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Question
An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed.
Solution
Object distance, u = 20 cm
Image distance, v = ?
Focal length, f = 10 cm
As per the sign conventions used,
f = −10 cm
u = −20 cm
According to the lens formula,
`1/f=1/v-1/u`
`1/v=1/f+1/u`
`1/v=1/-10+1/-20=-3/20`
`rArrv=-20/3=-6.6" cm"`
The image is formed at a distance of 6.6 cm from the lens at the same side where the object is placed.
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