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Two lenses of power -15D and +5 D are in...

Two lenses of power `-15D` and `+5 D` are in contact with each other. The focal length of the combination is

A

`+10cm`

B

`-20cm`

C

`-10cm`

D

`+20cm`

Text Solution

Verified by Experts

The correct Answer is:
1
Power of a lens is reciprocal of its local length .Power of combined lens is `
P=P_(1)+P_(2)`
`=15+5=-10D`
`:.f=(1)/(p)=(100)/(-10)cm`
or`f=-10cm`
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