TEST ON CONCAVE AND CONVEX MIRRORS: ANSWERS

 

1.      Define (a) a real image (b) a virtual image (c) magnification.
ANSWER
(a)  A real image is formed by the actual intersection of light rays.
      It can be projected onto a screen.
(b)  A virtual image is formed by the apparent intersection of light rays.
      It cannot be project onto a screen.
(c)  Magnification is the ratio of the height of the image to the height of the object.
                             

2.      Draw a diagram showing how the image is formed in a concave mirror if the object is
(a)  between the centre of curvature and the focus
(b)  between the focus and the pole.
ANSWER
(a)
     
(b)
     

3.      Give two uses each for (a) a concave (b) a convex mirror.
ANSWER
(a)  A concave mirror can be used as a shaving mirror.
      It is also used by dentists to obtain a magnified image of a tooth.
(b)  A convex mirror is used as a security mirror in shops.
      It is also used as a rear view mirror in cars.

4.      Say how you would find the approximate focal length of a concave mirror using only a concave mirror, a metre stick and a sheet of paper.
ANSWER
Use the mirror to project the image of a distant object onto the sheet of paper.
The distance between the paper and the mirror is approximately equal to the focal length.

 

5.      A concave mirror has a focal length of 25 cm. An object is placed 40 cm from the mirror.
Find the position of the image formed.
State the nature and the magnification of the image.
ANSWER



The nature of the image is real.



6.      A convex mirror has a focal length of 15 cm. An object is placed 5 cm in front of the mirror.
Find the position of the image formed.
State the nature of the image.
ANSWER



The nature of the image is virtual.

7.      In an experiment to find the focal length of a concave mirror the following values were obtained.

u/m

0.24

0.26

0.28

0.30

0.32

0.34

v/m

1.2

0.867

0.70

0.60

0.533

0.486

 

(a)    Draw a labelled diagram of the apparatus used.

(b)   Use a suitable graph to find a value for the focal length of the concave mirror, f.

 

ANSWER
(a) 
                 
(b) 

1/u / m-1

4.2

3.8

3.6

3.3

3.1

2.9

1/v / m-1

0.8

1.2

1.4

1.7

1.9

2.1