WAEC Physics 2018 Objective Past Questions

All 50 questions from the West African Examinations Council (WAEC) Physics 2018 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.

Physics 2018 Objective — Question 1

The S.I. Unit of sound energy is

• A. Hz
• B. cb
• C. db
• D. JCorrect

Explanation

Sound energy is a form of energy, so like all forms of energy it is measured in Joules (J).

Physics 2018 Objective — Question 2

The general definition of elastic modulus is

• A. stress/strainCorrect
• B. strain/stress
• C. stress×strain
• D. √stress×strain

Explanation

Elastic (Young's) modulus is defined as the ratio of stress to strain.

Physics 2018 Objective — Question 3

The diagram above illustrates a simple barometer. Which distance measures the atmospheric pressure?

• A. PQ
• B. QRCorrect
• C. RS
• D. QS

Explanation

Atmospheric pressure is balanced by the height of the mercury column, i.e. the vertical distance between the top of the mercury in the tube and the mercury surface in the open reservoir (QR).

Physics 2018 Objective — Question 4

The property of a body to remain at rest or to continue in a uniform motion in a straight line is called

• A. momentum
• B. inertiaCorrect
• C. impulse
• D. energy

Explanation

This resistance to a change in state of motion is the definition of inertia.

Physics 2018 Objective — Question 5

During a training session, two footballers pass a ball repeatedly between each other. The to and fro motion of the ball is not simple harmonic because I. acceleration of the ball is not directed towards a fixed point II. restoring force is not directed towards the centre III. acceleration of the ball is not directly proportional to the displacement from a fixed point. Which of the statements above are correct?

• A. I and III only
• B. I and II only
• C. II and III only
• D. I, II and IIICorrect

Explanation

All three conditions required for SHM (fixed centre, restoring force towards centre, acceleration proportional to displacement) are violated for the ball's motion, so I, II and III are all correct.

Physics 2018 Objective — Question 6

A dam is able to hold a large quantity of water because its wall is

• A. thickest at the top
• B. thickest at the middle
• C. thickest at the bottomCorrect
• D. of the same thickness throughout

Explanation

Water (hydrostatic) pressure increases with depth, so the dam wall must be thickest at the bottom to withstand the greatest pressure.

Physics 2018 Objective — Question 7

A body of mass m moving round a circle of radius r with a uniform speed v experiences a centripetal force F. The work done by the centripetal force on it is

• A. Fv
• B. zeroCorrect
• C. Fmr
• D. Frlm

Explanation

The centripetal force is always directed perpendicular to the velocity (towards the centre), so it does no work on the body.

Physics 2018 Objective — Question 8

A block is acted upon by two horizontal forces as illustrated in the diagram above. The block accelerated at 1.5ms⁻². Calculate the mass of the block

• A. 6kgCorrect
• B. 9kg
• C. 10kg
• D. 15kg

Explanation

Net force = 10N − 1N = 9N. Mass = F/a = 9/1.5 = 6kg.

Physics 2018 Objective — Question 9

Which of the following quantities are dimensionally independent (dimensionless)? I. dielectric constant II. Momentum constant III. Efficiency IV. Refractive index

• A. I and II
• B. I, II, III and IVCorrect
• C. II, III and IV
• D. I, III and IV

Explanation

Dielectric constant, momentum constant, efficiency and refractive index are all expressed as ratios of like quantities, so all four are dimensionless.

Physics 2018 Objective — Question 10

A body is projected with an initial velocity 'u' at an angle to the horizontal. If Rmax is the maximum range of the projectile, what does u²/Rmax represent?

• A. the vertical distance covered
• B. acceleration due to gravityCorrect
• C. the horizontal distance covered
• D. the acceleration of the body

Explanation

At maximum range (θ=45°), Rmax = u²/g, so u²/Rmax = g, the acceleration due to gravity.

Physics 2018 Objective — Question 11

An object at rest is said to possess

• A. potential energyCorrect
• B. kinetic energy
• C. chemical energy
• D. electrical energy

Explanation

A body at rest, by virtue of its position, possesses potential energy.

Physics 2018 Objective — Question 12

According to Newton's law of cooling, the heat energy lost per unit area of a body depends on the I. Surface area II. Nature of the surface III. Temperature of the surface IV. Excess temperature over the surroundings

• A. I and II only
• B. II and IV onlyCorrect
• C. I, II and III
• D. I, III and IV

Explanation

Since the loss is already expressed per unit area, surface area (I) is not an independent factor; the rate depends on the nature of the surface (II) and the excess temperature over the surroundings (IV).

Physics 2018 Objective — Question 13

The graph of density against temperature for water is correctly illustrated by

• A. Graph A
• B. Graph BCorrect
• C. Graph C
• D. Graph D

Explanation

Water shows anomalous expansion: its density rises to a maximum at 4°C then falls as temperature increases further, giving a peaked curve.

Physics 2018 Objective — Question 14

A football is kicked at an angle of 45° to the horizontal over a defence line with a velocity of 15ms⁻¹. Calculate the magnitude of horizontal velocity of the ball at its highest point.

• A. 0.0ms⁻¹
• B. 5.6ms⁻¹
• C. 10.6ms⁻¹Correct
• D. 15.0ms⁻¹

Explanation

The horizontal component of velocity stays constant throughout the flight: 15cos45° ≈ 10.6ms⁻¹.

Physics 2018 Objective — Question 15

The ice point on the absolute scale of temperature is

• A. 0K
• B. 32K
• C. 100K
• D. 273KCorrect

Explanation

0°C (the ice point) corresponds to 273K on the absolute (Kelvin) scale.

Physics 2018 Objective — Question 16

Which of the following factors does not increase the rate of evaporation of water in a lake?

• A. Increase in the pressure of the atmosphereCorrect
• B. Rise in the temperature
• C. Increase in the surface area of the lake
• D. Decrease in the speed of wind

Explanation

A rise in atmospheric pressure suppresses evaporation rather than increasing it; the other options all increase evaporation.

Physics 2018 Objective — Question 17

The bob of a simple pendulum takes 8.0s to complete 10 oscillations. Determine the frequency of oscillation of the bob

• A. 0.80Hz
• B. 1.25HzCorrect
• C. 7.50Hz
• D. 8.00Hz

Explanation

Frequency = number of oscillations/time = 10/8.0 = 1.25Hz.

Physics 2018 Objective — Question 18

The diagram illustrates the mercury-in-glass thermometer used for determining the temperature of a room. Use the data on it to determine the room temperature

• A. 3.3°C
• B. 7.00°C
• C. 13.00°C
• D. 30.00°CCorrect

Explanation

The 3cm mark corresponds proportionally to (3/10)×100°C = 30°C on the 0–100°C, 10cm scale.

Physics 2018 Objective — Question 19

Frequency is measured in

• A. metre per second
• B. second
• C. hertzCorrect
• D. farad

Explanation

The SI unit of frequency is the hertz (Hz).

Physics 2018 Objective — Question 20

Which of the following electromagnetic waves is most energetic?

• A. Radio waves
• B. X-rays
• C. Gamma raysCorrect
• D. Ultra-violet rays

Explanation

Gamma rays have the shortest wavelength and highest frequency of the options, so they carry the most energy (E=hf).

Physics 2018 Objective — Question 21

Rainbow formation is a natural phenomenon illustrating that white light

• A. Splits into three components after rainfall
• B. is dispersed by glass prisms
• C. Splits into its constituent colour before rainfall
• D. Is dispersed into its constituent colours by raindropsCorrect

Explanation

Raindrops act like tiny prisms, refracting and dispersing white sunlight into its constituent colours to form a rainbow.

Physics 2018 Objective — Question 22

The lens illustrated above can best be described as a

• A. converging meniscusCorrect
• B. plano-convex
• C. diverging meniscus
• D. bio-convex

Explanation

A meniscus lens (concave on one side, convex on the other) which is thicker at the centre than the edges acts as a converging lens.

Physics 2018 Objective — Question 23

Two plane mirrors are inclined to each other such that an object placed between them has 11 images. Determine the angle of inclination

• A. 30°Correct
• B. 45°
• C. 60°
• D. 90°

Explanation

Number of images n = (360/θ)−1. Setting 11=(360/θ)−1 gives θ=360/12=30°.

Physics 2018 Objective — Question 24

The pitch of a note is not affected by

• A. frequency
• B. tension in a vibrating string
• C. mass of a vibrating string
• D. amplitude of sound waveCorrect

Explanation

Pitch depends on frequency (which itself depends on the string's tension and mass per unit length); amplitude affects only loudness, not pitch.

Physics 2018 Objective — Question 25

When two flat plate conductors are arranged in such a way that they possess equal and opposite charges separated by a dielectric, they form a/an

• A. electroscope
• B. electrophorus
• C. capacitorCorrect
• D. cell

Explanation

This is the standard construction of a parallel-plate capacitor.

Physics 2018 Objective — Question 26

Which electrical device does the diagram above illustrate?

• A. a.c. generatorCorrect
• B. a.c. motor
• C. d.c. generator
• D. d.c. motor

Explanation

A coil rotating in a magnetic field connected to the external circuit via slip rings is the construction of an a.c. generator.

Physics 2018 Objective — Question 27

A simple barometer is constructed using a liquid Q, of density 16.2g/cm³. Calculate the least length of the tube to be used to measure a pressure of 1.5 atmospheres. (Density of mercury = 13.6g/cm³, 1 atmosphere = 76.0cm of mercury)

• A. 1358mm
• B. 957mmCorrect
• C. 760mm
• D. 638mm

Explanation

Equivalent mercury height = 1.5×76 = 114cm. Using ρ_Hg h_Hg = ρ_Q h_Q: h_Q = (13.6×114)/16.2 ≈ 95.7cm = 957mm.

Physics 2018 Objective — Question 28

A bar AB is balanced horizontally on two knife edges as illustrated above (F₁=20N, F₂=20N). Determine the weight of the bar

• A. 10.0N
• B. 20.0N
• C. 40.0NCorrect
• D. 50.0N

Explanation

For equilibrium, the sum of the upward reaction forces equals the weight: W = F₁+F₂ = 20+20 = 40.0N.

Physics 2018 Objective — Question 29

To obtain a virtual, erect and magnified image from a thin converging lens, an object must be placed

• A. between the focus and the lensCorrect
• B. at the focus
• C. between the focus and twice the focal length
• D. beyond twice the focal length

Explanation

Placing the object between the lens and its principal focus produces a virtual, erect, magnified image (as in a magnifying glass).

Physics 2018 Objective — Question 30

The diagram above represents a transverse travelling wave. Which two points are 180° out of phase?

• A. A and ECorrect
• B. B and D
• C. C and F
• D. D and H

Explanation

Points separated by half a wavelength are 180° out of phase; on the diagram this corresponds to points A and E.

Physics 2018 Objective — Question 31

Two objects P and Q of masses 100kg and 20kg respectively are 1.2m apart on a horizontal surface. Calculate the net gravitational force acting on Q. (G = 6.67×10⁻¹¹Nm²kg⁻²)

• A. 1.11×10⁻⁷N towards P
• B. 1.11×10⁻⁷N towards Q
• C. 9.26×10⁻⁸N towards PCorrect
• D. 9.26×10⁻⁸N towards Q

Explanation

F = Gm₁m₂/r² = (6.67×10⁻¹¹×100×20)/1.2² = 9.26×10⁻⁸N, directed towards P (the larger mass, by mutual attraction).

Physics 2018 Objective — Question 32

The primary of a transformer has 100 turns and its secondary has 200 turns. If the voltage at the primary is 100V, determine the voltage at the secondary

• A. 50V
• B. 100V
• C. 200VCorrect
• D. 400V

Explanation

Vs/Vp = Ns/Np → Vs = 100×(200/100) = 200V.

Physics 2018 Objective — Question 33

In the diagram illustrated above, a block of mass M is at rest on a plane inclined at angle θ to the horizontal. As θ increases, the velocity ratio of the plane

• A. increases
• B. decreasesCorrect
• C. remains the same
• D. decreases and later increases

Explanation

Velocity ratio of an inclined plane = 1/sinθ. As θ increases, sinθ increases, so the velocity ratio decreases.

Physics 2018 Objective — Question 34

When the speed of a car is halved, its kinetic energy is

• A. doubled
• B. quarteredCorrect
• C. halved
• D. quadrupled

Explanation

K.E. ∝ v². Halving v reduces K.E. to (½)² = ¼ of its original value — i.e. quartered.

Physics 2018 Objective — Question 35

A wire of length 400cm is stretched between two fixed points. When plucked, its fundamental frequency is 150Hz. Calculate the speed of the wave produced.

• A. 250ms⁻¹
• B. 625ms⁻¹
• C. 1200ms⁻¹Correct
• D. 1500ms⁻¹

Explanation

For a string fixed at both ends, wavelength of the fundamental λ = 2L = 8m. Speed v = fλ = 150×8 = 1200ms⁻¹.

Physics 2018 Objective — Question 36

The diagram above illustrates a wavefront. Determine the number of wavelengths in it.

• A. 4
• B. 3½Correct
• C. 2½
• D. 2

Explanation

Counting the wave crests shown along the wavefront diagram gives 3½ wavelengths.

Physics 2018 Objective — Question 37

A resistor with a fixed resistance value is called a

• A. resistance box
• B. standard resistorCorrect
• C. shunt
• D. multiplier

Explanation

A resistor manufactured to have one fixed, unchanging resistance value is called a standard resistor.

Physics 2018 Objective — Question 38

Which of the following statements is not an advantage of an alkaline accumulator?

• A. the electrolyte does not need attention
• B. it can be recharged
• C. it has low internal resistanceCorrect
• D. it has a much longer life than lead-acid accumulator

Explanation

Alkaline accumulators actually have a relatively high internal resistance compared to lead-acid accumulators, so low internal resistance is not one of their advantages.

Physics 2018 Objective — Question 39

The diagram above illustrates the wire connections to a three-pin plug. The wires P, Q and R respectively are

• A. live, neutral and earth
• B. neutral, earth and live
• C. earth, live and neutral
• D. earth, neutral and liveCorrect

Explanation

By the standard colour/position convention shown in the diagram, P, Q and R correspond to earth, neutral and live respectively.

Physics 2018 Objective — Question 40

Which of the following statements about parallel plate capacitors is/are correct? I. Capacitance of the capacitor is inversely proportional to the distance between the plates II. Capacitors can filter a.c. signals from d.c. III. Capacitors can store charges

• A. I only
• B. I and II only
• C. II and III only
• D. I, II and IIICorrect

Explanation

C=εA/d (inversely proportional to plate separation — I true); capacitors block d.c. while passing a.c., acting as filters (II true); and storing charge is a capacitor's basic function (III true).

Physics 2018 Objective — Question 41

Which of the following statements about magnetic lines of force is not correct?

• A. They pass through non-magnetic materials
• B. They run from the north pole to the south pole
• C. They are in a state of tension and tend to be shorted
• D. They intersect one anotherCorrect

Explanation

Magnetic field lines never cross or intersect one another; where lines appear to meet, the resultant field is drawn instead.

Physics 2018 Objective — Question 42

A circuit contains three ammeters A₁, A₂ and A₃ with readings of A₂ and A₃ as indicated in the diagram above. Determine the reading of A₁

• A. 2A
• B. 3ACorrect
• C. 65A
• D. 8A

Explanation

Since current from the positive terminal splits and recombines, A₁ = A₃−A₂ = 5A−2A = 3A.

Physics 2018 Objective — Question 43

In which of the following activities is an induction coil not useful?

• A. Investigation of high voltages
• B. Study of electric discharge
• C. Operation of X-ray tubes
• D. A.C. power transmissionCorrect

Explanation

Induction coils are used to generate high voltages for sparks, discharge tubes and X-ray tubes, but power transmission uses transformers, not induction coils.

Physics 2018 Objective — Question 44

In a series R.L.C. circuit, R = 10Ω, Xc = 4Ω and XL = 9Ω. The impedance of the circuit is

• A. 4.1
• B. 5.0
• C. 10.8
• D. 11.2Correct

Explanation

Z = √[R²+(XL−Xc)²] = √[10²+5²] = √125 ≈ 11.2Ω.

Physics 2018 Objective — Question 45

A student uses two compass needles to investigate the magnetic field around a bar magnet. Which of the following diagrams shows the correct directions of the needles?

• A. Diagram A
• B. Diagram BCorrect
• C. Diagram C
• D. Diagram D

Explanation

The compass needles should align tangentially along the field lines, pointing from the north to the south pole of the bar magnet, as shown in the correct diagram option.

Physics 2018 Objective — Question 46

Which of the following particles may be emitted in a process of natural radioactivity?

• A. α-particles and β-particlesCorrect
• B. α-particles and X-rays
• C. β-particles and X-rays
• D. γ-particles and X-rays

Explanation

Natural radioactive decay emits alpha, beta and gamma radiation; X-rays are not a product of nuclear decay.

Physics 2018 Objective — Question 47

In which of the following situations is the photoelectric effect employed? I. Automatic devices for switching on light at dusk II. Automatic doors in departmental stores III. Automatic devices for switching on air conditions IV. Automatic voltage stabilization

• A. I and II onlyCorrect
• B. II and IV only
• C. III and IV only
• D. I and IV only

Explanation

Light-sensitive switching (dusk sensors) and light-beam-triggered automatic doors both rely directly on the photoelectric effect; air-conditioning and voltage stabilisation do not.

Physics 2018 Objective — Question 48

Which of the following radiations has the longest wavelength?

• A. Gamma ray
• B. Radio waveCorrect
• C. Infrared ray
• D. X-ray

Explanation

Radio waves have the longest wavelength in the electromagnetic spectrum among the options given.

Physics 2018 Objective — Question 49

In which of the following fields is radioisotopes not used?

• A. Medicine
• B. Oil industry
• C. Agriculture
• D. Weather forecastCorrect

Explanation

Radioisotopes are used in medicine (diagnosis/therapy), the oil industry (tracing), and agriculture (pest control, tracers), but not in weather forecasting.

Physics 2018 Objective — Question 50

A nuclide is represented by ⁷⁰₃₂X. Determine its neutron-proton ratio

• A. 0.5
• B. 0.8
• C. 1.2Correct
• D. 1.5

Explanation

Number of neutrons = 70−32 = 38. Neutron-to-proton ratio = 38/32 = 1.2.