Question

A concave lens has a focal length of 15cm and object is placed 10cm from the len. find the position and nature of the object.​

Answer 1

Given that,

Focal length f=15cm

Distance of the image v=−10cm

We know that,

1/f = 1/v - 1/u

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

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

-1/u = 1/30

u = −30cm

Hence, the object is placed 30 cm away from the concave lens.

Hope this answer helps you out.

Answer 2

Given:-

• Focal length ,f = -15cm

• Object - distance , u = -10cm

To Find:-

• Image - distance ,v .

Solution:-

By using lens formula

• 1/v - 1/u = 1/f

Substitute the value we get

→ 1/v = 1/f + 1/u

→ 1/v = 1/(-15) - 1/(-10)

→ 1/v = -2-3/30

→ 1/v = -5/30

→ 1/v = -1/6

→ v = -6cm

here negative sign show that the image is virtual and formed on the same side of the lens.

∴ The image distance is 6cm.