1.

Two lenses of power`+2.50D`and`-3.75D`are combined to form a compound lens Its focal length in cm,will beA. 40B. -40C. -80D. 160

Answer» Correct Answer - 3
`P=P_(1)+P_(2)`
`P=2.50-3.75=-1.25D`
`:.f=(1)/(P)`
or`f=(1)/((-1.25))=-0.8m`
`f=-80cm`


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