Question

30
17. An object is put at a distance 25 cm from the optical centre of a convex lens. If its real image is
formed at a distance 30 cm from the lens then its focal length is about
(1) 10 cm
(2) 14 cm


(3) 12 cm

(4) 20 cm
Answering with explanation or will be reported

Answer 1

Answer:

Explanation:

v

1

​

−  

u

1

​

=  

f

1

​

 

v

1

​

−  

−15

1

​

=  

f

1

​

 

or  

v

1

​

=  

−15

1

​

+  

10

1

​

 or  

v

1

​

=  

30

−2+3

​

 

or v=30 cm.