Question

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in dipoters of the combination is:-

Answer 1

Focal length of convex lens = 25 cm

So, the power(P1) of lens:

P = 1/f(m) = 100/f(cm)

Since f is in 'cm'

P = 100/f = 100/25 = +4D

Similarly,

Focal length of concave lens= -25 cm

So, power(P2) = 100/f

= 100/(-25)

= -4D

Now, total power of lenses in combination is the ALGEBRAIC SUM OF POWERS OF EACH INDIVIDUAL LENS IN THE COMBINATION.

Here, P(total) = P1+P2

= +4D + -4D

= 4D - 4D

=> 0 D

Hence, the power of combination is 0 dioptre, i.e. , it will act as a plane lens.

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Answer 2

Answer:

0 D

Explanation:

because power of both are equal but in opposite sign so the combination acts as plane mirror