1.

An object placed `10 cm` in front of a lens has an image `20 cm` behind the lens. What is the power of the lens`(` in dioptres `)` ?A. `1.5`B. `3.0`C. `-15.0`D. `+15.0`

Answer» Correct Answer - D
`u=-10cm, v=20cm`
`(1)/(f)=(1)/(v)-(1)/(u)=-(1)/(20)-((-1)/(10))=(3)/(20)impliesf=(20)/(3)cm`
Now, `F=(100)/(f)=(100)/(20//3)=+15D`


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