# 2011 - WAEC Physics Past Questions and Answers - page 3

21

A metal of mass 200g at a temperature of 100

^{o}C is placed in 100g of water at 25^{o}C in a container of negligible heat capacity. If the final steady temperature is 30^{o}C, calculate the specific heat capacity of the metal. [specific heat capacity of the water is 4200 Jkg^{-1}K^{-1}]A

150 Jkg

^{-1}K^{-1}B

300 Jkg

^{-1}K^{-1}C

320 Jkg

^{-1}K^{-1}D

1960 Jkg

^{-1}K^{-1}**Answer & Comments**

**correct option:**a

MC\(\theta\)

0.2 x C x 70 = 0.1 x 4200 x 5

C = 150

Users' Answers & Comments_{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

**Answer & Comments**

**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

**Answer & Comments**

**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

**Answer & Comments**

**correct option:**d

25

A ray undergoes a minimum deviation at 40

^{o}when it is incident on equilateral triangular glass prism. Calculate the refractive index of the prismA

1.48

B

1.50

C

1.53

D

1.67

**Answer & Comments**

**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

Users' Answers & Comments= \(\frac{\sin \frac{1}{2} (40 + 60)}{\sin \frac{1}{2} \times 60}\)

= 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

**Answer & Comments**

**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

**Answer & Comments**

**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

**Answer & Comments**

**correct option:**d

\(\frac{1}{v} = \frac{1}{f} - \frac{1}{U}\)

\(\frac{1}{15} - \frac{1}{20} = 60cm\)

Users' Answers & Comments\(\frac{1}{15} - \frac{1}{20} = 60cm\)

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

**Answer & Comments**

**correct option:**a

30

The focal length of the eye-piece of an astronomical telescope is f

_{1}, while the focal length of the object is f_{2}. Fro normal adjustment, the angular magnification is given byA

\(\frac{f_2}{f_1}\)

B

1 - \(\frac{f_2}{f_1}\)

C

\(\frac{f_2}{f_1}\) - 1

D

\(\frac{f_1}{f_2}\)

**Answer & Comments**

**correct option:**a