2019 - JAMB Physics Past Questions & Answers - page 8

71

In the molecular explanation, heat is transferred by the

A

free electrons

B

free atoms

C

free molecules

D

free solids

CORRECT OPTION: a

Conduction is as a result of free electrons
Convection as a result of  the movement of the fluid involved
Radiation as a result of electromagnetic waves.

72

Which of these is observed when air is pumped out of a discharge tube without lowering its pressure

A

the conductivity of the air increases

B

the conductivity of the air decreases

C

conduction does not occur

D

spark are produced

CORRECT OPTION: c
73

Which of the following characteristics of a wave is used in the measurement of the depth of the Sea?

A

diffraction

B

interference

C

refraction

D

reflection

CORRECT OPTION: d

Sea depth can be measured using the echo reflected in sound waves.

74

If the attraction of the sun is suddenly ceased, the earth would continue to move in a straight line making a tangent with the original orbit. This statement is derived from Neutron's

A

First law of motion

B

Second law of motion

C

Third law of motion

D

Law of universal gravitation

CORRECT OPTION: a

Newton's First law of motion states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force

75

Heat may be transferred by conduction, convention and radiation. By which of these methods does heat travel through vacuum?

A

Conduction only

B

Convection only

C

Radiation only

D

All these methods

CORRECT OPTION: c
76

The part of the human eye that does similar work as the diaphragm of a camera lens is the

A

Ciliary muscles

B

Pupil

C

Iris

D

Retina

CORRECT OPTION: c
77

Workdone on an object to bring it to a certain point in space is called

A

Gravitational potential energy

B

Potential energy

C

Kinetic energy

D

Mechanical energy

CORRECT OPTION: a

Gravitational energy is the potential energy a physical object with mass has in relation to another massive object due to gravity. It is potential energy associated with the gravitational field. Gravitational energy is dependent on the masses of two bodies, their distance apart and the gravitational constant. Wikipedia

78

A copper rod, 5m long when heated through 20c, expands by 1mm. If a second copper rod, 2.5m long is heated through 5c, by how much will it expand?

A

4mm

B

A. 2mm

C

B. 0.25mm

D

0.12mm

CORRECT OPTION: b

l\(_1\) = 5m, ΔT = 10c, l\(_2\) - l\(_1\) = 1mm
l\(_1\)  = 2.5m, ΔT = 5c, l\(_2\) - l\(_1\) = ?

α = l\(_2\) - l\(_1\)
l\(_1\)ΔT

 

1
5(10)
= l\(_2\) - l\(_1\)
2.5(5)

 

l\(_2\) - l\(_2\) = 2.5(5)
5(10)
= 1
4
= 0.25mm
79

A safety precaution designed to prolong the life of a lead acid accumulator is

A

By topping up the cells with concentrated acid

B

The use of naked flame when charging the battery

C

Keeping the specific gravity of the electrolyte within specified range

D

By connecting wires to the terminals directly when testing the level of charging

CORRECT OPTION: c
80

The mass of water vapour in a given volume of air is 0.05g at 20°C, while the mass of water vapour required to saturate it at the same temperature is 0.15g. Calculate the relative humidity of the air.

A

3.33%

B

5.55%

C

33.33%

D

55.55%

CORRECT OPTION: c
RH = mass of water vapour in volume of air
mass of water vapour for saturation

 

RH = m
M
= 0.05
0.15
× 100 = 5
0.15
= 500
15
= 33.33%

RH = 33.33%

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