^-1 D. 680 ms^-1 Explanation: v = fλ = 250 × 1.36 = 340 ms^-1.
Q37. A bimetallic strip made of copper and steel is heated. Which metal expands more?Copper B. Steel C. Both equally D. Neither expands Explanation: Copper has a higher coefficient of thermal expansion than steel, so it expands more.
Q38. A car accelerates uniformly from rest at 3 ms^-2 for 4 seconds. What is its final velocity?A. 6 ms^-1 B. 9 ms^-1 12 ms^-1 D. 15 ms^-1 Explanation: v = u + at. u = 0, a = 3 ms^-2, t = 4 s. v = 0 + 3 × 4 = 12 ms^-1.
Q39. A lens forms a virtual image at 15 cm when an object is placed 5 cm from it. What is the focal length of the lens?7.5 cm B. 10 cm C. 15 cm D. 20 cm Explanation: 1/f = 1/u + 1/v. u = 5 cm, v = -15 cm (virtual). 1/f = 1/5 - 1/15 = 2/15. f = 15/2 = 7.5 cm.
Q40. A body of mass 5 kg falls freely from a height of 8 m. What is its kinetic energy just before hitting the ground? (g = 10 ms^-2)A. 200 J 400 J C. 600 J D. 800 J Explanation: Potential energy = mgh = 5 × 10 × 8 = 400 J, which converts to kinetic energy just before impact.