SAMPLE ANSWER 12A (i) Distances may be left in cm rather than converting to SI units, therefore
1 f 1
60 1 1 v v 60 The image distance is 60 cm.
(ii) ‘v’ is positive, therefore the image is real. (iii)
magnification
m v u 60
The image height is 8 cm. m
30 2
image height object heightQ2
image height 4 Qimage height 8
image distance object distance
image height object height
u 1
20 1 1
v Q 1 30 1 v 20 1 30 1 v
u 30 cm ; f 20 cm.
SAMPLE PROBLEM 12B
An object, of height 4 cm, is placed 30 cm in front of a convex mirror of focal length 20 cm. (i) What is the distance of the image from the mirror? (ii) What is the nature of the image? (iii) What is the height of the image?
SAMPLE ANSWER 12B (i) Distances may be left in cm rather than converting to SI units, therefore
The mirror is convex, so we use the adjusted formula: u 1
1 f 1
1 v 1
1 v 1
The image distance is 12 cm. 30 1 12
(ii) We are dealing with a convex mirror, therefore the image is virtual. v 12
202 INVESTIGATING PHYSICS 20 v Q 1 20 1 30 1 v
