1998 - WAEC Physics Past Questions and Answers - page 3
21
A waterfall is 1.260m high. Calculate the change in temperature of a quantity of water that falls from the top to the bottom of the waterfall. (Neglect heat losses to the surroundings, take g as 10m-2 and specific heat capacity of water as 4200Jkg-1K-1)
A
0.3oC
B
3.0oC
C
33.3oC
D
42.0oC
correct option: b
\(\Delta t = \frac{gh}{c} = \frac{1260 \times 10}{4200}\)
= 3.0o
Users' Answers & Comments= 3.0o
22
A piece of metal is heated until it becomes red-hot, it is then quickly transferred into a beaker containing boiling water. What effect will this have on the boiling water?
A
the boiling water rises slightly
B
the boiling point rises sharply
C
the rate of vaporisation of the boiling water increases
D
the boiling point first rises and then falls
correct option: c
Users' Answers & Comments23
A 90-W immersion heater is used to supply energy for five minutes. The energy supplied is used to completely melt 180g of a solid at is melting point. Neglecting energy losses to the surroundings, calculate the specific latent heat of fusion of the solid
A
0.5Jg-1
B
2.5Jg-1
C
15.0Jg-1
D
450.0Jg-1
correct option: b
Pt = mL
L = \(\frac{pt}{m} = \frac{90 \times 5}{180}\)
= 2.5
Users' Answers & CommentsL = \(\frac{pt}{m} = \frac{90 \times 5}{180}\)
= 2.5
24
If an ebonite rod is rubbed with fur
A
both the ebonite rod and the fur will be negatively charged
B
the ebonite rod will be positively charged while the fur will have no charge
C
there will be electron transfer only if the ebonite rod is earthed
D
the ebonite rod will be negatively charged while the fur will be positively charged
correct option: d
Users' Answers & Comments25
An eclipse of the sun by the moon occurs when the sun, the moon and the earth are in a straight line and the
A
earth casts a shadow on the moon
B
moon casts a shadow on the sun
C
moon is between the sun and the earth
D
earth is between the sun and the moon
correct option: c
Users' Answers & Comments26
The phenomenon which occurs when light changes direction as it passes from one medium to another is called
A
reflection
B
polarisation
C
interference
D
diffraction
correct option: e
Users' Answers & Comments27
What is the image distance of an object placed at a distance of 2f from a converging lens of focal length f?
A
f/4
B
f/2
C
f
D
2f
correct option: d
Users' Answers & Comments28
The images formed by diverging lenses are always
A
diminished, virtual and inverted
B
diminished, virtual and errect
C
diminished inverted and real
D
magnidied, virtual and errect
correct option: b
Users' Answers & Comments29
A converging lens of focal length 5cm is used as a magnifying glass by a man whose nearpoint is 35cm. Calculate the magnification given by the lens
A
8
B
7
C
6
D
5
correct option: c
\(\frac{1}{f} = \frac{1}{u} + \frac{1}{v}\)
= \(\frac{1}{5} - \frac{1}{35} = \frac{30}{175}\)
U = \(\frac{175}{30}\) = 5.8m
\(\frac{v}{u} = \frac{35}{5.8}\)
= 6
Users' Answers & Comments= \(\frac{1}{5} - \frac{1}{35} = \frac{30}{175}\)
U = \(\frac{175}{30}\) = 5.8m
\(\frac{v}{u} = \frac{35}{5.8}\)
= 6
30
An astronomical telescope having an objective of focal length 100cm and an eyepiece of focal length 10cm is used in normal adjustment, calculate the separation of the lenses
A
0.10m
B
0.90cm
C
1.10m
D
1.80m
correct option: c
Users' Answers & Comments