Question

answer the question
A convex mirror forms the image of an object placed at a distance 80 cm in front of mirror at a distance of 40 cm .find its focal length. ​

Answer 1

Given :

In convex mirror,

Object distance = -80 cm

Image distance = 40 cm

To find :

The focal length of the mirror

Solution :

Using mirror formula that is,

» A formula which gives the relationship between image distance, object distance and focal length of a sperical mirror is known as the mirror formula .i.e.,

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

where,

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

By substituting all the given values in the formula,

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

$\dashrightarrow\sf \dfrac{1}{40} + \dfrac{1}{( - 80)} = \dfrac{1}{f}$

$\dashrightarrow\sf \dfrac{1}{40} - \dfrac{1}{80} = \dfrac{1}{f}$

$\dashrightarrow\sf \dfrac{2 - 1}{80} = \dfrac{1}{f}$

$\dashrightarrow\sf \dfrac{1}{80} = \dfrac{1}{f}$

$\dashrightarrow \underline{ \boxed{\sf f = 80 \: cm}}$

Thus, focal length of the image is 80cm.

Answer 2

Answer:

In convex mirror,

Object distance = -80 cm

Image distance = 40 cm

To find :

The focal length of the mirror

Solution :

Using mirror formula that is,

» A formula which gives the relationship between image distance, object distance and focal length of a sperical mirror is known as the mirror formula .i.e.,

1/v + 1/u = 1/f

where,

v denotes Image distance

u denotes object distance

f denotes focal length

By substituting all the given values in the formula,

equation in the attachment!!