Question

an object 4cm in front of a converging lens produces a real image 12cm
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Answer 1

Explanation:

Focal length =f=20cm

object distance =−u

image distance =v

magnification =m=−10 [- sign is used because the image is real since it is obtained on screen]

we know,m=v/−u

−10=v/−u

10u=v

using$$,$4 

1/f=1/v−1/−u

1/20=1/10u+1/u

1/20=1+10/10u

10u/20=11

u=22cm

therefore, the object distance is 22cm