Question

a convex lens produces an inverted image magnified three times of an object placed at a 15cm from it. calculate the focal length of the lens.​

Answer 1

Answer:

Focal length of lens is +11.25 cm.

Step-by-step explanation-

Given:

• m ( magnification ) = -3

[ Since the image is inverted, magnification will be -3]

• u ( object distance ) = -15cm

To find:

• focal length = ?

____..

We know that

${\boxed {\huge {\tt m= \frac{v}{u}}}}$

Where,

• m is magnification
• v is image distance
• u is object distance

$\tt {\implies - 3 = \frac{v}{ - 15}}$

$\tt {\implies v = ( - 3 )\times ( - 15)}$

$\tt\blue {\implies v = 45cm}$

Now, according to lens formula-

${\boxed {\huge {\tt \frac{1}{v} - \frac{1}{u} = \frac{1}{f}}}}$

Substituting values-

$\tt { \longrightarrow \frac{1}{45} - \frac{1}{ -15} = \frac{1}{f} }$

$\tt { \longrightarrow \frac{1 + 3}{45} = \frac{1}{f}}$

$\tt { \longrightarrow \frac{4}{45} = \frac{1}{f}}$

$\tt\red { \longrightarrow f = \frac{45}{4}}$

[ After reciprocating both sides]

$\tt\red { \longrightarrow f = 11.25}$

Hence, the focal length of the lens is 11.25 cm.

Answer 2

Answer:

Your ans. is 11.25

I HOPE IT IS HELPFUL FOR YOU