A concave lens has a focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens?

CONCEPT:

Lens: The transparent curved surface which is used to refract the light and make an image of any object placed in front of it is called a lens.

Concave lens: It is thin in the middle and thick at the edges.

Actually, a concave lens is a spherical lens whose two surfaces are concave or bent inward.

A concave lens is also know known as the ​diverging lens.

Lens formula is given by:

\(\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\)

The magnification of the lens is given by:

Magnification (m) = v/u

Where u is object distance, v is image distance and f is the focal length of the lens

CALCULATION:

Given - focal length (f) = -15 cm and image distance (v) = -10 cm

Lens formula is given by:

\(⇒ \frac{1}{v} - \frac{1}{u} = \frac{1}{f}\)

\(⇒ \frac{1}{u} = \frac{1}{v}-\frac{1}{f}\)

\(⇒ \frac{1}{u} =\frac{1}{{ - 10}} - \left( {\frac{1}{{ - 15}}} \right)=\frac{-1}{10}+\frac{1}{15}=\frac{-3+2}{30}=\frac{-1}{30}\)

⇒ u = -30 cm

Object distance from the lens is 30 cm.