Question

A concave lens of focal length 25cm and a convex lens of focal length 20cm are placed in contact with each other what is the power of this combination? Also calculate focal length of the combination.

Answer 1

hey i hope the power is 45

Answer 2

ANSWERS :-


$solution$

HERE,

focal length of concave lens f1 = -25cm,

power of the combination, p = ?

focal length of convex lens, f2 = +20 cm

focal length of the combination, F = ?


P1 = 100/f1(cm)

p1 = 100/-25

P1 = -4 dioptre

and

P2 = 100/f2(cm)

= 100/20

= +5 dioptre

As

p = P1 + P2 ,

p = -4 + 5

p = 1 dioptre

Thus,

F = 100/p = 100/1 = 100cm = 1m.

⚡⚡positive sign of P and F indicate diet the combination of two given lenses behave as a convex lens.

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