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प्रश्न
A camera fitted with a lens of focal length 50 mm is being used to photograph a flower that is 5 cm in diameter. The flower is placed 20 cm in front of the camera lens.
At what distance from the film should the lens be adjusted to obtain a sharp image of the flower?
उत्तर
Given:
Focal length, f = 50 mm = 5 cm
Object distance, u =-20 cm
Image distance, v = ?
Putting these values in lens formula, we get:
⇒`1/v-1/u=1/f`
⇒`1/v-1/-20=1/5`
⇒`1/v+1/20=1/5`
⇒`1/v=1/5-1/20`
⇒`1/v=(20-5)/100`
⇒`1/v=15/100`
⇒`v=20/3`
⇒`v=6.66` cm
Film should be adjusted at a distance of 6.66 cm behind the lens.
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(b) How does the size of image change?
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