# If each two concave lenses of focal length 30 cm are kept in contact with each other what will be the power of combination? - Science and Technology 1

Numerical

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.

Concept: Combination of Lenses
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