1.

The focal length of a camera lens is 20 cm. find how far away from the film must the lens ve set in order to photograph an object located at a distance 100 cm from the lesn .

Answer»

Solution :GIVEN: Focal length = 20 cm
(covex LENS )
Object DISTANCE = 100 cm
To find: Image distance (v)
Solution : `1/v - 1/u = 1/f `
`1/v - 1/((-100)) = 1/20`
`1/v + 1/100 = 1/20 `
`1/v = 1/20 - 1/100`
` 1/v = (5-1)/(100)`
`1/v = 4/100`
`1/v = 1/25`
`therefore` Image distance (v) = 25 cm.


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