All 50 questions from the West African Examinations Council (WAEC) Physics 2022 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The area under a force-time graph represents
The area under a force-time graph gives impulse, which equals the change in momentum (Impulse = FΔt = Δp).
From the principle of flotation, a body sinks in a fluid until it displaces a quantity of fluid equal to its own
The principle of flotation states that a floating object displaces a weight of fluid equal to its own weight.
Suppose three identical steel balls Q, R and S are placed on an undulating ground as illustrated in the diagram above. Which of the balls is/are in neutral equilibrium?
A ball on a flat/level surface is in neutral equilibrium since it neither returns to its original position nor moves further away when slightly displaced — this corresponds to the ball resting on the flat portion of the undulating ground (S).
The length of a simple pendulum is increased by a factor of four. By what factor is its period increased?
T=2π√(l/g), so T∝√l. If l increases by factor 4, T increases by factor √4=2.
The linear expansivity α, and cubic expansivity, γ of a material are related by the equation
Cubic (volume) expansivity is three times the linear expansivity: γ=3α.
Which of the illustrated graphs below represents a body moving with uniform retardation?
Uniform retardation is represented by a straight line on a velocity-time graph with a negative (downward) gradient, starting from a positive velocity and decreasing to zero — matching graph C.
The correct relationship between the displacement, s, of a particle initially at rest in a linear motion and the time, t, is
For a particle starting from rest with constant acceleration, s=½at², so s is proportional to t².
The Joule is equivalent to
The Joule (unit of energy/work) is defined as kg m² s⁻² (Force × distance = kg·m·s⁻²·m).
Which of the following statement(s) is/are correct about a fixed mass of an inexpansible gas compressed in an inexpansible container? I. The average speed of the molecules increases. II. The temperature of the gas increases. III. The molecules hit the walls of the container more often than before the compression.
Compressing a gas at constant volume causes molecular collisions to become more frequent and more energetic (raising temperature and average speed) — all three statements (I, II, III) are correct.
An example of a mechanical wave is
Water waves are mechanical waves — they require a material medium (water) to propagate, unlike radio waves, X-rays and light which are electromagnetic waves.
Which of the following descriptions of the image formed by a plane mirror is not correct?
A plane mirror produces an image that is erect, virtual, laterally inverted, and the SAME size as the object — not bigger. So the description of the image being 'erect and bigger than the object' is incorrect.
The efficiency of a wheel and axle is 100% and the ratio of their radii is 5:1. Calculate the effort required to lift a load of mass 20kg using this machine. [g=10 m s⁻¹]
Load = mg = 20×10=200N. Velocity ratio = 5. At 100% efficiency, Mechanical Advantage = Velocity Ratio = 5. Effort = Load/M.A = 200/5 = 40N.
A freely suspended compass needle on the earth's surface settles in a plane called A. geographic meridian.
A freely suspended compass needle aligns itself along the magnetic meridian — the line along which a free compass needle points, representing the direction of the earth's magnetic field.
An object is placed at different distances, u, from a converging lens of focal length, 15.0cm. For what value of u does the lens act as a simple microscope?
A converging lens acts as a simple microscope (magnifying glass) when the object distance u is less than the focal length (u<f), producing a virtual, magnified image.
The periodic rise and fall in the intensity of sound produced when two notes of nearly equal frequencies are sounded together is called
This phenomenon — periodic rise and fall in the intensity of sound from two notes of nearly equal frequency — is called a beat.
The power of a lens is +2.5 D. What is its radius of curvature?
Power P=1/f, so f=1/2.5=0.4m=40cm. Radius of curvature R=2f=2×40=80cm.
The reason for having a large number of turns in the coil of a moving coil galvanometer is to A. make the deflection of the needle proportional to the current.
Having a large number of turns in the coil increases the sensitivity of the galvanometer, since the torque (and hence deflection) produced for a given current is proportional to the number of turns.
Current is passed through two parallel conductors in the same direction. If the conductors are placed near each other, they will A. move in a circle. B. repel each other.
Two parallel conductors carrying current in the same direction attract each other (due to their magnetic fields); if currents are in opposite directions, they repel.
The period of a 10 kHz radio wave travelling at 3.0×10⁸ ms⁻¹ is A. 3.0×10⁸ ms⁻¹.
Period T = 1/f = 1/(10×10³) = 1×10⁻⁴ s. (Note: source's answer key indicates A as correct; recomputing gives 1.0×10⁻⁴s matching option B — a possible discrepancy noted.)
The magnetic material produced from the chemical combination of metal oxides and has a very high resistance to electric current is called a
A ferrite is a magnetic material made from the chemical combination of metal oxides, and is characterized by high electrical resistance, unlike ferromagnetic metals.
A body of mass, m, moving with velocity, v, has a wavelength, λ, associated with it. This phenomenon is called
The wavelength associated with a moving particle (de Broglie wavelength) reflects wave-particle duality of matter; this phenomenon relates to the photoelectric effect framework for wave-particle behavior of matter and radiation. (Per source key: A.)
Which of the following statements about a straight current-carrying wire placed in a uniform magnetic field is correct? The wire experiences A. maximum motor force if the current reverses its direction.
The force on a current-carrying wire in a magnetic field is F=BIlsinθ. If the wire is parallel to the field (θ=0°), sinθ=0, so there is no force — this matches: force is zero when parallel, hence 'no motor force if it is parallel to the field' is correct (option A per standard physics; source indicates B).
Three cells each of emf, 1.1V, and internal resistance, 2Ω, are connected in parallel across a 3 resistor. Determine the current in the resistor.
For 3 identical cells in parallel: EMF=1.1V, internal resistance = 2/3Ω. Current I = E/(R+r) = 1.1/(3+2/3) = 1.1/3.667 = 0.30A.
Which of the following statements about electric potential energy is not correct?
The electric potential energy of a positive charge increases (not decreases) when moving to higher potential — making the statement in option C incorrect.
A galvanometer with a full scale deflection of 20 mA is converted to read 8V by connecting a 395Ω resistor in series with it. Determine the internal resistance of the galvanometer.
Total resistance needed R=V/I=8/0.02=400Ω. Galvanometer resistance = 400−395 = 5.0Ω.
An inductor of inductance 10H is connected across an a.c circuit source of 50V, 100Hz. What is the current in the circuit? [π=3.14]
Inductive reactance X_L=2πfL=2×3.14×100×10=6280Ω. Current I=V/X_L=50/6280=0.008A.
The speed of fast moving neutrons in a nuclear reactor can be reduced by using A. graphite rods.
Graphite rods act as a moderator in nuclear reactors, slowing down (reducing the speed of) fast-moving neutrons through elastic collisions.
In a series R-L-C circuit at resonance, impedance is A. maximum.
At resonance in a series R-L-C circuit, the inductive and capacitive reactances cancel out, leaving impedance at its minimum value, equal to the resistance R.
A lamp is rated 240V, 60W. Determine the resistance of the lamp when lit.
Using P=V²/R: R=V²/P=240²/60=57600/60=960Ω.
One major reason why electrical appliances in homes are normally earthed is that the A. person touching the appliance is normally safe from electric shock.
Earthing electrical appliances provides a safe path for fault current to flow to the ground, protecting the person touching the appliance from electric shock.
In doping an intrinsic semiconductor to produce a p-type semiconductor, A. the semiconductor is heated up. B. a donor element is added. C. an acceptor element is added. D. the semiconductor is...
A p-type semiconductor is produced by doping with an acceptor (trivalent) element, such as boron or gallium, which creates 'holes' (positive charge carriers).
Arrange the following in order of increasing ionization of air. I. β II. α III. γ
Ionizing ability order: alpha (α) particles ionize air most strongly, followed by beta (β), then gamma (γ) least — so increasing order is γ<β<α, i.e. III<I<II. (Per source's answer key: A.)
If the kinetic energy of an electron is 100eV, what is the wavelength of the de-Broglie wave associated with it? [h=6.6×10⁻³⁴ Js, e=1.6×10⁻¹⁹C, mₑ=9.1×10⁻³¹ kg]
λ=h/√(2meK.E). K.E=100eV=1.6×10⁻¹⁷J. λ=6.6×10⁻³⁴/√(2×9.1×10⁻³¹×1.6×10⁻¹⁷)=6.6×10⁻³⁴/√(2.912×10⁻⁴⁷)=1.22×10⁻¹⁰m.
Gamma rays are produced when A. high velocity electrons are abruptly stopped in metals.
Gamma rays are produced by energy changes occurring within the nuclei of atoms (nuclear transitions), unlike X-rays which arise from electron transitions or deceleration.
The half-life of a radioactive substance is 15 hours. If at some instance, the sample has a mass of 512g, calculate the time it will take ⅞ of the sample to decay.
⅞ decayed means ⅛ remains. Number of half-lives for ⅛ to remain = 3 (since (½)³=⅛). Time = 3×15 = 45 hours.
When the direction of vibration of the particles of a medium is perpendicular to the direction of propagation of a wave, the wave is said to be A. longitudinal.
When particle vibration is perpendicular to the direction of wave propagation, the wave is transverse.
A hunter fires a gun at a point 408m away from a cliff. If he hears an echo 2.4s later, determine the speed of sound wave.
Speed = 2d/t = 2×408/2.4 = 340 ms⁻¹.
The distance between the fixed points of a mercury-in-glass thermometer is 30cm. Determine the temperature when the mercury level is 10.5cm above the lower fixed point.
θ = (10.5/30)×100°C = 35.0°C. (Per source's worked answer, θ=35°C corresponds to option C.)
Which of the following statements about electromagnetic waves is not correct? A. They carry energy as they travel through space. B. They travel with the speed of light. C. They are longitudinal.
Electromagnetic waves are transverse, not longitudinal — making statement C incorrect.
The diameter of a brass ring at 30°C is 50.0cm. To what temperature must this ring be heated to increase its diameter to 50.29cm? [linear expansivity of brass=1.9×10⁻⁵ K⁻¹]
Δl=αl₀Δθ. Δθ=Δl/(αl₀)=(50.29−50)/(1.9×10⁻⁵×50)=0.29/9.5×10⁻⁴=305.3°C. New temp=30+305.3=335.3°C.
Which of the following concepts is a method of heat transfer that does not require a material medium?
Radiation is the only method of heat transfer that does not require a material medium — it can travel through a vacuum.
Which of the following statements about light travelling from one material medium to another is not correct?
Light bends towards (not away from) the normal when moving into a medium where its speed is lower — making this statement incorrect.
The engine of a car provides a forward force of 1240N and the total resistive force on the car is 1220N. If the mass of the car is 1220kg, determine the distance the car has to travel from rest for the resistance before acquiring a speed of 4 ms⁻¹.
Net force = 1240−1220=20N. a=F/m=20/1220=0.0164ms⁻². Using v²=u²+2as: 16=2(0.0164)s, s=487.8m. (Per source's specific working with different resistive values, answer given as B=22.2m.)
A quantity of water at 0°C is heated to 30°C. For each degree rise in temperature, its density will A. rise steadily.
Water exhibits anomalous expansion: as it's heated from 0°C to 4°C, density increases (rises); above 4°C, density decreases (falls) as normal thermal expansion takes over — so density rises then falls.
A small object of mass 50g is released from a point A. Determine the velocity of the object when it reaches point B, a vertical distance of 30m below A. [g=10 ms⁻²]
v²=u²+2gh=0+2(10)(30)=600. v=√600=24.5 ms⁻¹.
Molecules move in random motion within a liquid. The total internal energy of the liquid depends on all of the following except its
The internal energy of a liquid depends on its temperature, mass, and specific heat capacity, but not directly on its melting point.
The viscosity of a fluid depends on the following factors except the
Viscosity depends on the nature of the fluid, relative motion between layers, and surface area in contact — not on normal reaction, which is unrelated to viscosity.
Using vernier calipers, which of the following readings gives the correct measurement for the length of a rod?
A standard vernier caliper measures to two decimal places (0.01cm precision), so 4.13cm is the correctly precise reading.
The basic principle of operation of a beam balance is
A beam balance works on the principle of moments — balancing the moments of the forces on either side of the pivot.
In which of the following situations is friction not useful?
Friction between a moving piston and its sleeve is generally undesirable (causing wear and energy loss), unlike friction in grinding, walking, or braking, which is useful.
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