1.

An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens . What is the focal length and power of the lens ? Is it is converging lens or diverging lens ?

Answer»

SOLUTION :Data : `u=-60 cm, v=-20 cm, f=?`
`1/f =1/v -1/u =(1)/(-20 cm)-(1)/(-60 cm)`
`=-((1)/(20 cm)-(1)/(60cm))=-((3-1)/(60cm))`
`=-(2)/(60cm)=-(1)/(30cm)`
`therefore ` The focal length of the LENS , f=-30 cm. As f is NEGATIVE , it is diverging lens.


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