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Question
If each two concave lenses of focal length 30 cm are kept in contact with each other what will be the power of combination?
Solution
Given: f1 = f2 = – 30 cm = – 0.3 m
To find: Power of combination (P)
Formula: P = `1/"f" = 1/"f"_1 + 1/"f"_2`
Calculation: From formula,
P = `1/(- 0.3) + 1/(- 0.3)`
`= (- 10)/3 + (- 10)/3`
`= (- 20)/3` = - 6.7 D
Power of combination is – 6.7 D.
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