Question

two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other find the focal length of the combination​

Answer 1

Answer:

10 cm

Explanation:

Total focal length= F

focal length 1= f1= 15cm (converging lens has (+ve) focal length)

focal lengt 2 = f2= 30cm

1/F= 1/f1+ 1/f2

    = 1/15 + 1/30

= 2+1/30

=3/30

=1/10

1/F = 1/10

so, F = 10 cm