2003 - JAMB Physics Past Questions and Answers - page 2
11
ToC051015204060S.V.P(mmHg)4.586.518.9412.6717.5055.10149.00
The table above shows the saturation vapour pressure against temperature in a certain town. If the vapour pressure in this town at 20oC is 10mmHg, what is the relative humidity?
The table above shows the saturation vapour pressure against temperature in a certain town. If the vapour pressure in this town at 20oC is 10mmHg, what is the relative humidity?
A
170.0%
B
57.0%
C
17.5%
D
10.0%
correct option: b
R.H = Partial Pressure of Water Vapour Presentx100_1S.V.P at temperature of atmosphere
= _10x100_117.50
= 57.14%
Users' Answers & Comments= _10x100_117.50
= 57.14%
12
A turning fork of frequency 340Hz is vibrated just above a cylindrical tube of height 1.2m. If water is slowly poured into the tube, at what maximum height will resonance occur.
[speed of sound in air = 340ms-1]
[speed of sound in air = 340ms-1]
A
0.95m
B
0.60m
C
0.50m
D
0.45m
correct option: d
In vibration in a closed pipe/tube, the first resonance occurs at a position L = V/4f,
when reading from the top of the tube,
= 0.25m
L2 = 3V/4f
= 0.75m
L3 = 5V/4f
= 1.25m
However, the effective length of the tube is 1.2m. Thus reading from below, the first position of resonance will be 1.20 - 0.75m = 0.45m
Users' Answers & Commentswhen reading from the top of the tube,
| L1 = | _340 |
| 4 x 340 |
= 0.25m
L2 = 3V/4f
| L2 = | 3 x 340 |
| 4 x 340 |
= 0.75m
L3 = 5V/4f
| L3 = | 5 x 340 |
| 4 x 340 |
= 1.25m
However, the effective length of the tube is 1.2m. Thus reading from below, the first position of resonance will be 1.20 - 0.75m = 0.45m
13
By what factor will the size of an object placed 10cm from a convex lens be increased if the image is seen on a screen placed 25cm from the lens?
A
15.0
B
2.5
C
1.5
D
0.4
correct option: b
Form the lens formula = 1/U + 1/V = 1/f
=> 1/10 + 1/25 = 1/f;
∴ (5 + 2) / 50 = 1/f
∴ f = 50/7cm
since the image is observed on a screen, it is a real image. Thus magnification
M = f/U-f
= 50/7 x 7/20 = 2.5
Users' Answers & Comments=> 1/10 + 1/25 = 1/f;
∴ (5 + 2) / 50 = 1/f
∴ f = 50/7cm
since the image is observed on a screen, it is a real image. Thus magnification
M = f/U-f
| = | __50/7 |
| 10 - 50/7 |
| ∴ M = | 50/7 |
| 20/7 |
= 50/7 x 7/20 = 2.5
14
Thermal equilibrium between two object exist when
A
the temperature of both objects are equal
B
the quantity of heat of both objects is the same
C
the heat capacities of both objects are the same
D
one object losses heat continuously to the other
correct option: a
Two thermal objects are said to be in a thermal equilibrium when the temperature of both objects are equal. Generally, heat flows from an object at a higher temperature to the one at a lower temperature until both temperature are the same, during which the two bodies are said to be in thermal equilibrium
Users' Answers & Comments15
An open pipe closed at one end produces its first fundamental note. If the velocity of sound in air is P and t the length of the pipe, the frequency of the note is
A
2v/t
B
v/5t
C
v/4t
D
v/2t
correct option: c
In vibration in a closed pipe/tube as shown in the figure, fundamental note is produced at the first position of resonance. When the length of the air column L = λ/4; => λ = 4L. Since the open end of the tube is taken as an antinode; and closed end as the node.
Thus the associated frequency is given by
f = V/λ = V/4L
∴ f = V/4L
Users' Answers & CommentsThus the associated frequency is given by
f = V/λ = V/4L
∴ f = V/4L
16
On a fairly cool rainy day when the temperature is 20oC, the length of a steel railroad track is 20m. What will be its length on a hot a dry day when the temperature is 40oC?
[coefficient of linear expansion of steel = 11 x 10-6K-1]
[coefficient of linear expansion of steel = 11 x 10-6K-1]
A
20.013m
B
20.009m
C
20.004m
D
20.002m
correct option: c
The increase in length of the steel rail is given by
= α 10
= 11 x 10-6 x 20 x (40 -20)
= 11 x 10-6 x 20 x 20
= 4.4 x 10-3
∴ Final length will be original length plus increase in length
= 20 + 4.4 x 10-3
= 20 + 0.0044
= 20.0044m
Users' Answers & Comments= α 10
= 11 x 10-6 x 20 x (40 -20)
= 11 x 10-6 x 20 x 20
= 4.4 x 10-3
∴ Final length will be original length plus increase in length
= 20 + 4.4 x 10-3
= 20 + 0.0044
= 20.0044m
17
If an object is placed between two parallel plane mirrors with their reflecting surfaces facing each other, how many images of the object will be formed?
A
Infinite
B
Eight
C
Four
D
Two
18
The phenomenon where by the water droplets in the atmosphere combines with dust particles in the air to reduce visibility is
A
cloud
B
mist
C
hail
D
fog
correct option: d
Users' Answers & Comments19
At what position will an object be placed in front of a concave mirror in order to obtain an image at infinity?
A
At the pole of the mirror
B
At the principal focus
C
at the center of the curvature
D
Between the principal focus and the center of curvature
correct option: b
For a concave mirror to produce an image at infinity, the image has to be place at the principal focus of the mirror
Users' Answers & Comments20
If the distance from a point source of sound is doubled, by what factor does the intensity decrease?
A
4.00
B
2.00
C
0.50
D
0.25
correct option: a
In general intensity of a wave is the rate of flow of energy across unit area normal to the direction of propagation of the wave intensity α1/r2 where r is the distance away from the point source. Thus if the distance from the point source of the sound wave is doubled, then the intensity will be decreased by a factor of 4
Users' Answers & Comments