2011 - WAEC Physics Past Questions and Answers - page 3

21
A metal of mass 200g at a temperature of 100oC is placed in 100g of water at 25oC in a container of negligible heat capacity. If the final steady temperature is 30oC, calculate the specific heat capacity of the metal. [specific heat capacity of the water is 4200 Jkg-1 K-1]
A
150 Jkg-1K-1
B
300 Jkg-1K-1
C
320 Jkg-1K-1
D
1960 Jkg-1K-1
correct option: a
MC$$\theta$$metal = MC$$\theta _{water}$$

0.2 x C x 70 = 0.1 x 4200 x 5

C = 150
22
Ether produces a cooling effect when it is poured on the hand because it has
A
low conductivity
B
high conductivity
C
high latent heat of vaporization
D
low latent heat of vaporization
correct option: c
23
Which of the following statements about the image formed by a plane mirror is not correct?
A
it is laterally inverted
B
it has unit magnifiation
C
it is formed by actual intersection of rays
D
its distance from the mirror is equal to that of the object from the mirror
correct option: c
24
The image formed by a convex mirror is always
A
real, erect and diminished
B
real, inverted and diminished
C
virtual, inverted and diminished
D
virtual, erect and diminshed
correct option: d
25
A ray undergoes a minimum deviation at 40o when it is incident on equilateral triangular glass prism. Calculate the refractive index of the prism
A
1.48
B
1.50
C
1.53
D
1.67
correct option: c
n = $$\frac{\sin \frac{1}{2} (dm + A)}{\sin \frac{1}{2} A}$$

= $$\frac{\sin \frac{1}{2} (40 + 60)}{\sin \frac{1}{2} \times 60}$$

= 1.532
26
Total internal reflection occurs in an optical prism when light rays
A
travel from the prism into an optically denser medium
B
are incident in the prism at an angle greater than the critical angle
C
are incident normally in the prism
D
travel from the prism to the air
correct option: b
27
The speed of light in a certain medium is V while its speed in a vacuum is C. The absolute refractive index of the medium is
A
C + V
B
$$\frac{C}{V}$$
C
$$\frac{V}{C}$$
D
C - V
correct option: b
28
An object is placed 20.0cm in front of a converging lens of focal length 15.0cm. Calculate its image distance
A
1.3cm
B
8.6cm
C
35.0cm
D
60.0cm
correct option: d
$$\frac{1}{v} = \frac{1}{f} - \frac{1}{U}$$

$$\frac{1}{15} - \frac{1}{20} = 60cm$$
29
Presbyopia is a defect of the eye resulting from
A
weak ciliary muscles
B
short eyeball
C
loss of sphericity of the lens
D
long eyeball
correct option: a
$$\frac{f_2}{f_1}$$
1 - $$\frac{f_2}{f_1}$$
$$\frac{f_2}{f_1}$$ - 1
$$\frac{f_1}{f_2}$$