Question

.A concave lens of focal length 15 cm. form an image 10 cm. fron
the lens. How far is the object placed from the lens?​

Answer 1

Explanation:

f = -15 cm

v = -10 cm

Lens formula: 1/v – 1/u =1/f

1/-10 – 1/u = 1/-15

1/u = - (1/10) + 1/15

1/u = -2/60

u = -30 cm

Object is at 30 cm from the concave lens (on left side).

Here, OB = 30 cm

OF = 15 cm

OB’ = 10 cm

Answer 2

Answer:

Focal length (f ) = -15 cm

Distance of image (v) = -10 cm

1v–1u=1f

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.