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JAMB Physics 2025 Past Questions & Explanations

Try 20 of 35+ JAMB Physics 2025 questions as a free quiz — select your answers, submit, and see your score with a full explanation for every one.

  1. 1.
    Which device operates based on the magnetic effect produced by an electric current?
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    An electric bell operates based on the magnetic effect of electric current. When current flows through a coil wound around an iron core, it creates a magnetic field that attracts an armature, which strikes a bell. This is a direct application of electromagnetism. A rheostat is a variable resistor, a thermostat is a temperature control device, and a carbon microphone converts sound to electrical signals—none rely on the magnetic effect of current.
  2. 2.
    What mass of silver will be deposited during electrolysis when a current of 0.8 A flows for 25 minutes?
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    m=MItFm=\frac{MIt}{F}

    t=25×60=1500,st=25\times60=1500,s

    m=108×0.8×150096500m=\frac{108\times0.8\times1500}{96500}

    m=12960096500=1.34,gm=\frac{129600}{96500}=1.34,g

    m=1.34,g\boxed{m=1.34,g}

  3. 3.
    The gravitational force between two masses P and Q is 10 N. What will be the force if both masses are doubled while the distance remains unchanged?
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    Newton's law of universal gravitation states: F=Gm1m2r2F = \frac{Gm_1m_2}{r^2}. If both masses are doubled (m₁ → 2m₁ and m₂ → 2m₂) while distance r remains constant, the new force becomes: Fnew=G(2m1)(2m2)r2=4×Gm1m2r2=4FF_{new} = \frac{G(2m_1)(2m_2)}{r^2} = 4 \times \frac{Gm_1m_2}{r^2} = 4F. Since the original force was 10 N, the new force is 4 × 10 = 40 N.
  4. 4.
    A wooden block has a relative density of 0.4 and floats in a liquid whose density is 1600 kg m⁻³. What proportion of the block's volume remains submerged?
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    For a floating body, the principle of buoyancy states: Weight = Upthrust. Mass of block × g = Mass of liquid displaced × g. If the block's density is relative density 0.4, and the liquid's density is 1600 kg/m³, then the block's density = 0.4 × 1600 = 640 kg/m³. For equilibrium: (density of block/density of liquid) = (volume submerged/total volume). Proportion submerged = 640/1600 = 0.4. However, relative density is typically given as density/density of water (1000 kg/m³), so block density = 0.4 × 1000 = 400 kg/m³. Proportion submerged = 400/1600 = 0.25.
  5. 5.
    When a positively charged rod is brought near the cap of the electroscope shown, what happens to the divergence of the leaves?
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    When a positively charged rod approaches the metallic cap of an electroscope, positive charge is repelled and accumulates on the cap and leaves. Since both leaves now carry the same positive charge, they repel each other mutually, causing the divergence (angle between the leaves) to increase. The leaves spread further apart due to electrostatic repulsion between like charges.
  6. 6.
    The functioning of a photovoltaic cell depends on the action of which material?
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    A photovoltaic cell converts light energy directly into electrical energy through the photovoltaic effect. This effect occurs in semiconductor materials (like silicon), where photons excite electrons from the valence band to the conduction band, creating a potential difference. Conductors have free electrons already and don't require photon excitation. Insulators block electron flow. While chemical reactions may occur, the primary physics depends on the semiconductor material's band structure.
  7. 7.
    What is the expression for the power of a lens in diopters?
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    The power P of a lens is defined as the reciprocal of its focal length (f) expressed in meters: P=1fP = \frac{1}{f} (in diopters). A lens with focal length 0.5 m has power 1/0.5 = 2 D. A positive (converging) lens has positive power; a negative (diverging) lens has negative power. This is the fundamental definition used in lens optics.
  8. 8.
    At what distance from a point charge of 1.2×10−71.2 \times 10^{-7} C will the electric field intensity be 4.8×10−44.8 \times 10^{-4} N C⁻¹? [Take 14πε0=9.0×109\frac{1}{4\pi\varepsilon_0} = 9.0 \times 10^9]
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    The electric field intensity due to a point charge is: E=14πε0×Qr2E = \frac{1}{4\pi\varepsilon_0} \times \frac{Q}{r^2}. Rearranging for distance: r=14πε0×QEr = \sqrt{\frac{1}{4\pi\varepsilon_0} \times \frac{Q}{E}}. Substituting values: r=9.0×109×1.2×10−74.8×10−4=9.0×109×2.5×10−4=2.25×106=1.5×103r = \sqrt{9.0 \times 10^9 \times \frac{1.2 \times 10^{-7}}{4.8 \times 10^{-4}}} = \sqrt{9.0 \times 10^9 \times 2.5 \times 10^{-4}} = \sqrt{2.25 \times 10^6} = 1.5 \times 10^3 m = 1.5 km.
  9. 9.
    Find the heat capacity of a material that absorbs 48 kJ of heat when its temperature increases by 53ºC.
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    Heat capacity C is defined as: C=QΔTC = \frac{Q}{\Delta T}, where Q is heat absorbed and ΔT is temperature change. Converting: Q = 48 kJ = 48,000 J, and ΔT = 53 K (or 53ºC, since a change is the same on both scales). Therefore: C=4800053≈905.7C = \frac{48000}{53} ≈ 905.7 J K⁻¹. This represents the total amount of heat needed to raise the temperature of the material by 1 K.
  10. 10.
    A body moves with an initial velocity of 4 m/s. After accelerating at 5 m/s² for 2 s, its impulse is 60 kg m s⁻¹. Find its mass.
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    Impulse J = Δ(momentum) = m × Δv. First, find the change in velocity: Δv = a × t = 5 × 2 = 10 m/s. The final velocity is v_f = 4 + 10 = 14 m/s, so Δv = 14 - 4 = 10 m/s. Using J = m × Δv: 60 = m × 10, therefore m = 60/10 = 6 kg. Alternatively, impulse can be calculated as J = F × t = (m × a) × t = m × a × t, giving 60 = m × 5 × 2, so m = 6 kg.
  11. 11.
    5400 kJ of heat is released when steam condenses to form water at 15ºC. Calculate the mass of water obtained. [Lv=2.26×106L_v = 2.26 \times 10^6 J kg⁻¹, cw=4200c_w = 4200 J kg⁻¹ K⁻¹]
    Show explanation
    The problem involves two processes: (1) Condensation of steam to water at 100ºC, releasing latent heat; (2) Cooling of water from 100ºC to 15ºC. Total heat released = 5400 kJ = 5,400,000 J. Heat from condensation: Q1=m×Lv=m×2.26×106Q_1 = m × L_v = m × 2.26 \times 10^6. Heat from cooling: Q2=m×cw×ΔT=m×4200×(100−15)=m×4200×85=357,000mQ_2 = m × c_w × \Delta T = m × 4200 × (100 - 15) = m × 4200 × 85 = 357,000m. Total: 2.26×106m+357,000m=5,400,0002.26 \times 10^6 m + 357,000m = 5,400,000. So 2,617,000m=5,400,0002,617,000m = 5,400,000, giving m=2.06m = 2.06 kg.
  12. 12.
    A short-sighted person has a far point of 95 cm. Which lens can correct this defect?
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    Myopia (short-sightedness) is corrected using a diverging (concave) lens. The far point of 95 cm means objects beyond this distance appear blurred. The corrective lens should have a focal length equal to the far point distance. A diverging lens of focal length f = 95 cm will form a virtual image at the far point for objects at infinity, allowing the eye to see distant objects clearly. A mirror cannot be used for vision correction in the conventional sense, a plano-convex lens is convergent (not divergent), and a converging lens worsens myopia.
  13. 13.
    What is the dimensional formula for tension in a string?
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    Tension is a force, and the dimensional formula for force is derived from Newton's second law: F=maF = ma. Mass [M] has dimension M, and acceleration [a] has dimension LT−2LT^{-2}. Therefore, force has dimension M×LT−2=MLT−2M × LT^{-2} = MLT^{-2}. Tension, being a force, has the same dimensional formula: MLT−2MLT^{-2}. This can be verified by considering that tension = force = mass × acceleration.
  14. 14.
    If an object sinks in water, it implies that:
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    An object sinks in water when the gravitational force (weight) exceeds the buoyant force (upthrust). According to Archimedes' principle, upthrust depends on the volume of water displaced. For an object to sink, its weight must be greater than the maximum possible upthrust it can experience when fully submerged. This occurs when the object's density exceeds water's density (1000 kg/m³). When density is less, the upthrust (from displaced water) exceeds weight, causing floating. Option B is false because upthrust equals weight only at equilibrium (floating or suspension). Option D confuses pressure with force.
  15. 15.
    A gas at constant pressure is cooled from 57ºC and its volume reduces to one-fifth of its original volume of 2.00 cm³. Determine the new temperature.
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    P=constant,V1T1=V2T2P=\text{constant},\quad \frac{V_1}{T_1}=\frac{V_2}{T_2}

    T1=57+273=330,K,V2=15V1T_1=57+273=330,\text{K},\quad V_2=\frac{1}{5}V_1

    V1330=V1/5T2⇒T2=3305=66,K\frac{V_1}{330}=\frac{V_1/5}{T_2}\Rightarrow T_2=\frac{330}{5}=66,\text{K}

    T2=66−273=−207∘CT_2=66-273=-207^\circ\text{C}

    T2=−207∘C\boxed{T_2=-207^\circ\text{C}}

  16. 16.
    A circular parallel plate capacitor has a radius of 6 cm and plate separation of 0.12 cm. Calculate its capacitance. [π=3.142\pi = 3.142, ε0=8.85×10−12\varepsilon_0 = 8.85 \times 10^{-12} F/m]
    Show explanation
    The capacitance of a parallel plate capacitor is: C=ε0AdC = \varepsilon_0 \frac{A}{d}, where A is the plate area and d is the separation. Convert units to SI: radius r = 6 cm = 0.06 m, separation d = 0.12 cm = 0.0012 m. Calculate area: A=πr2=3.142×(0.06)2=3.142×0.0036=0.01131A = \pi r^2 = 3.142 × (0.06)^2 = 3.142 × 0.0036 = 0.01131 m². Calculate capacitance: C=8.85×10−12×0.011310.0012=8.85×10−12×9.425=8.35×10−11C = 8.85 × 10^{-12} × \frac{0.01131}{0.0012} = 8.85 × 10^{-12} × 9.425 = 8.35 × 10^{-11} F ≈ 8.3×10−118.3 × 10^{-11} F.
  17. 17.
    The graph of pressure against temperature is a straight line through the origin only when temperature is measured on which scale?
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    Pressure is directly proportional to absolute temperature at constant volume. A pressure-temperature graph passes through the origin only when temperature is measured on the Kelvin (thermodynamic) scale.

  18. 18.
    A reservoir has a length of 10m and a breadth of 5m. If the total weight of water in it is 5000N, calculate the pressure exerted at the bottom.
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    Pressure is defined as force per unit area: P=FAP = \frac{F}{A}. The force is the weight of water = 5000N. The area of the bottom = length × breadth = 10m × 5m = 50m². Therefore, P=500050=100PaP = \frac{5000}{50} = 100Pa. Option C is correct. Options A, B, and D result from incorrect area calculations or arithmetic errors.
  19. 19.
    A positively charged particle of charge 5 μC moves with a speed of 3 × 10⁴m/s at an angle of 45º to a magnetic field. If the magnetic force acting on it is 6N, calculate the magnetic flux density.
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    The magnetic force on a moving charged particle is given by: F=qvBsin⁡θF = qvB\sin\theta, where q is charge, v is velocity, B is magnetic flux density, and θ is the angle between velocity and field. Rearranging: B=Fqvsin⁡θB = \frac{F}{qv\sin\theta}. Substituting values: B=6(5×10−6)(3×104)sin⁡45°=6(5×10−6)(3×104)(0.7071)=60.1061≈56.57TB = \frac{6}{(5 \times 10^{-6})(3 \times 10^4)\sin 45°} = \frac{6}{(5 \times 10^{-6})(3 \times 10^4)(0.7071)} = \frac{6}{0.1061} \approx 56.57T. Option D is correct.
  20. 20.
    A refrigerator has a power rating of 150W and operates continuously for 336 hours. Calculate the electrical energy used in kilowatt-hours.
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    Electrical energy is calculated as: E=PtE = Pt, where P is power in kilowatts and t is time in hours. Converting power: 150W = 0.150kW. Therefore: E=0.150×336=50.4kWhE = 0.150 \times 336 = 50.4kWh. Option C is correct. The other options result from incorrect unit conversions or arithmetic errors.
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