WAEC Physics 2024
Questions & Answers

Students might mistakenly choose option A or C by reversing the specific roles played by the different parts of the container. The vacuum space acts as an absolute barrier that eliminates the medium required for conduction and convection, completely halting those two transfer methods. Meanwhile, the silvered inner and outer surfaces tackle thermal radiation by reflecting radiant heat back into the flask. Common mistake: Mixing up which structural feature prevents conduction/convection versus which addresses radiation.

Students might mistakenly select option A by confusing velocity-time graphs with displacement-time graphs, where the gradient represents velocity rather than acceleration. Acceleration is formally defined as the rate of change of velocity over time, which corresponds geometrically to the gradient or slope of a velocity-time graph. Common mistake: Confusing the slope of a displacement-time graph (velocity) with the slope of a velocity-time graph (acceleration).

Students might choose option A, C, or D by underestimating the effect that surface area has on pressure distribution. Since pressure is calculated as force divided by area, and the downward force exerted by body weight remains constant across all options, standing on a single foot halves the contact surface area, thereby maximizing the resulting pressure. Common mistake: Forgetting that reducing the contact area while keeping weight constant significantly increases pressure.

Students might mistakenly select option B, C, or D by confusing cathode rays with subatomic particles derived from nuclear reactions or channel rays. Cathode rays are specifically generated inside a vacuum tube under high voltage and consist of a high-speed stream of electrons emitted from the cathode. Common mistake: Confusing cathode rays (electrons) with anode rays or protons.

Students might mistakenly pick option C by assuming that inserting an insulating material somehow hinders charge storage. Capacitance is directly enhanced when a dielectric material is placed between the conducting plates because it increases the capacitance value by a factor greater than one, following the relationship C = epsilon naught A over d scaled by the dielectric constant. Common mistake: Believing that adding a dielectric material decreases or has no effect on a capacitor's storage capacity.

Students might mistakenly select option A or B by assuming that wave frequency changes when light transitions between optical mediums. When a light ray enters a denser medium from a less dense medium, its speed decreases because the refractive index increases (v = c/n). However, the frequency remains entirely unaltered because frequency is an intrinsic characteristic determined solely by the wave source. Common mistake: Assuming that changes in light speed through a medium also cause a shift in its frequency.

Students might choose option B or D by confusing circuit safety devices with voltage regulators or power-saving appliances. A fuse is specifically designed as a thin sacrificial wire that melts and interrupts the electrical path whenever current surges past a designated threshold, protecting the wider circuit from overloads. Common mistake: Assuming a fuse regulates or reduces normal operating current to save energy.

Students might mistakenly select option A or B by assuming that movement requires an unbalanced forward or backward force. According to Newton's first law of motion, a body maintains a constant, uniform velocity whenever the net resultant force acting upon it equals zero, meaning opposing forces like friction are perfectly balanced. Common mistake: Believing that a net forward force is required to keep an object moving at a steady velocity.

Students might mistakenly select option B, C, or D by assuming that mass fluctuations or external forces do not disrupt momentum conservation. For the law of conservation of momentum to hold true, the system must be completely isolated so that no external forces act upon it, and it must be closed so that no mass enters or leaves the system. Common mistake: Overlooking the requirement that system mass must remain constant alongside zero external forces.

Students might mistakenly choose option B by calculating the centrifugal force component alone and forgetting to add the weight vector. At the bottom of a vertical circular path, the string must support both the downward weight of the stone (mg) and provide the upward centripetal force (mv squared over r). Substituting the mass of 0.2kg, speed of 5ms⁻¹, radius of 1.5m, and gravity of 10ms⁻² gives 3.33N for the centripetal component and 2.0N for the weight, resulting in a total tension of 5.33N. Common mistake: Omitting the weight of the object when calculating tension at the lowest point of a vertical loop.

Students might mistakenly choose option A or B by confusing ammeter conversion with voltmeter modifications. To convert a milli-ammeter into an ammeter capable of handling higher currents, a low-value shunt resistor must be connected in parallel with the device to divert excess current safely away from the sensitive meter movement. Common mistake: Placing the shunt resistor in series instead of parallel when converting a meter range.

Students might mistakenly select option B by reading only the distance from the object to the mirror rather than calculating the total span requested. In a plane mirror, the virtual image forms directly behind the glass at a distance equal to the object distance (1.5m), meaning the total separation distance between the object and its image is 1.5m plus 1.5m, totaling 3.0m. Common mistake: Reporting the distance from the mirror to the image instead of the total distance between the object and the image.

Students might mistakenly select option B or D by choosing aperture stops or single lens adjustments that fail to address dispersion across wavelengths. Chromatic aberration occurs because different colors refract at varying focal lengths, which is successfully corrected by pairing a converging crown glass lens with a diverging flint glass lens in an achromatic doublet. Common mistake: Trying to fix chromatic dispersion using single lenses or rim covers instead of a combined lens system.

Students might select option B or C by miscalculating the ratio of submerged length to total height. The density of the floating wood relative to water equals the fraction of its submerged volume to total volume, which is calculated as 4.5cm submerged divided by the 10.0cm total side length, yielding 0.45gcm⁻³ when multiplied by the water density of 1gcm⁻³. Common mistake: Multiplying or dividing incorrect dimension ratios when applying the floatation density formula.

A student might incorrectly choose options like 108°F by forgetting to add the 32 offset after scaling. To determine the correct temperature, multiply the Celsius value 60 by 9/5 (or 1.8) to get 108, then add 32 to arrive at 140°F. Common mistake: forgetting to include the final addition of 32 in the conversion formula.

Options such as dental operation or detecting fracture in bones might look plausible because x-rays are famously utilized in medical imaging and therapy. However, finding the depth of a mine relies instead on seismic surveys. Common mistake: confusing medical and geological survey techniques.

A student might mistakenly select 2.25 × 10¹N or other values by miscalculating exponents during division. By applying Coulomb's law where force equals k times the square of the charge divided by the square of the distance, substituting 9 × 10⁹ for k, 1.0 × 10⁻⁶C for the charges, and 2.0 × 10⁻¹m for the separation gives 9 × 10⁻³ divided by 0.04, yielding 2.25 × 10⁻¹N. Common mistake: mishandling decimal placement when squaring the distance.

One might mistakenly pick 6.25 × 10⁻¹⁴N by mistakenly dividing instead of multiplying the given values. Centripetal force is calculated as mass multiplied by radial acceleration, so taking 3.6 × 10⁻⁶kg and multiplying by 4.3 × 10⁷ms⁻² results in 1.548 × 10²N, which rounds to 1.55 × 10²N. Common mistake: performing division of mass and acceleration instead of multiplication.

Distractors like twice the focal length might seem correct because a real image can be formed at 2f, but that describes the object position rather than the total object-screen separation. A convex lens forms a real image with a minimum object-to-screen distance of 4f, which occurs precisely when the object is placed at 2f and its image is formed at 2f. Common mistake: confusing the object-to-lens distance with the total object-to-screen distance.

Options such as 1.0 × 10⁻¹⁸J might tempt a student who accidentally subtracts incorrectly or misinterprets the exponents. Maximum kinetic energy of the ejected electrons is found by subtracting the threshold energy 6.6 × 10⁻¹⁹J from the incident energy 1.1 × 10⁻¹⁸J (expressed as 11 × 10⁻¹⁹J), giving 4.4 × 10⁻¹⁹J, which approximates to 4.5 × 10⁻¹⁹J. Common mistake: failing to align the powers of ten before performing subtraction.