1.

Two convex lenses of focal lengths 25 cm and 15 cm are placed in contact with each other. Find the focal length of combination.

Answer»


Solution :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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