Physics JAMB Practice CBT Questions & Answers 2021 Set 3

1. Which is the incorrect formula for a body accelerating uniformly?

A. a = v² − u22

B. v² = u² + 2as
C. s = ut + 12at²
D. v² − u²= 2as

Correct Answer: Option A

Explanation

Look through the equations of motion

2.Which of the following is not an electromagnetic radiation?

A. x - ray
B. Radio waves
C. sunlight
D. sound waves

Correct Answer: Option D

Explanation

Electromagnetic waves do not require any material medium, but sound waves is a mechanical wave that require a material medium

3. Calculate the electric field intensity between two plates of potential difference 6.5V when separated by a distance of 35cm.

A. 18.57NC−1

B. 53.06N C−1
C. 2.28NC−1
D. 0.80NC−1

Correct Answer: Option A

Explanation

Electric Field Intensity (E) = vd

= potential differencedistance

= 6.5v35cm

= 6.535×10−2

= 18.57NC−1

4. Why do soldiers march disorderly while crossing a bridge?

A. To prevent resonance on the bridge
B. To set the bridge into resonance
C. To make the b ridge collapse
D. To spread their weight evenly on the bridge

Correct Answer: Option A

Explanation

Soldiers march disorderly while crossing a bridge to prevent resonance because when soldiers march in orderly manner across a bridge, they generate a rhythmic oscillation of wave on the bridge and at a certain point, would start oscillation to the same rhym as that of the marching steps. This oscillation would reach a maximum peak when the bridge can no longer sustain its own strength and hence collapses. So for this reasons, soldier are ordered to march disorderly while crossing a bridge

5. Calculate the upthrust on an object of volume 50cm3 which is immersed in liquid of density 103kgm-3 [g = 10ms-2]

A. 0.8N
B. 2.5N
C. 0.5N
D. 1.0N

Correct Answer: Option C

Explanation

Upthrust = change in weight

density = massvolume

Mass of liquid displaced = Density of Liquid × Volume;

= 103×50×10−6m3

= 0.05kg

(Note that the volume of 50cm3 was converted to m3 by multiplying by 106) i.e 50cm3=50×10−6m3

Since mass displaced = 0.05kg

Upthrust = mg = 0.05 × 10

= 0.5N

6.Under what conditions are cathode rays produced in a discharge tube?

A. High pressure and low voltage
B. High pressure and high voltage
C. Low pressure and low voltage
D. Low pressure and high volatge

Correct Answer: Option D

Explanation

Cathode rays are produced in a discharge tube under Low pressure and high voltage

7.Under which of the following conditions is workdone

A. A man supports a heavy food above his head with his hands
B. A boy climbs onto a table
C. A man pushes unto a table
D. A woman holds a pot of water

Correct Answer: Option B

Explanation

For work to be done, distance must be involved because

workdone = force × distance

8.Calculate the specific latent heat of vaporization of steam of 1.13 x 106J of heat energy is required to convert 15kg of steam to water.

A. 7.53 x 105 Jkg−1

B. 7.53 x 10-2Jkg−1
C. 7.53×104Jkg−1
D. 7.53 x 10-3Jkg−1

Correct Answer: Option C

Explanation

Quantity of heat = mass(m) × specific latent heat (L)

Q = mL

L = Qm

= 1.13×10615

= 7.53×104Jkg−1

9.A cell of internal resistance 2 π supplies current to a 6 π resistor. The efficiency of the cell is

A. 12.0%
B. 25.0%
C. 33.3%
D. 75.0%

Correct Answer: Option C

Explanation

Internal resistance determine the maximum current that can be supplied

Efficiency = rR

× 100

= 26 × 100

= 33.3%

10.Which of the following statements is NOT correct?

A. Molecules of a liquid are stationary
B. Brownian motion is an evidence of particle nature of matter
C. Matter is made up of molecules
D. The molecules of matter are in constant motion

Correct Answer: Option A

Explanation

Molecules of liquid are not stationary

Brownian motion is an evidence of particle nature of matter

matter is made up of molecules

The molecules of matter are in constant motion

11.A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine

A. 80.0%
B. 76.6%
C. 66.7%
D. 60.7%

Correct Answer: Option C

Explanation

Efficiency = maV.R x 1001

V.R = number of pulleys = 6

ma = LoadEffort = 20050 = 4

Effiecieny = 46 × 100 = 66.67%

12. Three 3ω resistance are connected in parallel what is the equivalent resistance?

A. 1ω
B. 9ω
C. 3ω
D. 0.33ω

Correct Answer: Option A

Explanation

Resistor connected in a parallel have an equivalence given by

1Reff = 13 + 13 + 13

= 1+1+13 = 33 = 1

Reff = 1ω

13.Which of the following instruments helps to maintain the correct humidity and temperature of a building?

A. A compressor
B. A refrigerator
C. Air blower
D. Air conditioner

Correct Answer: Option D

Explanation

Compressor is an instrument to supply air or other gas at increased pressure

Refrigerator is an appliance to keep things cold

Air blower is used to release air

Air conditioner is used to remove heat and maintain a stable temperature in an occupied space

14. An element and its isotope only differ in the number of

A. protons
B. electrons
C. ions
D. neutrons

Correct Answer: Option D

Explanation

Isotopy is due to difference in mass number, what causes the difference is the difference in the number of neutrons present

15.The thermal expansion of a solid is an advantage in

A. Balance wheel of a watch
B. Construction of steel rail lines
C. Construction of large steel bridges
D. Fitting of tyres on wheels

Correct Answer: Option A

Explanation

Thermal expansion of a solid is majorly advantageous in the use of bimetallic strip in the balance of a watch so as not to lose time

16. The S.I unit of moment of a force is

A. kgm
B. µm
C. Jm
D. µm−1

Correct Answer: Option B

Explanation

Moment of a force is the product of a force and the perpendicular distance from the line of action of the force

Moment = force × distance

= N × m

= Nm

17.A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine

A. 80.0%
B. 76.6%
C. 66.7%
D. 60.7%

Correct Answer: Option C

18.Calculate the light of the image formed by a pinhole camera of length 12cm used to photograph an object 60cm away from the hole and 70cm high

A. 10 cm
B. 16 cm
C. 5 cm
D. 14 cm

Correct Answer: Option D

Explanation

Magnification = Length of cameradistance of object from pin hole

m = 1260

= 0.2

Also magnification m = Height of imageHeight of object

∴ Height of image = m × height of object

= 0.2 × 70

= 14cm

19. When two objects P and Q are supplied with the same quantity of heat, the temperature change in P is observed to be twice that of Q. The mass of P is half that of Q. The ratio of the specific heat capacity pf P to Q is

A. 1:4
B. 4:1
C. 1:1
D. 2:1

Correct Answer: Option C

Explanation

H = mcθ

H_P = H_Q, θ_P = 2θ,

m_P = 12m_Q

∴ H_P = m_QC_Pθ_P, also HQ = m_QC_Qθ_Q

Since H_P = H_Q

∴ m_Pc_Pθ_P = m_Qc_Pθ_q

Putting in the conditions

12m_Q × c_P × 2θ_Q = m_Q × θ_Q × c_Q

∴ c_P = c_Q

CpCQ= 11

= 1:1

20. When the r.m.s value of a source of electricity supply is given as 240v, it means that the peak value of the supply is

A. 240v
B. 340v
C. 480v
D. 57600v

Correct Answer: Option B

Explanation

The relationship between the peak value and r.m.s value of electricity supply is given as

Vr.m.s = Vo2√

where V_o = peak voltage

∴ V_o = Vr.m.s × √2

= 240 × √2

= 339.5v

= 340v

21 Which of the following operations can be used to convert an alternative current dynamo into a direct current dynamo

- A. number of turns in the coil is increased
- B. strength of the field magnet is increased
- C. slip rings are replaced with split ring cummutator
- D. coil is wound on a soft iron armature
Correct Answer: Option C
Explanation
A d.c generator is one in which its current is allowed to flow in one direction even through it may vary in value an a.c generator can only be made to produce a d.c by replacing the two slip rings with a single split ring or commutator.
22
The net capacitance in the circuit above is
- A. 80µF
- B. 6.0µF
- C. 4.0µF
- D. 2.0µF
Correct Answer: Option D
Explanation
For capacitance i n parallel, 2µF and 2µF are in parallel,
their equivalence is 2µF and 2µF = 4µF
The 4µF generated is now in series with the remaining 4µF.
The net capacitance for series connection is
1C = 14 + 14 = 1 + 14 = 24
C = 42
= 2µF
23. The instrument used to measure the pressure of a gas is
- A. barometer
- B. thermometer
- C. hygrometer
- D. manometer
Correct Answer: Option D
Explanation
Barometer is used to measure atmosphere pressure
Thermometer is used to measure temperature
Hygrometer is used to measure relative density of a liquid
Manometer is used to measure the pressure of a gas
24.A man of mass 50kg ascends a flight of stains 5m high in 5 seconds. If acceleration due to gravity is 10ms−2
the power expended is
- A. 100w
- B. 200w
- C. 400w
- D. 500w
Correct Answer: Option D
Explanation
Power is the time rate of doing work
i.e power = energytime
Since energy = mgH
∴ power = mgHt
= 50×10×5t
= 500W
25. .A radio station broadcast at a frequency of 600KHZ. If the speed of light in air is 3 × 108ms−1. Calculate the wavelength of the radio wave
A. 2.20 × 103m
B. 5.0 × 102m
C. 5.0 × 105m
D. 11.8 × 1011m
Correct Answer: Option B
Explanation
V = fλ
λ = vf
= 3×108600×103 = 500m
= 5 × 10²m
N.B 600KHz Frequency = 600 × 10³Hz
26 Which of the following is a scalar quantity?
- - A. Tension
  - B. Weight
  - C. Impulse
  - D. Mass
  Correct Answer: Option D
  Explanation
  Scalar quantity is a quantity with only magnitude, it has no direction
  Tension, weight, impulse are vector quantities because they have direction. Mass is the only scalar quantity there
  27.Determine the focal length of a thin converging lens if the power is 5.0 dioptres
  - A. 0.1 m
  - B. 0.2 m
  - C. 2.0 m
  - D. 2.5 m
  Correct Answer: Option B
  Explanation
  Power of a lens = 1f
  f = focal length
  f = 1p
  = 15
  = 0.2m
  28.A string of length 5cm is extended by 0.04m when a load of 0.8kg is suspended at the end. How far will it extend if a force of 16N is applied? [g = 10ms−2]
  - A. 0.04m
  - B. 0.12m
  - C. 0.01m
  - D. 0.08m
  Correct Answer: Option D
  Explanation
  From Hoke's Law, F = ke, K = Constant of Force
  For he first case, Force = mg,
  = 0.8 × 10 = 8N
  ∴ 8 = k × 0.04
  k = 80.04
  = 200Nm
  Since K is constant
  For the second case, F = ke
  F = 200 × e
  ∴ e = F200
  = 16200
  = 0.08m
  29. How can energy loss be minimized through Eddy-current?
  - A. By using high resistance wire
  - B. By using insulated soft iron wires
  - C. By using low resistance wires
  - D. Bu using turns of wires
  Correct Answer: Option A
  Explanation
  Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core
  Usage of insulated soft iron wire is to reduce hysteresis loss
  Usage of low resistance wire (thick wire) is to reduce I2R loss
  Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux
  Thus the correct answer is to use high resistance wire or thin wire
  30
  From the diagram above, calculate the energy stored in the capacitor
  A. 4.0 x 10−2
- B. 4.0 x 10−4J
- C. 8.0 x 10−4J
- D. 8.0 x 10−2
Correct Answer: Option B
Explanation
c = 8µF, v = 10v
Energy stored = 12
cv²
= 12 × (8 × 10− 6) × 10²
= 4 × 10−4
31. A constant force of 5N acts for a 5 seconds on a mass of 5kg initially at rest. Calculate the final momentum
A. 125kgms−1
B. 25kgms−1
C. 15kgms−1
D. 0kgms−1
Correct Answer: Option B
Explanation
Impulse = momentum
Impulse = Force (f) × time (t)
Momentum = mass (m) × velocity (v)
∴ Ft = Final momentum - initial momentum
FT = mv - mu
Since it is initially at rest u = 0
∴ 5 × 5 = mv − m(0)
25 = mv
∴ Final momentum = 25kgms−1
32. I. Refraction II. Interference III. Diffraction Which of the above properties are common to all waves?
- A. II and III only
- B. I, II and III
- C. I and II only
- D. I and III only
Correct Answer: Option B
Explanation
Refraction, Interference and diffraction are all properties of waves
33. I. Refraction II. Interference III. Diffraction Which of the above properties are common to all waves?
- A. II and III only
- B. I, II and III
- C. I and II only
- D. I and III only
Correct Answer: Option B
Explanation
Refraction, Interference and diffraction are all properties of waves
34. Which of the following is correct about an electric cell?
- A. Primary cell produces a large current for a long time
- B. Secondary cell has a very high internal resistance
- C. Primary cell has a very low internal resistance
- D. Secondary cell has a very low internal resistance
Correct Answer: Option D
Explanation
About electric cell
Primary cells are used up gradually often the cells are use and it can't be recharged
Secondary cells or accumulated can be recharged and used for a long period of time and their main advantage is that they have low internal resistance
35.Which of the following is a semiconductor
- A. copper
- B. silicon
- C. plastic
- D. Iron
Correct Answer: Option B
Explanation
Semi-conductor have an elecctric conductivity intermediate in value between that of a pure metal and a good insulator. Silicon is an example
36. Which of the following surfaces will absorbs radiant heat energy heat?
- A. white
- B. red
- C. black
- D. blue
Correct Answer: Option C
Explanation
A black solution is a better radiator of heat and allow a better absorber of heat.
37. It is known that a neutron exists in a light atomic nucleus
Which of the following also exists in the nucleus?
- A. An electron
- B. A β - particle
- C. β - particle
- D. proton
Correct Answer: Option D
Explanation
Nucleus of atom is made up of neutron and proton
38.The instrument to measure the relative density of liquid is
A. thermometer
B. hydrometer
C. spring balance
D. beaker
Correct Answer: Option B
Explanation
Thermometer is used to measure temperature
Hydrometer is used to measure relative density of liquid.
Spring balance is used to measure the weight of an object
Beaker is used to measure or take volume of a liquid
39.What is the speed of a body vibrating at 50 cyclic per second
- A. 100 πrads−1

B. 200 πrads−1
C. 50 πrads−1
D. 400 πrads−1

Correct Answer: Option A

Explanation

1 cycle = 3600 = 2π rad

∴ 50 cycle = 2 π rad × 50 = 100 πrad

∴ = angular speed = 50 cycles per seconds = 100 π rads−1

40. The action of blotting paper on ink is due to

A. diffusion
B. osmosis
C. capillarity
D. surface tension

Correct Answer: Option C

Explanation

Capillarity is the tendency of a liquid to rise or fall in a narrow tube and it explains why a blotting paper absorbs ink

41. When two mirrors are placed at an angle of 900 to each other, how many images will be formed when an object is placed in front of the mirrors

A. 5
B. 4
C. 3
D. 2

Correct Answer: Option C

Explanation

When two mirror are inclined at an angle θ, the number of images formed, n = 360θ − 1

∴ since θ = 90^o

∴ 360θ − 1

= 4 − 1

= 3

42. If silicon is doped with phosphorus, what type of semiconductor material will be formed?

A. Zener material
B. P-n junction
C. n-type
D. p-type

Correct Answer: Option C

Explanation

When silicon is doped with a trivalent atom. A p-type semi-conductor will be formed when silicon is doped with a pentavalent atom such as arsenic, a n-type semi-conductor will be formed

Phosphorous is a pentavalent element, so it will produce a o -type semi-conductor

43..Calculate the angle of minimum deviation of a 60^o prism of a refractive index [sin^-10.75 = 49^o]

A. 38.00^o
B. 19.47^o
C. 16.25^o
D. 49^o

Correct Answer: Option A

Explanation

For a refractive index () = sin12(A+D)sin12A

D = angle of minimum deviation

A = refractive angle of the prism

1.5 = sin12(60+D)sin12×60

1.5 = sin12(60+D)sin30

Sin 12 (60 + D) = 1.5 * Sin 30

Sin 12 (60 + D) = 0.75

12 (60 + D) = Sin^-1 (0.75)

but Sin^-1 (0.75) = 49^o

(60 + D) = 49

60 + D = 2 * 49 = 98^o

D = 98^o - 60^o

D = 38^o

44.What is the cost of running seven 40 W lamps and five 80 W la mps for 12 hours of the electrical energy cost N7.00kWk?

A. N80.00
B. N45.36
C. N65.00
D. N57.12

Correct Answer: Option D

Explanation

Seven 40W lamps = 7 × 40 = 280W

Five 80W lamps = 5 × 80 = 400W

Total power = 280W + 400W

= 680W

= 680KW1000 = 0.68KW

The kilowatt hour = 0.68 KW × 12 hrs

= 8.16 KWh

Cost is N 7 per KWh

So the cost of running them = 8.16KWh × N 7/KWh

= 57.12

From the diagram above, calculate the total current in the circuit

A. 5.0A
B. 3.7A
C. 4.5A
D. 4.0A

From the diagram above, calculate the total current in the circuit

A. 5.0A
B. 3.7A
C. 4.5A
D. 4.0A

Correct Answer: Option B

Explanation

V = IR from ohms law

I = VR

Since the resistance are in parallel

1Reff = 18 + 112 + 16

= 2+3+636 = 1136

Reff = 3611 = 3.27

I = I₁ + I₂ + I₃

= VReff= 123.27

= 3.669A

I = 3.7A

46.Calculate the time taken for a mango fruit that fall from the tree 20 m to the ground [g = 10 ms^-2]

A. 10s
B. 5s
C. 4s
D. 2s

Correct Answer: Option D

Explanation

u = , H = 20, g = 10

From equation of motion under gravity

H = ut ± 12gt², It is falling so g is +ve

H = 0 + 12gt²

H = 12gt²

2H = gt²

2Hg = t²

t = 2H√g

= 2×20√10

= √4

= 2s

47.Which of the following is not a mechanical wave?

A. wave in closed pipe
B. radio waves
C. water waves
D. sound waves

Correct Answer: Option B

Explanation

Mechanical waves require material medium for their propagation only radio waves among the options docs require a material medium

48. The velocity ratio of an inclined plane where angle of inclination in θ is

A. Sinθ
B. Cosθ
C. Tanθ
D. 1sinθ

The velocity ratio of an inclined plane where angle of inclination in θ is

A. Sinθ
B. Cosθ
C. Tanθ
D. 1sinθ

Correct Answer: Option D

Explanation

Consider an inclined plane shown below, as the effort moves along OB, the load moves is lifted up through a vertical height AB

V.R = distance moved by effortdistance moved by load

= OBAB

But Sinθ = opphyp = ABOB

therefore; = OBAB = 1sinθ

49.The volume of a fixed mass of gas is 10cm³ when its pressure is 400cmHg. Determine the volume of the gas when its pressure is 200cmHg.

A. 30cm³
B. 40cm³
C. 50cm³
D. 20cm³

Correct Answer: Option D

Explanation

Using boyle's law

P₁V₁ = P₂V₂

V₂ = P1V1200 = 400×10200

= 20cm³

50.Which of the following representations is correct for an atom X with 28 electrons and 30 neutrons?

A. 5828X

B. 3028X
C. 2830X
D. 5830X

Correct Answer: Option A

Explanation

An atom can be represented thus,

ZAX where Z = mass number

A = atomic number

A = number of proton = number of electrons in a free state = 28

Z = number of protons + number of neutrons = 28 + 30 = 58

5828Xis the representation

51. 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

52.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

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Physics JAMB Practice CBT Questions & Answers 2021 Set 3