Physics 2021 JAMB CBT Questions

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1. A man walks 1km due east and then 1 km due north His displacement

A. √2km N 45°E
B. 1km N 30°E
C. 1km N 15°E
D. √2km N 60°E Correct Answer: Option A

2. The density of 400cm of palm oil was 0.9gcm-3 before frying. If the density of the oil was 0.6gm-3 after frying, assuming no loss of oil due to spilling, its new volume was?

A. 1360cm


B. 600cm
C. 240cm
D. 8000m



Correct Answer: Option B

Explanation
⇒
without any loss in the frying process, we have




3. Natural radioactivity consists of the emission of


A. α- particles and β-rays
B. α- particles and X-rays
C. α- particles, β - rays and g-rays
D. γ- rays and X-rays Correct Answer: Option C

4.Which of the following is true of an electrical charge?

A. Positive charge means deficit electrons
B. Negative charge means excess of electrons
C. electric current means movement of electrons
D. All of the above Correct Answer: Option D


5. Which of the following does NOT describe the Image formed by a plane minor?


A. Erect
B. Laterally inverted
C. Same distance from mirror as object
D. Magnified

Correct Answer: Option D

Explanation The image formed by a plane mirror is always virtual (the light rays do not actually come from the image), upright, and of the same shape and size as the object it is reflecting.






6


What is the resultant resistance of the circuit in the image shown?

A. 8Ω
B. 11Ω
C. 4Ω
D. 3.6Ω Correct Answer: Option A


7. Which of the following best describes the energy changes which take place when a steam engine drives a generator which lights a lamp?

A. heat ----> Light----> Sound ----> Kinetic
B. Kinetic ----> Light ----> Heat ----> Electricity
C. heat ----> Kinetic ----> Electricity ----> Heat and Light
D. electricity ----> Kinetic ----> Heat ----> Light


Correct Answer: Option C


8. Cathode rays are

A. High-energy electromagnetic waves
B. protons
C. neutrons
D. streams of electrons Correct Answer: Option D


9. A narrow beam of white light can be split up into different Colours by a glass prism. The correct explanation is that

A. white light Is an electromagnetic wave
B. the prism has all the colours of the white light
C. different colours of white light travel with different speeds in glass
D. white light has undergone total Internal reflection in the prism

Correct Answer: Option C

10


The diagram shown represents a block-and-tackle pulley system on which an effort of W Newtons supports a load of 120.0N. If the efficiency of the machine is 40, then the value of W is?
A. 28.0
B. 48.0N
C. 233.0N
D. 50.0N Correct Answer: Option D

11. What type of reaction is represented by the following scheme?




+ -----> + + energy
A. fusion reaction
B. fission reaction
C. Chain reaction
D. radioactive decay Correct Answer: Option A


12. The amount of heat needed to raise the temperature of 10kg of Copper by 1K is its

A. specific heat capacity
B. latent heat
C. heat capacity
D. internal energy Correct Answer: Option C



13. The electrochemical equivalent of silver is 0.0012g/C. If 36.0g of silver is to be deposited by electrolysis on a surface by passing a steady current for 5mins, the current must be?


A. 6000A
B. 100A
C. 10A
D. 1A Correct Answer: Option B


14. Shadows and eclipses result from the

A. refraction of light
B. reflection of light
C. defraction of light
D. rectilinear propagation of light Correct Answer: Option D



15.Which of the following obeys Ohm's law?


A. all metals
B. diode only
C. all electrolytes
D. glass Correct Answer: Option A



16. Which of the following statements are TRUE of isotopes?

I. Isotopes of an element have the same chemical properties because they have the same number of electrons
II. Isotopes of elements are normally separated using physical properties
III. Isotopes of an element have the same number of protons in their nuclei
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
17


In the diagram given the hanging mass m2 is adjusted until m1 is on the verge of sliding. The coefficient of static
A.

B.
C.
D.


Correct Answer: Option D

18. Which of the following may be used to explain a mirage?


I. Layers of air near the road surface have varying refractive indices in hot weather
II. Road surfaces sometimes become good reflectors in hot weather
III. Light from the sky can be reflected upwards after coming close to the road surface.
A. I and III only
B. II and III only
C. II only
D. I, II and III Correct Answer: Option A

19



In the diagram given if the atmospheric pressure is 760mm, the pressure in the chamber G Is
A. 660mm
B. 890mm
C. 690mm
D. 860mm Correct Answer: Option B



20. Which of the following has the lowest internal resistance when new?


A. Leclanche cell
B. Daniell cell
C. Torch battery
D. Accumulator Correct Answer: Option D

21.The pitch of an acoustic device can be increased by




A. decreasing the loudness
B. increasing the intensity
C. increasing the frequency
D. decreasing the intensity Correct Answer: Option C


22. One of the features of the fission process is that

A. it leads to chain reaction
B. its products are not radioactive
C. neutrons are not released
D. the of the masses of the reactants equals the sum of the masses of the products Correct Answer: Option A


23. The linear expansivity of brass is 2 x 10−5 C−1. If the volume of a piece of brass is 15.00cm at 0°C, what is the volume at 100°C
A. 16.03cm3
B. 15.09cm3
C. 16.00cm3
D. 15.03cm3
Correct Answer: Option B
Explanation Volume Expansivity
=




=

24.A lead bullet of mass 0.05 kg is fired with a velocity of 200 ms into a lead block of mass 0.95 kg. Given that the lead block can move freely. the final kinetic energy after impact is

A. 100J
A. 150J
C. 50J
D. 200J Correct Answer: Option C



25. In a series R-L-C circuit at resonance, the voltages across the resistor and the inductor are 30V and 40V respectively. What is the voltage across the capacitor?
A. 30V
B. 70V
C. 50V
D. 40V Correct Answer: Option D

26. If the fraction of the atoms of a radioactive material left after 120years is
, what is the half-life of the material?
A. 20 years
B. 10 years
C. 2 years
D. 24 years Correct Answer: Option A


27


In the diagram shown, which of the simple pendulum will resonate with P when set into oscillation?
A. U
B. T
C. R and T
D. Q and R
Correct Answer: Option B 28.The time rate of loss of heat by a body is proportional to the


A. temperature of its surroundings
B. temperature of the body
C. difference in temperature between the body and its surroundings
D. ratio of the temperature of the body to that of its surroundings Correct Answer: Option C


29.A positively charged rod X is brought near an uncharged metal sphere Y and is then touched by a finger with X still in place. When the finger is removed, the result is that Y has

A. no charge and a zero potential
B. a positive charge and a zero potential
C. a negative charge and a positive potential
D. a negative charge and a negative potential Correct Answer: Option D



30. Electrical appliances in homes are normally earthed so that


A. a person touching the appliances is safe from electric shock
B. both the a.c. and d.c. sources can be used
C. the appliances are maintained at a higher pd than the earth
D. the appliances are maintained at a lower pd than the earth Correct Answer: Option D

31. Gamma rays are produced when




A. high velocity electrons are abruptly stopped in metals
B. energy changes occur within the nucleus of atoms
C. energy changes occur within the electronic structure of atoms
D. electrons are deflected in very strong magnetic fields Correct Answer: Option B


32.What is the speed of a particle of mass 10-27kg whose wavelength is 10-8m.


[h = 6.63 x 10-34Js]
A. 6.63ms-1
B. 66.30ms-1
C. 663.00ms-1
D. 6630.00ms-1

Correct Answer: Option B

Explanation Energy of a particle is given by
E = hf = hV/λ (since V = fxλ)
But in terms of mass M, E = ∆MV2
∴ ∆MV2 = hV/λ
∆MV = h/λ
∴ V = h/λ∆M
V = 6.63 x 10-34/(10-27 x 10-8)
V = 6.63 x 10-34/10-35
V = 6.63 x 10-34+35
V = 6.63 x 10
V = 66.3ms-1

33.in a series R-L-C circuit at resonance, the voltages across the resistor and the inductor are 30V and 40V respectively, what is the voltage across the capacitor?
A. 30V
B. 40V
C. 50V
D. 70V
Correct Answer: Option B
Explanation At resonance, inductive reactant XL is equal to the capacitive reactance XC
i.e. XL = XC
and XL = VL/IL
and XC = VC/IC

Again since the components are in series, the same current flows in the series arrangment
i.e. IL = IC
at resonance, VL/IL = VC/IC
∴ VL = VC
= 40V

34.In the Rutherford scattering experiment, a beam of alpha particles was fired at a thin gold film with some of the particles being considerably deflected. This shows that

A. a gold nucleus contains protons, neutrons and electrons uniformly distributed in a tiny volume
B. the gold nucleus is positively charged and is concentrated in a tiny volume
C. the gold nucleus emitted alpha particles
D. the gold nucleus is concentrated in a tiny volume and contains alpha particles
Correct Answer: Option B



35 2311Na + Proton → pqX + alpha particle
What are the values of p and q respectively in the equation above?
A. 10 and 20
B. 12 and 24
C. 20 and 10
D. 24 and 12

Correct Answer: Option C
Explanation 2311Na + Proton → pqX + alpha particle
Represent;
2311Na + 11P → pqX + 42He

Thus from the above equations, p = 20 and q = 10



36. A semiconductor diode is used in rectifying alternating current into direct current mainly because it




A. allows current to flow in either direction
B. is non-linear
C. offers a high input resistance
D. allows current to flow only in one direction Correct Answer: Option D

Explanation A rectifier of an alternating current is a device which allows the flow of current only in one direction

37.if ∆x is the uncertainty in the measurement of the position of a particle along the x-axis and ∆Px is the uncertainty in the measurement of the linear momentum along the x-axis, then the uncertainty principle relation is given as

A. ∆x ∆Px ≥ h
B. ∆x ∆Px = 0
C. ∆x ∆Px < h
D. ∆x ∆Px = ∞ Correct Answer: Option A



38.When a ship sails from salt water into fresh water, the fraction of its volume above the water surface will
A. increase
B. decrease
C. remain the same
D. increase then decrease Correct Answer: Option B

Explanation Fresh water is less dense than the salt water, hence when the ship sails in fresh water, it will sink more, thus the fraction of the ship above the water surface will decrease.

39

I. Its velocity is constant
II. No work is done on the body
III. It has constant acceleration directed away from the centre
IV. The centripetal force is directed towards the centre

Which combination of the above is true of a body moving with constant speed in a circular track?
A. II and IV
B. I and IV
C. II and III
D. I and III Correct Answer: Option A



40.The velocity ratio of a machine is 5 and its efficiency is 75%. What effort would be needed to lift a load of 150N with the machine?
A. 20N
B. 30N
C. 40N
D. 50N Correct Answer: Option C

Explanation Efficiency = M.A/V.R
75% = M.A/V.R
75/100 = M.A/5
M.A = 75(5)/100 = 3.75

But M.A = Load/Effort
3.75 = 150/Effort
Effort = 150/3.75
Effort = 40N


41. The energy needed to move a unit positive charge around a complete electric circuit is called the

A. electromotive force
B. electric potential difference
C. electric energy
D. kinetic energy

Correct Answer: Option B

Explanation Electric potential difference: work needed per unit of charge to move a test charge between the two points.
Electric energy: energy derived from electric potential energy.
Kinetic energy: moving energy



42. The inner diameter of a small test tube can be measured accurately using a

A. Micrometres screw gauge
B. Pair of dividers
C. Metre rule
D. Pair of vernier calliper

Correct Answer: Option D
Explanation A vernier scale is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation; thereby increasing resolution and reducing measurement



43.A pulley system has three pulleys in the fixed block and two in the movable block and if the pulley has an efficiency of 72%, the mechanical advantage of the system is?
A. 36.0
B. 7.2
C. 5.0
D. 3.6

Correct Answer: Option D
Explanation Mechanical Advantage = V.R × Efficiency
= 5 × 0.72
= 3.6


44.When an atom loses or gain a charge it becomes

A. An electron
B. An ion
C. A neutron
D. A proton

Correct Answer: Option B
Explanation If an atom gains or loses an electron, it becomes an ion. An atom that gains a negative electron, it becomes a negative ion. If it loses an electron it becomes a positive ion



45.A ball of mass 800g moving horizontally with a speed of 5m/s hits a vertical wall and rebounds with the same speed. The impulse experienced by the ball is?
A. 0kgm
B. 2kgm/s
C. 4kgm/s
D. 8kgm/s Correct Answer: Option D

Explanation Initial momentum = (0.8) × (5)
= 4.0kgms
Final momentum
= (0.8) × (– 5)
= – 4.0kgms
Impulse on ball
= Change in momentum
= 4.0 – (– 4.0)
= 8.0.0kgms

46.The force between the molecules of a liquid in contact with that of a solid is?





A. Adhesive
B. Cohesive
C. Magnetic
D. Repulsive

Correct Answer: Option B
Explanation Cohesion is the inter-molecular attractive force acting between two adjacent portions of a substance, particularly of a solid or liquid. It is this force that holds a piece of matter together



47.A body of mass 100g moving with a velocity if 10ms-1 collides with a wall. If after collision it moves with a velocity of 2.0ms−1 in the opposite direction, calculate the change in momentum.
A. 0.8Ns
B. 1.2Ns
C. 12.0Ns
D. 80.0Ns



Correct Answer: Option A
Explanation Momentum = Mass x Velocity
Change in Momentum = Mass x (change in velocity)
Change in Momentum = Mass x (v - u)
Mass = 100g = 0.1kg
U = 2ms−1
V = 10ms−1
Change in momentum = m (v − u)
= 0.1 (10 − 2)
= 0.1 (8)
= 0.8Ns


48.A 20kg mass is to be pulled up a slope inclined at 30° to the horizontal. If efficiency of the plane is 75%. The force required to pull the load up the plane is J [g=10ms]
A. 87N
B. 73.5N
C. 133.3N
D. 533.2N

Correct Answer: Option C
Explanation V. R =
m = 20kg
V.R =
= 2
Efficiency = 75%
Load = mg
= 20 x 10 = 200N
Efficiency =
75/100 =
M .A =
M. A = 1.5
Since M. A. =
Force =
= 133.3N

49. The tendency of a body to remain at rest when a force is applied to it is called.
A. Impulse
B. Momentum
C. Inertia
D. Friction



Correct Answer: Option C
Explanation Inertia, property of a body by virtue of which it opposes any agency that attempts to put it in motion or, if it is moving, to change the magnitude or direction of its velocity. Inertia is a passive property and does not enable a body to do anything except oppose such active agents as forces and torques. A moving body keeps moving not because of its inertia but only because of the absence of a force to slow it down, change its course, or speed it up.
There are two numerical measures of the inertia of a body: its mass, which governs its resistance to the action of a force, and its moment of inertia about a specified axis, which measures its resistance to the action of a torque about the same axis.


50. An object is placed 20cm from a concave mirror of focal length 10cm. The linear magnification of the image produced is?

A. 0
B.
C. 1
D. 2



Correct Answer: Option C
Explanation = –
= –
= V
V = 20cm.
M =
=
= 1