The plano-convex lens of focal length `20cm` and `30cm` are placed together to form a double convex lens. The final length will beA. `12cm`B. `60cm`C. `20cm`D. `30cm`

The plano-convex lens of focal length `20cm` and `30cm` are placed tog

1.	The plano-convex lens of focal length `20cm` and `30cm` are placed together to form a double convex lens. The final length will beA. `12cm`B. `60cm`C. `20cm`D. `30cm`
Answer» (a) Equivalent focal length `1/F=1/(f_(1))+1/(f_(2))=1/20+1/30` `F=(20xx30)/(20+30)=600/50=12cm`

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The plano-convex lens of focal length `20cm` and `30cm` are placed together to form a double convex lens. The final length will beA. `12cm`B. `60cm`C. `20cm`D. `30cm`

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