Two lenses of power `-15D` and `+5 D` are in contact with each other. The focal length of the combination isA. `+10cm`B. `-20cm`C. `-10cm`D. `+20cm`

Two lenses of power `-15D` and `+5 D` are in contact with each other.

1.	Two lenses of power `-15D` and `+5 D` are in contact with each other. The focal length of the combination isA. `+10cm`B. `-20cm`C. `-10cm`D. `+20cm`
Answer» Correct Answer - 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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Two lenses of power `-15D` and `+5 D` are in contact with each other. The focal length of the combination isA. `+10cm`B. `-20cm`C. `-10cm`D. `+20cm`

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