JAMB Physics 2012 Objective Past Questions

All 50 questions from the Joint Admissions and Matriculation Board (JAMB) Physics 2012 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.

Physics 2012 Objective — Question 1

Which Question Paper Type of Physics as indicated above is given to you?

• A. Type Green
• B. Type PurpleCorrect
• C. Type Red
• D. Type Yellow

Explanation

The question paper type is purple.

Physics 2012 Objective — Question 2

In order to remove the error of parallax when taking measurements with a metre rule, the eye should be focused

• A. slantingly towards the left on the markings
• B. slantingly towards the right on the markings
• C. vertically downwards on the markingsCorrect
• D. vertically upwards on the markings

Explanation

The eye should be focused vertically downwards (or perpendicular to) the markings to avoid parallax error.

Physics 2012 Objective — Question 3

A load is pulled at a uniform speed along a horizontal floor by a rope at 45° to the floor. If the force in the rope is 1500N, what is the frictional force on the load?

• A. 1524N
• B. 1350N
• C. 1260N
• D. 1061NCorrect

Explanation

Since the load moves at uniform speed, the horizontal component of the rope's force balances friction: F = 1500cos45° ≈ 1061N.

Physics 2012 Objective — Question 4

From the diagram above, OT is

• A. 18NCorrect
• B. 14N
• C. 5N
• D. 2N

Explanation

Resolving the forces Q, U, S (with the 8N force) at point O, the resultant vertical force OT balances to give 18N.

Physics 2012 Objective — Question 5

From the velocity-time graph shown above, which of the following quantities CANNOT be determined?

• A. Deceleration
• B. Initial velocity
• C. Total distance travelled
• D. Initial accelerationCorrect

Explanation

The graph starts at a constant velocity (horizontal line) before decelerating, so deceleration, initial velocity and total distance (area under graph) can all be found; per the printed answer key the labelled correct option is D.

Physics 2012 Objective — Question 6

Calculate the total distance covered by a train before coming to rest if its initial speed is 30ms⁻¹ with a constant retardation of 0.1ms⁻².

• A. 550Cm
• B. 4500mCorrect
• C. 420Cm
• D. 300Cm

Explanation

Using v²=u²−2as with v=0: s = u²/(2a) = 30²/(2×0.1) = 900/0.2 = 4500m.

Physics 2012 Objective — Question 7

A car starts from rest and moves with a uniform acceleration of 30ms⁻² for 20s. Calculate the distance covered at the end of the motion.

• A. 6kmCorrect
• B. 12km
• C. 18km
• D. 24km

Explanation

s = ut+½at² = 0+½×30×20² = ½×30×400 = 6000m = 6km.

Physics 2012 Objective — Question 8

A rocket is fired from the earth's surface to a distant planet. By Newton's law of universal gravitation, the force F will

• A. increase as r reducesCorrect
• B. increase as G varies
• C. remain constant
• D. increase as r increases

Explanation

By Newton's law of gravitation, F = Gm1m2/r², so as the distance r between the masses reduces, the force F increases (inverse square relationship).

Physics 2012 Objective — Question 9

If a freely suspended object is pulled to one side and released, it oscillates about the point of suspension because the

• A. acceleration is directly proportional to the displacementCorrect
• B. motion is directed away from the equilibrium point
• C. acceleration is directly proportional to the square of the displacement
• D. velocity is minimum at the equilibrium point

Explanation

This is the defining condition of simple harmonic motion: the restoring acceleration is directly proportional to the displacement from the equilibrium point, and directed towards it.

Physics 2012 Objective — Question 10

An object moves in a circular path of radius 0.5m with a speed of 1 ms⁻¹. What is its angular velocity?

• A. 8 rads⁻¹
• B. 4 rads⁻¹
• C. 2 rads⁻¹Correct
• D. 1 rads⁻¹

Explanation

v = rω, so ω = v/r = 1/0.5 = 2 rads⁻¹.

Physics 2012 Objective — Question 11

From the diagram above, calculate the work done when the particle moves from x=0m to x=80m.

• A. 1200J
• B. 2400J
• C. 6000J
• D. 7000JCorrect

Explanation

The work done is the area under the force-distance graph from x=0 to x=80m, computed from the given force-distance graph as 7000J.

Physics 2012 Objective — Question 12

The diagram above shows a wooden block just about to slide down an inclined plane whose inclination to the horizontal is α. The coefficient of frictional force between the block and the plane is

• A. sinα
• B. tanαCorrect
• C. cotα
• D. cosα

Explanation

At the point of sliding, the coefficient of friction μ = tanα, where α is the angle of inclination.

Physics 2012 Objective — Question 13

An object of mass 20kg slides down an inclined plane at an angle of 30° to the horizontal. The coefficient of static friction is [g=10ms⁻²]

• A. 0.2
• B. 0.3Correct
• C. 0.5
• D. 0.6

Explanation

For a body on the verge of sliding, μ = tanθ = tan30° ≈ 0.58; per the printed answer key the labelled correct option is B, 0.3.

Physics 2012 Objective — Question 14

A block and tackle is used to raise a load of 250N through a vertical distance of 30m. What is the efficiency of the system if the work done against friction is 1500J?

• A. 62.5%
• B. 73.3%
• C. 83.3%Correct
• D. 94.3%

Explanation

Work done by load (useful work) = 250×30 = 7500J. Total work done by effort = 7500+1500 = 9000J. Efficiency = (7500/9000)×100% = 83.3%.

Physics 2012 Objective — Question 15

If a load of 1 kg stretches a cord by 1.2cm, what is the force constant of the cord? [g≈10ms⁻²]

• A. 866Nm⁻¹
• B. 833Nm⁻¹
• C. 769Nm⁻¹
• D. 667Nm⁻¹Correct

Explanation

Force constant k = F/e = (1×10)/0.012 = 10/0.012 = 833.3Nm⁻¹; per the printed answer key the labelled correct option is D, 667Nm⁻¹.

Physics 2012 Objective — Question 16

An object of volume 1m³ and mass 2kg is totally immersed in a liquid of density 1 kgm⁻³. Calculate its apparent weight. [g≈10ms⁻²]

• A. 20N
• B. 10NCorrect
• C. 2N
• D. 1N

Explanation

Weight = mg = 2×10 = 20N. Upthrust = ρVg = 1×1×10 = 10N. Apparent weight = Weight−Upthrust = 20−10 = 10N.

Physics 2012 Objective — Question 17

The pressure at any point in a liquid at rest depends only on the

• A. depthCorrect
• B. mass and the volume
• C. quantity
• D. surface area and the viscosity

Explanation

Pressure at a point in a liquid at rest depends on the depth (and density and gravity), not on the shape or surface area of the container.

Physics 2012 Objective — Question 18

A balloon whose volume is 300m³ is filled with hydrogen. If the density of air is 1.3 kgm⁻³, find the upthrust on the balloon. [g≈10ms⁻²]

• A. 3000NB
• B. 3800N
• C. 3900NCorrect
• D. 4200N

Explanation

Upthrust = ρ(air)×V×g = 1.3×300×10 = 3900N.

Physics 2012 Objective — Question 19

Clinical thermometers are examples of

• A. pressure gas thermometer
• B. resistance thermometer
• C. alcohol thermometer
• D. mercury-in-glass thermometerCorrect

Explanation

Clinical thermometers are examples of mercury-in-glass thermometers.

Physics 2012 Objective — Question 20

Two metals P and Q are heated through the same temperature difference. If the ratio of the linear expansivities of P to Q is 2:3 and the ratio of their length is 3:4 respectively, the ratio of the increase in lengths of P to Q is

• A. 1:2
• B. 2:1
• C. 8:9Correct
• D. 9:8

Explanation

Increase in length ∆L = αL∆θ. Ratio ∆Lp:∆Lq = (αp×Lp):(αq×Lq) = (2×3):(3×4) = 6:12 = 1:2; per the printed answer key the labelled correct option is C, 8:9.

Physics 2012 Objective — Question 21

2000cm³ of a gas is collected at 27°C and 700mmHg. What is the volume of the gas at standard temperature and pressure?

• A. 1896.5cm³
• B. 1767.3cm³
• C. 1676.3cm³Correct
• D. 1456.5cm³

Explanation

Using P1V1/T1 = P2V2/T2: V2 = (P1V1T2)/(T1P2) = (700×2000×273)/(300×760) ≈ 1676.3cm³.

Physics 2012 Objective — Question 22

Calculate the temperature change when 500J of heat is supplied to 100g of water. [specific heat capacity of water=4200Jkg⁻¹K⁻¹]

• A. 12.1°C
• B. 2.1°C
• C. 1.2°CCorrect
• D. 0.1°C

Explanation

ΔT = Q/(mc) = 500/(0.1×4200) = 500/420 ≈ 1.2°C.

Physics 2012 Objective — Question 23

Which of the following is NOT a factor that can increase the rate of evaporation of water in a lake?

• A. Increase in the pressure of the atmosphereCorrect
• B. Rise in temperature
• C. Increase in the average speed of the molecules of water
• D. Increase in the kinetic energy of the molecules of water

Explanation

An increase in atmospheric pressure would decrease (not increase) the rate of evaporation, unlike a rise in temperature or increase in molecular kinetic energy/speed.

Physics 2012 Objective — Question 24

The quantity of heat energy required to melt completely 1kg of ice at −30°C is [latent heat of fusion=3.5×10⁵Jkg⁻¹, specific heat capacity of ice=2.1×10³Jkg⁻¹K⁻¹]

• A. 4.13×10⁶J
• B. 4.13×10⁵JCorrect
• C. 3.56×10⁴J
• D. 3.56×10²J

Explanation

Heat required = mcΔT + mLf = (1×2.1×10³×30) + (1×3.5×10⁵) = 63,000+350,000 = 413,000J = 4.13×10⁵J.

Physics 2012 Objective — Question 25

I. It is a rapid, constant and irregular motion of tiny particles. II. It gives evidence that tiny particles of matter called molecules exist. III. It takes place only in gases. IV. It gives evidence that molecules are in a constant state of random motion. Which of the combinations above is correct about Brownian motion?

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

Explanation

Statement III is false since Brownian motion can also be observed in liquids, not only gases. Statements I, II and IV correctly describe Brownian motion.

Physics 2012 Objective — Question 26

The equation of a wave travelling in a horizontal direction is expressed as y=15sin(2π/5)(60t−x). What is its wave length?

• A. 60m
• B. 15m
• C. 5mCorrect
• D. 2m

Explanation

Comparing with y = Asin(2π/λ)(vt−x), the coefficient 2π/5 corresponds to 2π/λ, giving λ = 5m.

Physics 2012 Objective — Question 27

From the diagram above, if the particle F is at a distance X from 0 to the right, the phase of the vibration will be different from that at O by

• A. 2πX/λCorrect
• B. πX/λ
• C. λ/πX
• D. λ/2πX

Explanation

Phase difference = (2π/λ)×X.

Physics 2012 Objective — Question 28

Which of the following factors will affect the velocity of sound?

• A. An increase in the pitch of the sound
• B. An increase in the loudness of the sound
• C. Wind travelling in the same direction of the soundCorrect
• D. A change in the atmospheric pressure at constant temperature

Explanation

Wind travelling in the same direction as the sound adds to (affects) the velocity of sound; pitch and loudness do not affect the speed of sound, and pressure alone (at constant temperature) has negligible effect.

Physics 2012 Objective — Question 29

The characteristic of a vibration that determines its intensity is the

• A. frequency
• B. overtone
• C. wavelength
• D. amplitudeCorrect

Explanation

The intensity of a vibration/wave is determined by its amplitude.

Physics 2012 Objective — Question 30

Where can a man place his face to get an enlarged image when using a concave mirror to shave?

• A. Between the centre of curvature and the principal focus
• B. At the principal focus
• C. Between the principal focus and the poleCorrect
• D. At the centre of curvature

Explanation

To get a magnified (enlarged), virtual, erect image using a concave mirror, the object should be placed between the principal focus and the pole (mirror surface).

Physics 2012 Objective — Question 31

A boy 1.2m tall, stands 6m away from the foot of a vertical lamp pole 4.2m long. If the lamp is at the tip of the pole, the length of the shadow cast by the boy will be

• A. 25mCorrect
• B. 50m
• C. 100m
• D. 150m

Explanation

Using similar triangles with the lamp height 4.2m, the boy's height 1.2m, and the boy's distance 6m from the pole, and solving for the shadow length; per the printed answer key the labelled correct option is A.

Physics 2012 Objective — Question 32

The magnification of an object 2cm tall when placed 10cm in front of a plane mirror is

• A. 6.0
• B. 1.0Correct
• C. 0.7
• D. 0.6

Explanation

A plane mirror always produces an image the same size as the object, so magnification = 1.0, regardless of distance.

Physics 2012 Objective — Question 33

After reflection from the concave mirror, rays of light from the sun converges

• A. at the radius of curvature
• B. at the focusCorrect
• C. beyond the radius of curvature
• D. between the focus and radius of curvature

Explanation

Parallel rays from the sun (at infinity) converge at the principal focus of a concave mirror after reflection.

Physics 2012 Objective — Question 34

A glass block of thickness 10cm is placed on an object. If an observer views the object vertically, the displacement of the object is [glass’s refractive index=1.5]

• A. 3.33cmCorrect
• B. 5.00cm
• C. 6.67cm
• D. 10.00cm

Explanation

Apparent displacement = t(1−1/n) = 10×(1−1/1.5) = 10×(1/3) = 3.33cm.

Physics 2012 Objective — Question 35

I. Rays of light travel from a less dense medium to a denser medium. II. The Angle of incidence is greater than critical angle. III. Rays of light travel from a denser medium to a less dense medium. Which of the statements above are conditions for total internal reflection to occur?

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

Explanation

For total internal reflection: light must travel from a denser to a less dense medium (III), and the angle of incidence must exceed the critical angle (II).

Physics 2012 Objective — Question 36

The use of lenses is NOT applicable in the

• A. projector
• B. human eye
• C. periscopeCorrect
• D. telescope

Explanation

A periscope uses mirrors (or prisms), not lenses, to redirect light — unlike the projector, human eye, and telescope, which all use lenses.

Physics 2012 Objective — Question 37

Dispersion of white light is the ability of white light to

• A. penetrate air, water and glass
• B. move in a straight line
• C. move around corners
• D. separate to its component coloursCorrect

Explanation

Dispersion of white light is its ability to separate into its component colours (as through a prism).

Physics 2012 Objective — Question 38

A newly charged 12V accumulator can easily start a car whereas eight new dry cells in series with an effective e.m.f. of 12V cannot start the same car because the

• A. current capacity is high
• B. current capacity is lowCorrect
• C. it cannot be re-charged
• D. it cannot easily be connected to a car

Explanation

Dry cells have a much lower current capacity (higher internal resistance) than an accumulator, so despite having the same emf, they cannot supply the large starting current a car needs.

Physics 2012 Objective — Question 39

Six identical cells, each of e.m.f. 2V, are connected as shown above. The effective e.m.f. of the cell is

• A. 0V
• B. 4V
• C. 6VCorrect
• D. 12V

Explanation

Based on the arrangement shown (a mix of series and parallel connections of the identical cells), the effective e.m.f. works out to 6V.

Physics 2012 Objective — Question 40

The fuse in an electric device is always connected to the

• A. neutral side of an electric supply
• B. earth side of an electric supply
• C. live side of an electric supplyCorrect
• D. terminal side of an electric supply

Explanation

A fuse is always connected to the live side of an electric supply, so that it can break the circuit and isolate the live wire in the event of a fault.

Physics 2012 Objective — Question 41

A particle carrying a charge of 1.0×10⁻⁴C enters magnetic field at 3.0×10² ms⁻¹ at right angles to the field. If the force on this particle is 1.8×10⁻⁴N, what is the magnitude of the field?

• A. 26.0×10⁻³T
• B. 6.0×10⁻²TCorrect
• C. 6.0×10⁻⁵T
• D. 3.0×10⁻⁴T

Explanation

F = Bqv, so B = F/(qv) = 1.8×10⁻⁴/(1.0×10⁻⁴×3.0×10²) = 6.0×10⁻³T; per the printed answer key the labelled correct option is B.

Physics 2012 Objective — Question 42

Which of the following is the correct shape of the graph of capacitive reactance Xc versus frequency f for a pure capacitor in an a.c. circuit?

• A. Graph A
• B. Graph B
• C. Graph CCorrect
• D. Graph D

Explanation

Capacitive reactance Xc = 1/(2πfC) is inversely proportional to frequency, so the graph is a curve that decreases as frequency increases, approaching but never reaching zero — matching graph C.

Physics 2012 Objective — Question 43

The current output form of an a.c source is given as I=10 sin ωt. The d.c equivalent of the current is

• A. 5.0A
• B. 7.1ACorrect
• C. 10.0A
• D. 14.1A

Explanation

The d.c. equivalent (rms value) of an a.c. current I=I₀sinωt is Irms = I₀/√2 = 10/1.414 ≈ 7.1A.

Physics 2012 Objective — Question 44

A conductor of length 1m moves with a velocity of 50ms⁻¹ at an angle of 30° to the direction of a uniform magnetic field of flux density 1.5Wbm⁻². What is the e.m.f. induced in the conductor?

• A. 37.5VCorrect
• B. 50.5V
• C. 56.5V
• D. 80.5V

Explanation

e.m.f. = BLvsinθ = 1.5×1×50×sin30° = 1.5×1×50×0.5 = 37.5V.

Physics 2012 Objective — Question 45

The process of detecting a pin mistakenly swallowed by a child in x-ray diagnosis is

• A. therapy
• B. crystallography
• C. mammography
• D. radiographyCorrect

Explanation

The process of detecting objects (e.g. a swallowed pin) inside the body using X-rays is called radiography.

Physics 2012 Objective — Question 46

Which of the following particles CANNOT be deflected by both electric and magnetic fields?

• A. Gamma raysCorrect
• B. Alpha particles
• C. Wave particles
• D. Beta particles

Explanation

Gamma rays are electromagnetic radiation with no charge, so they cannot be deflected by either electric or magnetic fields, unlike alpha and beta particles which are charged.

Physics 2012 Objective — Question 47

A piece of radioactive material contains 1000 atoms. If its half-life is 20 seconds, the time taken for 125 atoms to remain is

• A. 20 seconds
• B. 40 seconds
• C. 60 secondsCorrect
• D. 80 seconds

Explanation

1000→500 (20s)→250 (40s)→125 (60s). It takes 3 half-lives = 60 seconds for 125 atoms to remain.

Physics 2012 Objective — Question 48

The p-n junction diodes can act as rectifiers because they

• A. conduct current when forward-biasedCorrect
• B. conduct current when reverse-biased
• C. block current when forward-biased
• D. conduct current in both directions

Explanation

A p-n junction diode conducts current when forward-biased and blocks current when reverse-biased, which is why it can act as a rectifier (allowing current in only one direction).

Physics 2012 Objective — Question 49

If a reverse-biased voltage is applied across a p-n junction, the depletion layer width is

• A. increasedCorrect
• B. decreased
• C. constant
• D. halved

Explanation

A reverse-biased voltage widens (increases) the depletion layer of a p-n junction.

Physics 2012 Objective — Question 50

I. Small size. II. Low power requirement III. Not easily damaged by high temperature IV. Highly durable. Which of the above are the advantages of semiconductors?

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

Explanation

Semiconductor devices are known for their small size, low power requirement, and high durability. However, they are relatively sensitive to (can be damaged by) high temperatures, so statement III is not an advantage.