JAMB Physics 2016 Past Questions & Answers

Myopia, also known as short-sightedness, is an eye defect where light from distant objects is focused in front of the retina, causing blurry vision. To correct this, a diverging lens is required to spread the light rays before they enter the eye's lens. A concave lens is a diverging lens, which effectively moves the focal point backward onto the retina, resulting in a clear image.

Common mistake: Students often confuse the correction for myopia with that for hyperopia (long-sightedness), which requires a converging convex lens, leading them to incorrectly choose option D.

The force on a charged particle moving in a magnetic field is given by the formula F = qvBsinθ, where θ is the angle between the velocity (v) and the magnetic field (B). When the particle moves parallel to the field, the angle θ is 0°. Since sin(0°) = 0, the force (F) on the particle is zero. According to Newton's first law, an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force, so the particle continues in a straight line.

Common mistake: Students often mistakenly choose a curved path because they remember that magnetic fields deflect charges, but they forget that this deflection force is zero when the charge's motion is parallel to the field.

Evaporation is the process where a liquid turns into a gas or vapour. The rate of this process is affected by humidity, which is the amount of water vapour in the air. When humidity is very low, the air is dry and can easily absorb more water vapour, which makes the water from the pool evaporate very quickly.

Common mistake: Students might mistakenly choose 'Temperature decreases' because they know evaporation causes cooling, but the question asks about the rate of the evaporation process itself, not its effect on temperature.

The acceleration due to gravity (g) at the Earth's surface (radius R) is given by the formula g = GM/R². For the satellite in orbit at a radius of 4R, its acceleration 'a' is given by a = GM/(4R)². When you expand the bracket, this becomes a = GM/(16R²), which is the same as $(1/16)$ * (GM/R²). Since g = GM/R², the satellite's acceleration is therefore g/16.

Common mistake: Students often mistakenly choose g/4 because they forget to square the entire distance (4R) in the denominator of the gravitational acceleration formula, leading to an incorrect inverse relationship instead of the correct inverse square relationship.

This question is about the conversion of energy from one form to another. Chemical energy is converted directly to light in things like burning candles or the bioluminescence of fireflies. Electrical energy is converted directly to light in common devices like electric bulbs and LEDs. Sound energy, however, is a form of mechanical energy and does not directly convert to light energy in a simple process.

Common mistake: Students might mistakenly choose option C, thinking that all forms of energy can be easily converted into any other form, but the direct conversion of sound to light is not a common or simple physical process.

In a pinhole camera, the magnification is the ratio of image distance to object distance. Since the image distance (the length of the camera) is fixed, the size of the image is inversely proportional to the object's distance from the pinhole. Therefore, if the object distance is reduced by half (brought closer), the image size will become double its original size.

Common mistake: Students often mistakenly choose 'Is halved' because they assume a direct relationship, forgetting that as the object gets closer to the pinhole, the light rays spread out more on the screen, creating a larger image.

Initially, the object is 15cm from the mirror, so its image is also 15cm behind the mirror. When the mirror is moved 5cm further away, the new distance from the object to the mirror becomes 15cm + 5cm = 20cm. Since it's a plane mirror, the new image will also be 20cm behind the mirror. Therefore, the total distance between the object and the new image is the object-to-mirror distance plus the mirror-to-image distance, which is 20cm + 20cm = 40cm.

Common mistake: Students might incorrectly calculate the initial object-image distance (30cm) and add the new object-mirror distance (20cm) to get 50cm, failing to understand how the image position changes relative to the mirror.

The efficiency of a machine measures how much of the work you put in (work input) is converted into useful work (work output). Friction is a force that opposes motion, and some of the work input is always used to overcome this friction, which is then lost as heat. Therefore, if friction increases, more energy is wasted, and the machine becomes less efficient.

Common mistake: Students often mistakenly choose option D, thinking that more friction means the machine is working harder, but friction actually increases the effort required, which lowers the mechanical advantage (Load/Effort).

A telescope is the correct instrument because it is specifically designed to view very distant objects, such as stars and planets. It works by using a combination of lenses or mirrors to collect and focus light from these far-off objects, making them appear larger and brighter to the observer. This allows us to see details in the night sky that are not visible with the naked eye.

Common mistake: Students might mistakenly choose a microscope because it is also a magnifying instrument, but they forget that a microscope is used for viewing very small objects up close, not distant objects like stars.

The angular magnification of a simple astronomical telescope is calculated by dividing the focal length of the objective lens $(f_o)$ by the focal length of the eyepiece lens $(f_e)$. Given that the objective focal length is 30cm and the eyepiece focal length is 3cm, the magnification is M = $f_o$ / $f_e$ = 30cm / 3cm = 10.

Common mistake: Students often make the mistake of multiplying the two focal lengths $(30 x 3 = 90)$, leading to the incorrect option D, instead of dividing them as required by the formula.

To find the decrease in length, we use the formula for linear thermal expansion: Change in Length = Original Length × Coefficient of linear expansion × Change in Temperature. First, calculate the change in temperature, which is 50°C - 10°C = 40°C. Then, multiply all the values together: 10 m × (3 x 10⁻⁵ K⁻¹) × 40 K. This gives a result of 1200 x 10⁻⁵ m, which simplifies to 1.2 x 10⁻² m.

Common mistake: A common mistake is incorrectly converting the calculated value (1200 x 10⁻⁵ m) into standard scientific notation, which can lead to choosing an answer with the wrong power of ten.

When an athlete perspires, their body releases sweat onto the skin. This sweat then turns from a liquid into a gas (water vapour) in a process called evaporation. For this change of state to happen, the sweat must absorb energy, which it takes from the athlete's body in the form of heat, thereby cooling the athlete down.

Common mistake: Students might choose other heat transfer methods like convection or radiation, but the question's key word 'perspires' specifically points to the cooling effect of evaporation.

This question is based on Newton's Law of Cooling, which states that the rate at which a body cools is directly proportional to the temperature difference between the body and its surroundings. The 'enclosure' acts as the surroundings for the heated liquid. Therefore, the temperature in the enclosure is a key factor that determines how quickly the liquid loses heat and cools down.

Common mistake: Students might mistakenly choose option D because a larger volume of liquid takes more time to cool, but the fundamental rate of cooling is driven by the temperature difference with the surroundings.

Heat capacity is the quantity of heat energy required to raise the temperature of a given mass of a substance by 1 Kelvin. The question refers to 'a mass', which means the entire body, not a specific unit of mass. Therefore, the correct answer is heat capacity, which is represented by the formula C = Q/ΔT.

Common mistake: Students often mistakenly choose 'Specific heat capacity' because they confuse it with 'Heat capacity', but 'specific' heat capacity refers to the heat needed to raise the temperature of a unit mass (1kg) of the substance.

When an object is placed between two parallel mirrors, the light rays from the object reflect back and forth between the mirrors. The image formed by the first mirror acts as an object for the second mirror, which then forms another image. This new image then acts as an object for the first mirror, and this process repeats endlessly, creating a series of images that appear to stretch into the distance. In theory, this results in an infinite number of images.

Common mistake: Students might mistakenly believe there is a practical limit to the number of reflections and choose a large but finite number, without understanding that theoretically, the process continues indefinitely.

Semiconductors are materials, like silicon, that are neither good conductors nor good insulators. At low temperatures, their electrons are mostly bound and cannot move freely to conduct electricity. When the temperature increases, the atoms vibrate more, providing enough thermal energy to break some electrons free, which can then move and carry current, thereby increasing the material's conductivity.

Common mistake: Students may mistakenly choose Current or Voltage because they are related to electricity, but the question asks about an intrinsic property of the semiconductor material itself, which is its response to heat.

The correct option is C because it makes a false statement. According to the kinetic theory of matter, the molecules and atoms that make up all substances are in a state of continuous, random motion. This motion is a form of energy, and the temperature of a substance is a measure of the average kinetic energy of its moving particles.

Common mistake: Students might mistakenly choose option A if they are unfamiliar with Brownian motion, thinking it is a complex term used in a false statement.

A dynamo is a type of electric generator that works using the principle of electromagnetic induction. When the coil inside the dynamo is rotated, which is a form of mechanical work, it cuts through a magnetic field. This action induces an electric current, thereby converting the mechanical energy of rotation into electrical energy.

Common mistake: Students often confuse a dynamo with an electric motor, which performs the opposite conversion of electrical energy into mechanical (kinetic) energy.

Saturated vapour pressure is the pressure exerted by a vapour when it is in equilibrium with its liquid. When the temperature of the liquid increases, the molecules gain more kinetic energy and more of them escape from the liquid surface to become vapour. This increase in the number of vapour molecules leads to more frequent collisions, which results in a higher saturated vapour pressure.

Common mistake: Students might mistakenly choose options related to volume, confusing this concept with gas laws like Boyle's law, but saturated vapour pressure for a given liquid depends only on its temperature.

To move the mass upwards, the applied force must do two things: overcome the downward force of gravity (its weight) and provide the additional force needed for the upward acceleration. The weight of the mass is W = mg = 60kg × 10ms⁻² = 600N. The net force needed to cause the acceleration is $F_net$ = ma = 60kg × 10ms⁻² = 600N. Therefore, the total upward force required is the sum of the weight and the net force, which is 600N + 600N = 1200N.

Common mistake: Students often mistakenly calculate only the net force needed for acceleration (F=ma=600N) or only the weight (W=mg=600N), forgetting that the total applied force must account for both.

For the ruler to be balanced, the clockwise moment about the pivot must equal the anticlockwise moment. The anticlockwise moment is created by the 10N force, calculated as 10N × 30cm = 300 Ncm. To balance this, the clockwise moment from the 15N force must also be 300 Ncm. Therefore, 15N multiplied by the unknown distance must equal 300, which means the distance is 300 / 15 = 20cm.

Common mistake: Students may mistakenly choose 30cm, thinking the distances must be equal, but they forget that it is the moments (force times distance) that must be equal, not the distances themselves.

To find the time taken to reach the maximum height in projectile motion, we use the formula t = (u sinθ) / g. Given the initial velocity (u) is 300m/s, the angle (θ) is 30°, and g is 10m/s², we substitute these values. Since sin(30°) = 0.5, the calculation is t = $(300 × 0.5)$ / 10, which simplifies to 150 / 10, giving a result of 15 seconds.

Common mistake: Students might mistakenly calculate the total time of flight (2u sinθ / g), which is 30s (Option A), instead of the time to reach only the maximum height.

This problem requires using the first equation of motion, which is v = u + at. In this question, the final velocity 'v' is 0 (because the train halts), the initial velocity 'u' is 20ms⁻¹, and the acceleration 'a' is -2ms⁻² (since it is a deceleration). By substituting these values into the formula, we get 0 = 20 + (-2)t, which simplifies to 2t = 20. Therefore, the time 't' is 20 divided by 2, which equals 10s.

Common mistake: A common mistake is to forget the correct formula and simply multiply the given numbers $(20 x 2 = 40)$, leading to the incorrect choice of 40s.

The electromagnetic spectrum arranges different types of waves in order of their wavelength. The order from the longest wavelength to the shortest is: Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, and finally Gamma rays. As Gamma rays are at the end of this list, they have the highest energy and the shortest wavelength among all the options.

Common mistake: Students sometimes confuse the relationship between wavelength and energy, and may incorrectly choose Infrared rays because they are associated with heat, without recalling that Gamma rays have the highest energy and therefore the shortest wavelength.

The relationship between half-life (T½) and the decay constant (λ) is given by the formula T½ = 0.693 / λ. In this question, the decay constant λ is given as 10⁻⁶ s⁻¹. Substituting this value into the formula gives T½ = 0.693 / 10⁻⁶ s. This simplifies to 0.693 × 10⁶ s, which in standard form is 6.93 × 10⁵ s.

Common mistake: A common mistake is to correctly calculate 0.693 × 10⁶ s but then make an error with the power of ten when converting to standard form, leading to an incorrect option like C.