Question

A 9.0 cm object is 3.0 cm from a lens, which has a focal length of –12.0 cm.

Answer 1

The answers are -2.4 for the distance. 7.2 for the height. Concave for the type

Answer 2

Answer :

Image distance = -2.4 cm

Height of image = 7.2 cm

Concave lens

Explanation :

Given that,

Height of the object, h = 9 cm

Object distance, u = 3 cm

Focal length, f = -12 cm

Using mirror's formula

$\dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v}$

$\dfrac{1}{v}=\dfrac{1}{f}-\dfrac{1}{u}$

$\dfrac{1}{v}=\dfrac{1}{(-12)}-\dfrac{1}{(3)}$

v = -2.4 cm

Image distance is 2.4 cm from the lens.

Magnification, $m =\dfrac{-v}{u}=\dfrac{h'}{h}$

$h'=\dfrac{-vh}{u}$

h' = 7.2 cm

The height of the image is 7.2 cm. This shows that the image is upright.

The lens used is concave lens.