JAMB Physics 2020 Past Questions & Answers

The correct answer is diffusion. Diffusion is the natural movement of particles from an area where they are highly concentrated to an area of lower concentration. In this case, the salt particles (ions) move from the area where they were dropped into the rest of the water until they are spread out evenly. This movement is caused by the random motion of both the salt particles and the water molecules.

Common mistake: Students often mistakenly choose 'convection' because it also involves movement in a fluid, but convection is the movement of the fluid itself due to density changes caused by heating, not the random spreading of particles within the fluid.

The force that keeps an object moving in a circular path is known as the centripetal force, and it always acts towards the center of the circle. This force is responsible for constantly changing the direction of the object's velocity, even if its speed is constant. The standard formula to calculate this force is F = mv²/r, where 'm' is the mass, 'v' is the velocity, and 'r' is the radius of the circular path.

Common mistake: Students may mistakenly choose option D (mv/r²) because they confuse the formula with inverse-square laws like Newton's law of gravitation, which has r² in the denominator.

This question is based on the principle of conservation of linear momentum, which states that the total momentum before an event equals the total momentum after. Before firing, the total momentum is zero. After firing, the bullet's forward momentum (mass × velocity) must be equal and opposite to the gun's backward momentum. The bullet's momentum is 0.05 kg × 100 m/s = 5 kg m/s, so the gun's momentum must also be 5 kg m/s, which gives a recoil speed of 5 kg m/s ÷ 5 kg = 1 m/s.

Common mistake: A common mistake is forgetting to convert the bullet's mass from 50g to 0.05kg before applying the momentum formula, which results in an incorrect answer.

The period of a simple pendulum (T) is related to its length (L) by the formula T = $2π√(L/g)$. This formula shows that the period is proportional to the square root of the length $(T ∝ √L)$. If the length is increased by a factor of four (L becomes 4L), the new period will be proportional to the square root of four, which is two. Therefore, the period is increased by a factor of 2.

Common mistake: Students often mistakenly think the period is directly proportional to the length, leading them to choose 4, but the relationship is with the square root of the length.

Most materials expand when they are heated and contract when they are cooled. However, water behaves unusually between 0°C and 4°C. In this specific temperature range, when water is heated from 0°C, it contracts instead of expanding, reaching its smallest volume and highest density at 4°C. This strange behaviour is known as the anomalous expansion of water.

Common mistake: Students often mistakenly choose -4°C to 0°C, confusing the temperature range for the anomalous behaviour of liquid water with temperatures below its freezing point.

The correct option is B because it accurately describes the fundamental properties of radioactive emissions. An alpha particle is a helium nucleus, giving it a positive charge. A beta particle is a high-speed electron, which is negatively charged. Gamma rays are high-energy electromagnetic radiation, like X-rays, and therefore have no charge (they are neutral).

Common mistake: Students may mistakenly choose option A by incorrectly thinking statement (iv) is true, perhaps confusing the properties of beta particles with alpha particles, which are helium nuclei.

The correct option is 'All of the above' because each statement is a valid concept in thermal physics. Statement A correctly defines temperature as the measure of the average kinetic energy of molecules. Statement B describes heat as the total internal energy of a system, and statement C correctly introduces the idea of specific heat capacity, where different substances require different amounts of heat for the same temperature rise.

Common mistake: A student might quickly choose option A because it is a very common and direct definition of temperature, without carefully evaluating that the other options are also correct statements related to heat and temperature.

First, calculate the current when the key K is open. The total resistance is 8Ω + 2Ω = 10Ω, so the initial current is I = V/R = 6V/10Ω = 0.6A. When the key K is closed, the two 8Ω resistors are in parallel, and their combined resistance is $(8*8)/(8+8)$ = 4Ω. This is in series with the 2Ω resistor, so the new total resistance is 4Ω + 2Ω = 6Ω. The new current is I = 6V/6Ω = 1.0A. The change in current is an increase of 1.0A - 0.6A = 0.4A.

Common mistake: Students might correctly calculate the initial current as 0.6A and then mistakenly choose an option like 'reduce the current by 0.6A' without calculating the final current and the actual change.

X-rays are high-energy electromagnetic waves with many important uses due to their ability to penetrate materials. They are used in hospitals to see bones inside the body, for treating cancer, and in industries to check for hidden cracks in metals. However, X-rays are not used for detecting fingerprints; fingerprints are surface patterns that are made visible using powders and visible light, not penetrating radiation like X-rays.

Common mistake: Students might get confused and think that because X-rays are used for detailed imaging in medicine and industry, they could also be used for the detailed patterns of fingerprints, but this is incorrect as fingerprints are a surface feature.

Natural radioactivity is the process by which an unstable atomic nucleus loses energy by emitting radiation. The three main types of radiation emitted during this spontaneous decay are alpha (α) particles, beta (β) particles, and gamma (γ) rays. Alpha and beta emissions change the composition of the nucleus, while gamma emission releases excess energy, often after an alpha or beta decay has occurred. Therefore, a complete description of natural radioactive emissions includes all three.

Common mistake: Students might mistakenly choose option A because they remember alpha and beta decay as the primary types of radioactive emission, but they forget that high-energy gamma rays are also frequently released during the process to bring the nucleus to a stable energy state.