A convex mirror with a focal length of −20 cm forms an image 12 cm behind the surface.If the object height is 1.2 cm what is the image height?
A) 0.30 cm
B) 0.48 cm
C) 0.94 cm
D) 3.0 cm

Question

Quizplus · Accepted Answer

Using the mirror formula: 1/f = 1/v + 1/u
where f = -20 cm (as it is a convex mirror),
v = -12 cm (since the image is formed 12 cm behind the mirror),
u = ?
Using the sign convention:
Object distance (u) = +6.67 cm
Now, using magnification formula: m = -v/u
where magnification (m) = image height/object height
object height = 1.2 cm
we get image height = -m*object height = 0.48 cm (rounded to two decimal places)
Therefore, the best choice is B.

A Convex Mirror with a Focal Length of −20 Cm