Question

an object placed at 60 cm from a concace lence of focal length 30,cm fund the imge distance​

Answer 1

Correct Question  :-

An object placed at a distance of  60 cm from a concave lens  of focal length 30cm find the image distance​

Given :-

• Object distance = - 60 cm
• Focal length = - 30 cm

Note :

• Object distance is negative as distances are measured from the pole of the mirror
• Focal length of a concave lens is always negative

To find :-

• image distance

How to solve :-

• As the values of object  distance(u) and focal length (f) are already known to us we can simply substitute these values in the lens formula in order to find image distance (v)

Solution :-

By using the lens formula ,

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

here ,

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

Now let's substitute the given value's in the above equation ,

$\longrightarrow{\mathtt{ \dfrac{-1}{30} = \dfrac{1}{v} + \dfrac{1}{60} }}$

$\longrightarrow{\mathtt{ \dfrac{1}{v} = \dfrac{1}{60} +\dfrac{1}{30}}}$

$\longrightarrow{\mathtt{ \dfrac{1}{v} = \dfrac{1+2}{60} }}$

$\longrightarrow{\mathtt{ \dfrac{1}{v} = \dfrac{3}{60} }}$

$\longrightarrow{\mathtt{ \dfrac{1}{v} = \dfrac{1}{20} }}$

$\longrightarrow{\mathtt{ v = 20 cm }}$

The image is formed at a distance of 20 cm behind the mirror