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Light Reflection and Refraction
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24/08/2021 11:54 am
Topic starter
A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. What is the :
(a) power of this combination of lenses?
(b) focal length of this combination of lenses?
1 Answer
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24/08/2021 11:57 am
\(P_1\) = +5D, \(P_2\) = -7.5D
(a) Power of combination:
P = \(P_1\) + \(P_2\)
= +5D + (-7.5D)
= -2.5D
(b) Focal length of the combination:
f = \(\frac{1}{P}\) = \(\frac{1}{-2.5}\)
= -0.4 m = -40 cm