Question

A 3.5-cm-high object is placed at a distance of 12 cm
from a concave lens of focal length 16 cm. Find the
size of the image.
​

Answer 1

Given:-

• Object height (ho) = 3.5 cm

• Object Distance (u) = 12cm

• Focal length (f) = -16cm

To Find:-

• Size of the image (he)

Solution:-

By using lens Formula

⟹ 1/v-1/u = 1/f

Put the value,we get

⟹ 1/v - 1/12 = 1/(-16)

⟹ 1/v = -1/16 -1/12

⟹ 1/v = - 7/48

⟹ v = -48/7 cm

As we know that

⟹ magnification = v/u = he/ho

⟹ m = v/u = he/ho

Put the value we get

⟹ m = -48/7/(-12) = he/3.5

⟹ 4/7 = he/3.5

⟹ 4×3.5/7 = he

⟹he = 2cm

∴ The size of the image is 2cm.