1990 - JAMB Physics Past Questions and Answers - page 2
11
The resistances of platinum wire at the ice and steam points are 0.75 ohm and 1.05 ohm respectively. Determine the temperature at which the resistance of the wire is 0.90 ohm
A
43.0oC
B
50.0oC
C
69.9oC
D
87.0oC
correct option: b
100oC .... 1.05\(\theta\)
\(\theta\)oC .... 0.9\(\theta\)
0oC .... 0.75\(\theta\)
\(\frac{\theta - 0}{100 - 0}\) = \(\frac{0.9 - 0.75}{1.05 - 0.75}\)
\(\theta\) = 50oC
Users' Answers & Comments\(\theta\)oC .... 0.9\(\theta\)
0oC .... 0.75\(\theta\)
\(\frac{\theta - 0}{100 - 0}\) = \(\frac{0.9 - 0.75}{1.05 - 0.75}\)
\(\theta\) = 50oC
12
A bar of initial length /0 is heated through a temperature change \(\Delta\)t to a new length I. The linear expansivity, a, of the bar is
A
\(\frac{/ - /_o}{/ \Delta t}\)
B
\(\frac{/ - /_o}{/_o \Delta t}\)
C
/o(1 + \(\Delta\) t)
D
\(\frac{/ - /_o}{/(1 + \Delta t)}\)
13
The pressure of a gas when cooled at constant volume will decrease because the molecules
A
collide less frequently with the walls of the container
B
have the same average kinetic energy
C
break up into smaller molecules
D
decrease in number
correct option: a
Users' Answers & Comments14
1kg of copper is transferred quickly from boiling water to a block of ice. Calculate the mass of ice melted, neglecting heat loss. [specific heat capacity of copper 400Jkg-1K-1 and latent heat of fusion of ice 333 x 103Jkg-1]
A
60g
B
67g
C
120g
D
133g
correct option: c
Heat lost = heat gained
1 x 400 x (100 - 0) = m x 333000
m = 0.12kg
converting to grams; 0.12 x 1000
= 120g
Users' Answers & Comments1 x 400 x (100 - 0) = m x 333000
m = 0.12kg
converting to grams; 0.12 x 1000
= 120g
15
Which of the following conditions will make water boil at a temperature of 100oC when the atmospheric pressure is 750mmHg?
A
increase the external pressure
B
reduce the external pressure
C
heat more rapidly at the same pressure
D
reduce the external pressure by a quarter
correct option: a
Users' Answers & Comments16
Which of the following statements? i. land and sea breezes are natural convection currents. ii. convection may occur in liquids or gasses but not in solids. iii. the vacuum in a thermos flask prevents heat loss due to convection only.
A
i and ii only
B
i and iii only
C
i and iii only
D
i, ii, and iii
correct option: a
Users' Answers & Comments17
A light wave of frequency 5 x 1014Hz moves through water which has a refractive index of \(\frac{4}{3}\). Calculate the wavelength in water if the velocity of light in air is 3 x 108ms-1
A
4.5 x 10-7m
B
6.0 x 10-7m
C
1.7 x 106m
D
2.2 x 106m
correct option: a
\(\frac{1}{4}\) = \(\frac{3 \times 10}{v}\)
v = 2.25 x 108ms-1
\(\lambda\) = \(\frac{V}{F}\)
= \(\frac{2.25 \times 10^8}{5 \times 10^14}\)
\(\lambda\) = 0.45 x 10-6m
Users' Answers & Commentsv = 2.25 x 108ms-1
\(\lambda\) = \(\frac{V}{F}\)
= \(\frac{2.25 \times 10^8}{5 \times 10^14}\)
\(\lambda\) = 0.45 x 10-6m
18
A wave disturbance travelling in air enters a medium in which its velocity is less than that in air. Which of the following statements is true about the wave medium?
A
both the frequency of the wave and the wavelength are decreased
B
the frequency of the wave is decreased while the wavelength is increased
C
the frequency of the wave is unaltered while the wavelength is decreased
D
the frequency of the wave is decreased while the wavelength is unaltered
correct option: c
Users' Answers & Comments19
Shadows and eclipses result from the
A
refraction of light
B
rectilinear propagation of light
C
defraction of light
D
reflection of light
correct option: b
Users' Answers & Comments20
An object which is 3cm high is placed vertically 10cm in front of a concave mirror. If this object produces an image 40cm from the mirror, the height of the image is
A
0.75cm
B
4.00cm
C
8.00cm
D
12.00cm
correct option: d
\(\frac{\text {object height}}{\text{image height}}\) = \(\frac{\text {object distance}}{\text{image distance}}\)
\(\frac{3}{\text{image height}}\) = \(\frac{10}{40}\)
Image height = 12cm
Users' Answers & Comments\(\frac{3}{\text{image height}}\) = \(\frac{10}{40}\)
Image height = 12cm