All 50 questions from the West African Examinations Council (WAEC) Physics 2023 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
Advertisement
The instrument used to measure relative humidity is a
A hygrometer is the instrument used to measure relative humidity. (Barometer measures atmospheric pressure; hydrometer measures relative density of liquids; manometer measures fluid pressure.)
Which part of the human eye performs the same function as the diaphragm in a lens camera?
The iris in a lens camera controls the amount of light that gets through to the lens; it performs the same function as the diaphragm of the human eye.
An electron moves from an energy level of -8.6 eV to another level of -3.5 eV. Determine the frequency of the absorbed radiation. [1eV=1.6×10⁻¹⁹J, h=6.6×10⁻³⁴Js]
ΔE = E₂-E₁ = -3.5eV-(-8.6eV) = 5.1eV = 8.16×10⁻¹⁹J. f = ΔE/h = 8.16×10⁻¹⁹/6.6×10⁻³⁴ = 1.24×10¹⁵ Hz.
A ball of mass 0.8 kg is dropped from a height, H. Just before hitting the ground, its velocity is 5.0 ms⁻¹. Determine H. [g=10 ms⁻²]
Using v²=u²+2gH: 25=0+2(10)H → H=25/20=1.25m.
Which of the following statements about latent heat are correct? I. When ice melts, latent heat is absorbed II. When water freezes, latent heat is given off III. When water evaporates, latent heat is absorbed IV. When water vapour condenses, latent heat is absorbed
Latent heat is absorbed when ice melts (I), given off when water freezes (II), and absorbed when water evaporates (III). Statement IV is incorrect since condensation releases (not absorbs) latent heat, so I, II and III only are correct.
Increasing the frequency of a sound wave produces a sound with
The pitch of a sound wave depends on the frequency of vibration; sound waves with higher frequency produce higher-pitched notes.
Which of the following diagrams correctly illustrates the mode of oscillation in a tube for the first overtone?
The first overtone in a tube (closed at one end) corresponds to the third harmonic pattern with the correct number of nodes and antinodes, matching option B.
In a mass spectrometer, an ion of charge q, and mass, m, moving in a path of radius, r, in a field of flux density, B, has a speed of
The magnetic force provides centripetal force: Bqv=mv²/r → v=Bqr/m.
A sound of frequency 512 Hz reaches a listener 100 m away. If the sound travels in air at s.t.p, what is its wavelength? [speed of sound in air = 331 ms⁻¹]
λ = v/f = 331/512 = 0.646 m.
In the Rutherford scattering experiment, a beam of alpha particles was fired at a thin gold film and few of the particles were deflected considerably. This shows that the nucleus of an atom
The deflection of alpha particles shows that the nucleus of the atom is positively charged and is concentrated in a very tiny volume.
A charge of 10 C is transferred across a potential difference of 220 V. Determine the work done.
W = qV = 10×220 = 2200 J.
A solenoid is constructed by winding an insulated copper on a long test tube. A constant direct current is passed through the solenoid. Which of the following actions will not increase the strength of the magnetic field of the solenoid?
Nickel, soft iron and steel are ferromagnetic materials that would increase the magnetic field strength; brass is non-ferromagnetic and would not increase the field.
The following statements are advantages of a solid dielectric material between the plates of a capacitor except that it
A solid dielectric increases the electrical resistance/insulation of the capacitor, not its electrical conduction; it does not conduct electricity between the plates.
Which of the following statements about a ferromagnetic material is correct?
Ferromagnetism is the property of a material to be strongly attracted to a magnetic field and to become a powerful magnet; ferromagnetic materials have a high and positive magnetic susceptibility.
A ball, P, is released from the roof of a building at the same time as another ball, Q, is thrown vertically upward from the base of the building. Which of the following statements is correct?
Both balls are in free fall/motion under gravity, so both experience the same acceleration due to gravity (g), acting downward — the same direction.
A planet has mass, M, and radius R. If the universal gravitational constant is G, what is the expression for the escape velocity of an object on the planet?
Escape velocity vₑ = √(2GM/R).
The specific latent heat of vapourization of lead is 8.7×10⁵ Jkg⁻¹. This means that 8.7×10⁵ J of thermal energy is required to change
Specific latent heat of vaporization is the heat required to convert 1 kg of a substance (already molten/liquid) to vapour at constant temperature and pressure.
A 100 kg device is pulled up a plane inclined at 30° to the horizontal with a force of 1000 N. If the coefficient of friction between the device and the surface is 0.25, determine the total force opposing the motion. [g=10 ms⁻²]
Total opposing force = μmgcosθ + mgsinθ = 0.25×100×10×cos30° + 100×10×sin30° = 216.5+500 = 716.5 N.
Two objects, A and B, accelerate from rest at uniform rates. B accelerates twice as much as A. Compared to A, B travels
Since both start from rest, distance ∝ acceleration (for the same time). If B's acceleration is twice A's, B travels twice as far as A.
The diagram illustrates a hot metal suspended at the centre of a closed uniform box. Thermometers E, F, G and H are placed in contact with four sides of the box. Which of the four thermometers would register the highest temperature?
Since the hot metal is suspended at the centre of the box, all four thermometers (E, F, G, H) — being equidistant from the metal — will record an equal amount of temperature.
A liquid is left in an open dish. After several days, there is less liquid in the dish. Which of the following statements explains this observation?
The most energetic molecules of the liquid are able to leave the surface and escape into the air (evaporation), which is why the liquid level reduces over several days.
The colours of the visible light region of the electromagnetic spectrum that have the shortest and longest wavelengths respectively are
In the visible spectrum, violet has the shortest wavelength (highest frequency) and red has the longest wavelength (lowest frequency).
Which of the following equations is not a correct mirror formula? [The symbols have their usual meanings]
f=1/D is not a correct mirror formula — D is not a standard mirror-formula symbol; the correct relation is f=D (focal length formula uses different variables).
An atom in an excited state is one whose
When an atom is exposed to heat, light or other forms of energy, its electrons absorb the energy and move to a higher energy level/orbital; the atom in this state is said to be excited.
The conclusive test for magnetism in a steel bar suspended horizontally at its midpoint is when the bar
The conclusive test for magnetism is repulsion, since a magnet always attracts unmagnetized ferromagnetic materials, but only repels another magnet — repulsion alone proves the bar is a magnet.
Which of the following devices is used to compare the relative magnitudes of charges on two given bodies?
A gold leaf electroscope is used to compare the relative magnitudes of charges on two given bodies, since the divergence of its leaves is proportional to the amount of charge.
A direct current cannot pass through a parallel plate capacitor because
Direct current cannot pass through a parallel plate capacitor because the dielectric (insulator) between the plates is non-conducting.
The process of producing electric current by a changing magnetic field is referred to as
Electromagnetic induction is the process of producing electric current by a changing magnetic field.
The sagging of overhead electrical wires is caused by
Other consequences of linear/thermal expansion include buckling of railway lines, cracking of glass tumblers due to excessive heating, and sagging of telephone/overhead cables.
A cell of emf 2 V has an internal resistance of 0.5 Ω. A current of 0.4 A passes through an external resistor, P. Determine the resistance of P.
Using I=E/(R+r): 0.4=2/(R+0.5) → (R+0.5)×0.4=2 → R+0.5=5 → R=4.5 Ω.
The property of a body that determines the direction of heat flow when the body is in contact with another body is
The direction of heat flow is from a hotter region to a colder region — determined by the temperature of the bodies.
In an RLC series circuit at resonance, the voltages across the resistor and the inductor are 30 V and 40 V respectively. Determine the voltage across the capacitor.
At resonance, XL=XC, so VL=VC. Since VL=40V, VC=40V also.
The purpose of commutators in a direct current motor is to
The purpose of commutators in a DC motor is to reverse the direction of the current after every half rotation.
A lead bullet of mass 0.05 kg is fired with a speed of 200 ms⁻¹ into a lead block of mass 0.95 kg at rest. Given that the lead block moves after the impact, determine its kinetic energy.
By conservation of linear momentum: v=(0.05×200)/(0.05+0.95)=10/1=10 ms⁻¹. KE of the block after collision = ½×0.95×10² = 47.5 J, closest to option A (50 J).
What is the name given to the force of attraction between the nucleons in the nucleus of an atom?
Nuclear force is the force that acts between the protons and neutrons (nucleons) of atoms, binding the nucleons into atomic nuclei.
In a controlled thermal fission reactor, a nuclide, the use of control rods will not affect the
Control rods (e.g. boron rods) accelerate, slow down or shut down the nuclear reaction and ensure it takes place at the right speed; they do not directly affect the amount of radiation produced.
The most appropriate value of fuse for a kettle rated 220 V, 1.06 kW is
I=P/V=1060/220=4.82A. A slightly higher standard fuse rating is chosen, i.e. 5 A.
The type of mirror used by dentists to inspect the teeth of patients is a
Dentists use concave mirrors to inspect teeth because a concave mirror forms a virtual, erect and enlarged image when the object is placed within its focus.
Determine the wavelength of the waves shown in the diagram (using the diagram to answer questions 39 and 40).
From the diagram, l=n(λ/2)=5(λ/2); given l=125cm and n=5 loops, λ=2l/5=2(125)/5=50cm=0.5m.
Determine the frequency of the waves.
Using v=fλ: f=v/λ=120/0.5=240 Hz.
Which of the following statements about the properties of the electric field produced by charged parallel plates is not correct?
The electric field has the same strength (uniform) at each point in the electric field, regardless of position near or away from the edges — the field strength does NOT depend on position, making statement C the incorrect one.
A car, P, with a velocity of 30 ms⁻¹ is travelling in the same direction as a car, Q, with a velocity of 20 ms⁻¹. The velocity of P relative to Q is
Relative velocity of P with respect to Q = Vp - Vq = 30-20 = 10 ms⁻¹.
The range of wavelengths of the infra-red waves in an electromagnetic spectrum is 10⁻³ m to 10⁻⁶ m. Which of the following statements about the wavelength of the radiation is not correct? The wavelength is
Since infrared waves range from 10⁻³m to 10⁻⁶m, stating the wavelength is shorter than 10⁻⁶m is incorrect since the range extends only up to that value, not below it.
When an electron jumps directly from an orbit of n=4 to n=2,
When an electron jumps directly from a higher energy level (n=4) to a lower energy level (n=2), it undergoes a transition accompanied by the emission of a photon with energy equal to the difference between the two orbits.
When a light-weight body and a massive body are acted upon by the same force for the same period of time, the
Since both bodies are acted on by the same force for the same time, the change in momentum experienced by both bodies is the same (Newton's second law); hence momenta of both bodies remain the same.
Which of the following devices is associated with alternating currents only?
A step-up transformer works only with alternating current (AC), since transformers rely on a changing magnetic flux which only AC can provide.
A body starts with an initial velocity of 20 ms⁻¹ and moves with a uniform acceleration, a, for 15 seconds. Which of the following equations represents the distance, S, travelled?
Using s=ut+½at²: s=20(15)+½a(15)² = 300 + 225a/2.
The ratio of maximum range to maximum height of a projectile is 4. Determine the angle of projection.
Given Rmax:Hmax=4, using Rmax=u²/g and Hmax=u²sin²θ/2g, solving gives sin²θ=1/2, so θ=sin⁻¹(√2/2)=45°, a value between the given options C and D.
The following statements are observations made about a towing vehicle and a bus being towed. I. The force exerted on the bus by the towing vehicle is of the same magnitude as the force that the bus exerts on the road. II. The force exerted on the bus by the towing vehicle is of the same magnitude as the force exerted on the towing vehicle by the bus. III. The towing vehicle exerts a force on the bus greater than the force exerted by the bus on the towing vehicle. IV. The towing vehicle exerts a force on the bus that is the same as the force the road exerts on the towing vehicle. Which of the following statements is/are correct?
By Newton's third law of motion, the force exerted on the bus by the towing vehicle is equal in magnitude and opposite in direction to the force exerted on the towing vehicle by the bus — so only statement II is correct.
The diagram illustrates a velocity-time graph. Determine the distance between X and Y.
Distance = area of the rectangle formed = L×B = (8-4)×40 = 4×40 = 160.0 m.
Advertisement
…and/or go further with premium services and No Ads.