Question

Good Evening Friends !!

Q- A convex lens produces an inverted image magnified three times of an object placed at a distance of 15cm from it. Calculate focal length of the lens.

CLASS - X
PHYSICS
CH- LIGHT

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Answer 1

Hey user !

Here's the answer :

Answer : 11.25 cm

Step-by-step explanation :

${ \underline {\sf{Given :-}}}$

u = - 15 cm

Image is inverted , so

Magnification (m) = -3

Use magnification formula,

$\sf{ m = \frac{v}{u} = - 3}$

$\sf{ \frac{ v}{ - 15} = - 3}$

$\sf{v = 45 \: cm}$

Now,

$\sf{ \frac{1}{v} - \frac{1}{u} = \frac{1}{f}}$

$\sf{ \frac{1}{45} - \frac{1}{ - 15} = \frac{1}{f}}$

$\sf{ \frac{1}{f} = \frac{ - 1 - 3}{ 45} }$

$\sf{ \frac{1}{f} = \frac{ - 4}{45}}$

$\sf{ \frac{1}{f} = \frac{-1}{11.25}}$

$\sf{{f} = 11.25 \: cm}$

Thanks!!

Answer 2

$\huge{ \pink{ \bold{ \boxed{ \ulcorner{ \star \: answer \: \star}{ \ulcorner}}}}}$
According to the question.......

Magnification of convex lens is always negative ( - ).

So,
$m = - 3$