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Two thin converging lenses of focal leng...

Two thin converging lenses of focal length 15 cm and 30 cm are held in contact with each other. The focal length of the combination is

Text Solution

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The correct Answer is:
Focal length of combination is 9.375 cm.
Given: `f_(1)=25 cm, f_(2)=15 cm`
To find: Focal length of combination (f)
Formula: `(1)/(f)=(1)/(f_(1))+(1)/(f_(2))`
Calculation: From formula,
`(1)/(f)=(1)/(25)+(1)/(15)=(3)/(75)+(5)/(75)=(8)/(75)`
`therefore" "f=(75)/(8)=9.375 cm`
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