Question

a 2cm high object is placed at a distance of 12cm in front of a convex lens of focal length 20cm. find the position and size of the image​

Answer 1

EXPLANATION.

Height of an object = 2 cm.

Placed at a distance of 12 cm in front of convex lens.

Focal length = 20 cm.

As we know that,

Lens formula :

⇒ 1/v - 1/u = 1/f.

Using this formula in this question, we get.

Distance of an object (u) = - 12 cm.

Focal length (f) = 20 cm.

⇒ 1/v - (1/-12) = 1/20.

⇒ (1/v) + (1/12) = (1/20).

⇒ (1/v) = (1/20) - (1/12).

⇒ (1/v) = (3 - 5)/(60).

⇒ (1/v) = (-2/60).

⇒ (1/v) = (-1/30).

⇒ v = - 30 cm.

∴ Image is formed at distance 30 cm on same side of object.

Magnification = (Height of image)/(Height of object) = (Image distance)/(Object distance).

(Height of image)/(2) = (-30/-12).

(Height of image)/(2) = 30/12.

Height of image = (2 x 30)/(12).

Height of image = 5 cm.

∴ Size of the image is 5 cm.