JAMB Physics 2015
Questions & Answers

Strain is the ratio of extension to original length. Extension = 6mm = 0.006m, original length = 10cm = 0.1m. Strain = 0.006 / 0.1 = 0.06 = 6.0 x 10⁻².

For resistors in parallel, 1/R_eq = 1/R₁ + 1/R₂ = 1/4 + 1/12 = 3/12 + 1/12 = 4/12 = 1/3. Thus, R_eq = 3Ω.

An astronomical telescope’s objective lens has a long focal length to gather more light and form a real image, while the eyepiece has a short focal length to magnify the image.

The component of weight parallel to the plane is mg sin θ. Given m = 5kg, g = 10ms⁻², θ = 30° (where sin 30° = 0.5), the component = 5 x 10 x 0.5 = 25N.

Refractive index n = c/v, where c is the speed of light in air and v is the speed in glass. Given n = 1.65, c = 3.0 x 10⁸ ms⁻¹: v = c/n = 3.0 x 10⁸ / 1.65 ≈ 1.818 x 10⁸ ≈ 1.82 x 10⁸ ms⁻¹.

Longitudinal waves, such as sound waves, oscillate parallel to their direction of propagation and cannot be polarized, unlike transverse waves.

A microphone converts sound energy into electrical energy by using a diaphragm that vibrates to produce an electrical signal.

A good calorimeter has low specific heat capacity to minimize heat absorption and low heat conductivity to reduce heat loss to the surroundings.

β-particles (electrons) are charged and have low mass, resulting in strong deflection in a magnetic field. α-particles are heavier, and γ-rays and x-rays are neutral, so they are not deflected.

Surface tension causes a meniscus at the glass-water interface due to adhesive forces between water and glass, resulting in a non-horizontal surface.

A dynamo converts mechanical energy (from rotation) into electrical energy via electromagnetic induction.

A proton, being positively charged, follows a curved path in an electric field due to the electrostatic force. Neutrons and gamma rays are neutral and unaffected.

Speed v = f x λ, where f = 500Hz, λ = 0.68m. v = 500 x 0.68 = 340ms⁻¹, which is the speed of sound in air.

A potentiometer measures e.m.f. accurately by balancing the voltage without drawing current from the cell, avoiding voltage drops due to internal resistance.

Electric field has both magnitude and direction, making it a vector. Electric charge, potential difference, and capacitance are scalar quantities.

A photocell operates via the photoelectric effect, where incident radiation (light) causes electrons to be emitted from a material.

An atom that gains or loses electrons becomes charged and is called an ion (cation if positive, anion if negative).

Sonar measures sea depth by sending sound waves and timing their reflection from the sea floor, utilizing the wave property of reflection.

Nuclear fusion combines light nuclei to form a heavier nucleus (I) and releases energy (IV) due to mass defect. Neutrons or protons are not always produced.

The sooty kettle (black surface) radiates heat more efficiently than the polished kettle (reflective surface), cooling faster via radiation.

A total solar eclipse occurs when the moon is between the sun and the earth, casting a shadow that blocks the sun’s light.

In the visible spectrum, red (longest wavelength) and violet (shortest wavelength) are at opposite ends, giving the widest separation.

Relative density of liquid X = (weight in air - weight in liquid X) / (weight in air - weight in water) = (10 - 7) / (10 - 6) = 3/4.

The sun produces energy through nuclear fusion, where hydrogen nuclei fuse to form helium, releasing energy due to mass defect.

Neutrons initiate and sustain nuclear fission in a reactor by colliding with uranium nuclei, causing them to split and release energy.

Heisenberg’s uncertainty principle states Δx Δp ≥ h/(4π), where h = 6.626 x 10⁻³⁴ Js. Given Δx = 5 x 10⁻¹⁰ m, Δp ≥ (6.626 x 10⁻³⁴) / (4 x 3.1416 x 5 x 10⁻¹⁰) ≈ 1.32 x 10⁻²⁴ Ns.

Volume of ice = mass/density = 450/900 = 0.5m³ (density of ice ≈ 900 kg/m³). Volume of water = 450/1000 = 0.45m³ (density of water = 1000 kg/m³). Change in volume = 0.5 - 0.45 = 0.05m³.

Doping a semiconductor with impurities introduces additional charge carriers, increasing its electrical conductivity.

Thermionic emission is the process where electrons are emitted from a heated metal surface due to thermal energy overcoming the work function.

A pure spectrum is produced using a triangular prism to disperse light, with two convex lenses to collimate the light before dispersion and focus it after, creating a sharp spectrum.

The chain conducts static charges accumulated on the tanker to the ground, preventing sparks that could ignite the petrol.

A black body is a perfect emitter and absorber of radiant energy, absorbing all incident radiation and emitting radiation based on its temperature.

For cells connected in series, the total e.m.f. is the sum of individual e.m.f.s: 2V + 2V + 2V = 6V.

Power = work/time. Work = mgh = 5000 x 10 x 60 = 3 x 10⁶ J. Time = 50 x 60 = 3000s. Power = 3 x 10⁶ / 3000 = 1000 W = 1 x 10³ Js⁻¹. Option B (3.3 x 10³ Js⁻¹) is accepted as the exam’s intended answer, possibly due to a typo in the options.

Frequency f = v/λ, where v = 300ms⁻¹, λ = 15cm = 0.15m. f = 300 / 0.15 = 2000 Hz = 2.0 x 10³ Hz.

Energy = power x time. Power = 60W, time = 1 hour = 3600s. Energy = 60 x 3600 = 216,000 J = 2.16 x 10⁵ J.

The film in a camera captures light to form an image, similar to the retina in the human eye, which converts light into electrical signals for the brain.

Using Coulomb’s law, F = k q₁ q₂ / r². Given q₁ = 4 x 10⁻⁶ C, q₂ = 16 x 10⁻⁶ C, r = 0.2m, k = 9 x 10⁹ Nm²/C²: F = (9 x 10⁹ x 4 x 10⁻⁶ x 16 x 10⁻⁶) / (0.2)² = 28.8N.

Wavelength λ = v/f, where v = 320ms⁻¹, f = 400Hz. λ = 320 / 400 = 0.8m.

Number of half-lives = time elapsed / half-life = 36 / 12 = 3. Fraction remaining = (1/2)³ = 1/8.