Question

a concave lense of focal length 15 cm from an image 10 cm from the lens .how far is an object is placed from the lens ? draw a ray diagrams

Answer 1

Focal length of concave lens (OF1), f = −15 cm

Image distance, v = −10 cm

According to the lens formula,

Given f = -15 cm. v= -10 cm, u = ?

Lens formula 1/f = 1/v- 1/u

1/-15 = 1/-10 - 1/u

1/u = -1/10 + 1/15 = -3 +2 /30 = -1/30

u = -30 cm

So the object should be placed 30 cm from the lens.



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