Question

Two thin lenses of foccal length 15cm and 30cm respectively are kept in contact with each other. What is the power of combined system

Answer 1

Answer:

let f1= 15cm and f2 = 30cm

power of lens = 1/f

p= 1/f1+1/f2

p= 1/15 +1/30

p= 2+1/30

p= 1/10

Answer 2

Answer:

Focal length of the combination = 10 cm

Explanation:

Focal length of two thin lenses kept in contact is given by

f1 × f2

F = ---------------

f1 + f2

where f1 focal length of one lens and

f2 focal length of otther lens

therefore

Focal length of the combination

15 × 30

F = ---------------

15 + 30

450

= -----------

45

= 10 cm