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### Course: Class 10 Physics (India)>Unit 1

Lesson 14: Dioptres & power of a lens

# Power of lens

Power is an incredibly useful quantity when it comes to lenses. Let's find out what it is and where it is used.  Created by Mahesh Shenoy.

## Want to join the conversation?

• At @ how did we get it as "14", would really appreciate it if someone can explain it
• We already know that: P=1/f
Given: P = 1/7 m^-1
By diving 1 from 7 we will get:
P = 0.14 m
P = 14 cm
PS: Here we have just converted m into cm i.e. multiplying 0.14 from 100.
• At He says that if 2 lenses are combined,their powers get added up. So if suppose we have a concave and a convex lens, say of -5D and +2D, will their combined powers be equal to -3D and will the nature of this combination be concave lens??
• Yes, you got it right! the nature of the combination of these lenses will be concave.
• In combination of power of lenses, why do we not consider the distances between the optical centres of the given lenses? Is there any formula taking that into account?