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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:
C
Power of combination is given by
`P=P_1+P_2=(-15+15)D=-10D`
Now, `P=(1)/(f)impliesf=(1)/(P)=(1)/(-10)` metre
`:'``f=-((1)/(10)xx100)cm=-10`cm
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