All 40 questions from the Joint Admissions and Matriculation Board (JAMB) Physics 2023 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A string of length 1.4 m is extended by 0.04 m when a load of 0.8 kg is suspended. How far will it extend if a force of 32 N is applied? (g=10 m/s², elastic limit not exceeded)
k=8N/0.04m=200 Nm⁻¹; e=32/200=0.16 m.
From the circuit diagram, calculate the energy stored in the capacitor.
E=½CV²=½×14×10⁻⁶×50²=1.75×10⁻² J.
A car accelerates uniformly from rest at 3 ms⁻². Its velocity after travelling 32.67 m:
v²=2×3×32.67=196 → v=14 m/s.
An object of mass 10 kg is released from 5 m height. KE just before hitting the ground:
KE=mgh=10×10×5=500 J.
A body projected vertically upward at 5 m/s from 1.4 m above ground. Total time to reach ground:
Time up=0.5 s, H=1.25 m; total down from top=2.65 m; t₂=0.728 s; total=1.228 s.
A device that converts mechanical energy into electrical energy is:
A dynamo (generator) converts mechanical to electrical energy.
A car travelling at 50 m/s overcomes frictional resistance of 100 N. Power developed: (1hp=0.75KW)
P=Fv=100×50=5000 W=5 kW; in hp=5/0.75≈6.7 hp.
The quality of a note depends on its:
Quality (timbre) depends on the overtones present.
Which relation about focal lengths of objective and eyepiece of a compound microscope is correct?
In compound microscope, objective has shorter focal length than eyepiece.
The functional difference between a lens and a mirror: a lens:
Lens refracts; mirror reflects.
Which type(s) of motion do the wheels of a moving car undergo?
Wheels both spin (rotational) and move forward (translational).
The temperature at which water vapour is just sufficient to saturate the air is the:
Dew point is where air becomes saturated with water vapour.
What is the best method of demagnetizing a steel bar magnet?
The electrical (solenoid AC) method is most effective for demagnetisation.
The magnitude of the angle of dip at the equator is:
At the equator, Earth's field is horizontal; angle of dip=0°.
The diagram illustrates an EM wave travelling at 3×10⁸ m/s. Calculate the frequency of the wave.
3 wavelengths span 0.6 m → λ=0.2 m; f=3×10⁸/0.2=1.5×10⁹ Hz.
An object is placed between two plane mirrors inclined at 45°. How many images formed?
N=360°/45°-1=7 images.
A milliammeter can be converted to a voltmeter by using a:
A high resistance (multiplier) in series converts it to a voltmeter.
A 15μF capacitor is connected to 240 V, 50 Hz AC. Reactance of the capacitance:
Xc=1/(2πfC)=1/(2π×50×15×10⁻⁶)≈212 Ω.
An object weighs 15 kg in air and 11 kg in a liquid. Upthrust exerted by the liquid:
Upthrust=loss in weight=(15-11)×10=40 N.
A machine lifts 20 N load through 10 m. Efficiency 40%. Work input:
Output=200 J; input=200/0.4=500 J.
Which waves do NOT need a material medium for propagation except:
Sound is mechanical and needs a medium; the others do not.
Which is a property of steel?
Steel is a hard magnetic material suitable for permanent magnets.
Cost of electricity is #5 per kWh. Cost of running a 250 V, 4 A appliance for 3 hours:
P=1000 W=1 kW; E=3 kWh; cost=#15.
An image in a convex lens is upright and magnified 3×. Focal length=15 cm. Object distance:
m=3 (virtual); v=-3u; 1/15=1/u-1/3u=2/3u → u=10 cm.
The property of a fluid used to determine suitability as a lubricant is its:
Viscosity measures resistance to flow; higher viscosity = better lubricant.
A 120 g mass is placed at the 10 cm mark on a uniform metre rule making it balance horizontally on a fulcrum at 35 cm. Mass of the rule:
Moments: 120×25=m×15 → m=200 g.
A stone is pushed horizontally at 15 m/s from a table 1.5 m high. Distance from foot of table to impact:
t=√(2×1.5/10)=0.5477 s; R=15×0.5477≈8.22 m.
Wheel radius 30 cm, axle radius 6 cm. Effort to lift 120 N load (100% efficiency):
MA=R/r=30/6=5; Effort=120/5=24 N.
A hypsometer is used for determining:
Hypsometer measures the boiling point of water (steam point) to find altitude.
5Ω and 10Ω resistors in series then parallel with 24 V. Ratio of power (series:parallel):
P_series=38.4 W; P_parallel=172.8 W; ratio=38.4:172.8=2:9.
Iron weighs 125 N in air, 100 N in liquid of density 1000 kgm⁻³. Volume of iron:
U=25 N; V=U/(ρg)=25/10000=2.5×10⁻³ m³.
Object placed between principal focus and optical centre of convex lens can be used as:
Object inside focal length → magnifying glass (simple microscope).
Which motion has constant speed but is still accelerating?
Uniform circular motion: constant speed, changing direction → centripetal acceleration.
Which is NOT a direct consequence of rectilinear propagation of light?
Diffraction results from wave nature of light, not rectilinear propagation.
A rectangular prism of thickness d, refractive index n. Apparent upward displacement of object below:
Displacement=d-d/n=d(n-1)/n.
At low humidity, the human skin is usually:
Low humidity causes dry, rough skin.
Radius of earth is 6400 km. Escape velocity of a satellite:
v=√(2gR)=√(1.28×10⁸)≈11313 ms⁻¹≈1.13×10⁴ ms⁻¹.
The correct unit of energy density is:
Energy density=J/m³=kgm²s⁻²/m³=kgm⁻¹s⁻².
Wavelength of first overtone of note in closed pipe of length 33 cm:
First overtone in closed pipe: L=3λ/4 → λ=4L/3=44 cm.
A force changes momentum of body from 12 kgms⁻¹ to 16 kgms⁻¹ in 0.2 s. Magnitude of impulse:
Impulse=Δp=16-12=4 Ns.
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