Question

an object is placed at a distance of 60cm from a concave lens of focal length 30cm.using lens formula and mirror formula find the distance of the image​

Answer 1

GivEn :

• Object distance, u = -60 cm

• Focal length, f = -30 cm [concave lens ]

⋆ NOTE :

For focal length, f in concave lens is always taken as negative. And for object distance, u in concave lens it is taken as negative since image is formed on -X side.

To find :

Distance of the Image formed.

SolutioN :

In order to calculate the object distance (v) we'll use the LENS formula as we're given with the certain values, that is, object distance & focal length.

By using Lens formula :

$:\implies\sf \dfrac{1}{v} - \dfrac{1}{u} = \dfrac{1}{f}$

$:\implies\sf \dfrac{1}{v} - \dfrac{1}{ - 60} = \dfrac{1}{ - 30}$

$:\implies\sf \dfrac{1}{v} = \dfrac{ - 1}{30} - \dfrac{1}{60}$

$:\implies\sf \dfrac{1}{v} = \dfrac{ - 1 \times 2}{30 \times 2} - \dfrac{1}{60}$

$:\implies\sf \dfrac{1}{v} = \dfrac{ - 2}{60} - \dfrac{1}{60}$

$:\implies\sf \dfrac{1}{v} = \dfrac{ - 3}{60}$

$:\implies\sf v= \dfrac{ -60}{3}$

$:\implies\sf { \boxed{ \frak{ \purple{v= - 20 \: cm }}}} \: \bigstar$

$\therefore$ The required image will be formed at 20 cm in front side of the lens.