JAMB Physics 2022 Past Questions & Answers

In Physics, we have fundamental units and derived units. Fundamental units are the basic building blocks of measurement, such as the kilogram (for mass), metre (for length), and second (for time). Derived units are created by combining these fundamental units; for example, the Newton is the unit of force, which is defined as mass times acceleration (kg⋅m/s²), making it a derived unit.

Common mistake: Students often confuse fundamental units with derived units, and may select options like Kilogram or Metre because they are very common, without realizing they are the basic building blocks and not derived from other units.

A fundamental property of magnets is that they always have two poles, a north and a south pole. When you cut a bar magnet, each piece instantly forms its own north and south pole, becoming a new, smaller magnet. This is because the tiny magnetic domains inside remain aligned in each piece, so you simply create two new magnets.

Common mistake: Students may incorrectly choose option D, believing that breaking the magnet will destroy its magnetic properties, a process known as demagnetization.

The general equation for a progressive wave is written as y = A sin(kx - ωt), where 'k' represents the wave number. When you compare this general formula to the equation given in the question, y = 5mm sin(1cm⁻¹x - 60s⁻¹t), you can see that the number multiplying the position 'x' is the wave number. Therefore, the wave number 'k' is 1 cm⁻¹, which is the same as 1.0 cm⁻¹.

Common mistake: Students often confuse the wave number (k), which is the coefficient of x, with the angular frequency (ω), which is the coefficient of t (60s⁻¹ in this case).

The principle of a pinhole camera is based on magnification, which relates the sizes and distances of the object and image. The formula is: (Image height / Object height) = (Image distance / Object distance). Using the values given, we have (20 cm / 40 cm) = (Image distance / 30 cm). This simplifies to 0.5 = (Image distance / 30 cm), which means the image distance is 0.5 multiplied by 30 cm, giving a result of 15 cm.

Common mistake: A common mistake is to incorrectly invert the distance ratio in the formula, for example setting it up as (Image height / Object height) = (Object distance / Image distance), which would lead to the wrong answer of 60 cm.

According to Faraday's Law of Electromagnetic Induction, a current is produced in a coil only when the magnetic field passing through it changes. This change is caused by relative motion between the magnet and the coil, such as moving the magnet towards or away from the coil. If there is no relative motion, the magnetic field is constant, so no current is induced, and the galvanometer pointer will not move.

Common mistake: Students may mistakenly choose options A, C, or D because they remember that motion is needed for induction, but they fail to notice the question asks for the condition where there is *no* deflection (no current).

Tyre treads are the grooves on the surface of a tyre designed to increase the force of friction between the tyre and the road. This increased friction provides the grip needed for the car to accelerate, brake, and turn safely. On wet roads, the treads also help to channel water away, preventing the car from sliding and ensuring good contact with the road surface.

Common mistake: Students might mistakenly choose option C, 'increase its longevity', because the depth of the tread is used to determine when a tyre is worn out, but the primary purpose of the tread design itself is to provide grip through friction.

To solve this, we use the equation of motion: s = ut + ½at². Since the car starts from rest, its initial velocity (u) is 0. Substituting the given values, we get 40 = $(0 * 10)$ + ½ * a * (10)², which simplifies to 40 = 50a. To find the acceleration (a), we divide 40 by 50, which gives us 0.80 ms⁻².

Common mistake: Students might mistakenly calculate the average velocity (distance/time) instead of acceleration, leading them to incorrectly choose 4.00 ms⁻².

When a solid object is heated, it expands in all three dimensions (length, width, and height). The coefficient of linear expansion (α) describes the expansion in one dimension, while the coefficient of volumetric expansion (γ) describes the expansion of the total volume. For a solid that expands equally in all directions, the volumetric expansion is approximately three times the linear expansion, which gives the relationship γ = 3α.

Common mistake: Students often mistakenly choose γ = α³ because they confuse the relationship between the expansion coefficients with the geometric formula for volume (V = L³).

In a simple primary cell, the formation of hydrogen bubbles on the positive copper plate is a defect called polarization. This process increases the internal resistance of the cell and reduces its overall voltage. Local action is a completely different defect caused by impurities in the negative zinc plate, which makes the zinc dissolve even when the cell is not in use. Therefore, local action is not a result of the hydrogen bubbles on the copper plate.

Common mistake: Students often confuse the two main defects of a primary cell, polarization and local action, without knowing that polarization happens at the positive plate while local action happens at the negative plate.

The 'lost voltage' of a cell refers to the potential difference across its internal resistance, which is the voltage used up inside the cell itself. It is calculated using the formula V = I × r, where 'I' is the current and 'r' is the internal resistance. Given that the current I = 4 A and the internal resistance r = 0.55 Ω, the lost voltage is 4 A × 0.55 Ω = 2.20 V.

Common mistake: Students might mistakenly divide the current by the internal resistance $(4 / 0.55 ≈ 7.27 V)$ instead of multiplying, leading them to choose an incorrect option like D.