Question

An object is placed at a distance of 20 cm from a convex lense of focal lenght 20 cm .At what distance is the image formed from the lens ? Also find magnification of the image​

Answer 1

Answer:

v= 10 cm and m = 0.5 cm

Explanation:

Using the lens formula and magnification , we can find the image distance and magnification of the image. For detailed solution please refer the given picture .

Answer 2

Given :

In convex lens,

Object distance : - 20 cm

Focal length : 20 cm

To find :

The position of the image and the magnification of the image.

Solution :

Using lens formula that is,

» The formula which gives the relationship between image distance, object distance and focal length of a lens is known as the lens formula.

The lens formula can be written as :

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

where,

• v denotes image distance
• u denotes object distance
• f denotes focal length

by substituting all the given values in the formula,

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

$\dashrightarrow \sf \dfrac{1}{v} - \dfrac{1}{ - 20}= \dfrac{1}{20}$

$\dashrightarrow \sf \dfrac{1}{v} + \dfrac{1}{20}= \dfrac{1}{20}$

$\dashrightarrow \sf \dfrac{1}{v} = \dfrac{1}{20} - \dfrac{1}{20}$

$\dashrightarrow \sf \dfrac{1}{v} = \dfrac{1 - 1}{20}$

$\dashrightarrow \sf \dfrac{1}{v} = \dfrac{0}{20}$

$\dashrightarrow \sf v = \infty$

If the object distance equals the focal length then the image is at infinity