Question

pls solve these questions with solutions..
I will mark you as brainliest.​

Answer 1

answer no. 11
option no.a will be correct
$\frac{1}{ F } = \frac{2}{f} + \frac{1}{f_{m} }$
here
$f_{m} = \infty$
$hence F \: = \frac{f}{2} = \frac{20}{2} = 10$
answer 12.
option no.a will be correct

solution
u=-25cm
v= +75cm
=>
$\frac{1}{f} = \frac{1}{ + 75cm} - \frac{1}{ - 25cm}$
$\frac{1}{f} = + 18.75cm$

answer 13.

m=vu

=h'h

So  

 v-u=-8h -----1

and   

-uv=-2h

or      

-vu=h-2 -----2

from eqns 1 and 2      

   -8h=h2or 

    h2=16

or     

      h=4cm

So the height of the object is 4cm.


answer no.14