Question

two lenses of power 1.5 D plus 1 D are placed in contact then the effective power of combination will be

Answer 1

For combination of lenses, the power of each lens is added to get the resultant power.


P = P1 + P2


   = +3.5 – 2.5


   = 1 D


Now, f (in m) = 1/P (in D)


So, f = 1/1 = 1 m = 100 cm

Answer 2

The effective power of combination is 2.5 D.

Explanation:

Power of lens 1, $P_1=1.5\ D$

Power of lens 2, $P_2=1\ D$

We need to find the effective power of combination. The effective power of combination of two lenses is given by :

$P=P_1+P_2$

P = 1.5 + 1

P = 2.5 D

So, the effective power of combination is 2.5 D.

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Effective power of combination

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