A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

Answer:

Focal length (f ) = -15 cm

Distance of image (v) = -10 cm

\(\frac{1}{v} – \frac{1}{u} = \frac{1}{f}\)

1/u = -(1/10) – (1/- 15)

1/u =1/15 – 1/10

1/u = -0.033

u = -30 cm

so the object is placed 30 cm away from the concave lens.

Ray diagram

 

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