Question

question number 21. tell me
CLASS 10th​

Answer 1

In the first case , we can say that :

$- \dfrac{v}{u} = \dfrac{1}{2}$

$= > - \dfrac{v}{( - 60)} = \dfrac{1}{2}$

$= > v = 30 \: cm$

So applying Mirror formula , we get :

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

$= > \dfrac{1}{f} = \dfrac{1}{30} + \dfrac{1}{( - 60)}$

$= > \dfrac{1}{f} = \dfrac{1}{30} - \dfrac{1}{60}$

$= > \dfrac{1}{f} = \dfrac{2 - 1}{60}$

$= > \dfrac{1}{f} = \dfrac{ 1}{60}$

$= > f = 60 \: cm$

In the 2nd case , we see :

$- \dfrac{v}{u} = \dfrac{1}{3}$

$= > v = - \dfrac{u}{3}$

Now again applying Mirror formula ,

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

$= > \dfrac{1}{60} = - \dfrac{3}{u} + \dfrac{1}{u}$

$= > \dfrac{1}{60} = \dfrac{ - 3 + 1}{u}$

$= > \dfrac{1}{60} = \dfrac{ -2}{u}$

$= > u = - 120 \: cm$

So final answer is :

Object distance has to be 120 cm

Answer 2

Answer:

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