Question

An object of length 6 cm is placed on the principal axis of a concave mirror of focal length f at a distance of 4f. The length of image will be-
1. 2 cm
2. 1 cm
3. 1.2 cm
4. 6 cm

Answer 1

Correct Answer - Option 1 : 2 cm

CONCEPT:

The magnification (m) produced by a spherical mirror is given by:

m = I/O 

Where I = height of the image, O = height of the object

The Magnification (m) in terms of focal length (f) and image distance (u) is given by:

\(m=\frac{f}{f-u}\)

CALCULATION:

O = 6 cm

f = - f

u = - 4f

\(\frac{I}{6}=\frac{-f}{-f-(-4f)}\)

I = - 2 cm

So, the length of an image formed is 2 cm