Question

An object of height 2 cm is placed at a distances of 15 cm in front of a concave lens of power -10 dioptre. find the size of the image​

Answer 1

Given :

Height of object = 2cm

Distance of object = 15cm

Power of lens = -10D

Type of lens : concave

To Find :

Size of the image.

Solution :

❖ First of all we need to find focal length of the lens. We know that,

$\dag\:\underline{\boxed{\bf{\orange{Power=\dfrac{1}{Focal\:Length}}}}$

➙ P = 1 / f

➙ -10 = 1 / f

➙ f = -0.1 m = -10 cm

♦ Distance of image can be calculated by using lens formula.

➙ 1/v - 1/u = 1/f

➙ 1/v - 1/(-15) = 1/(-10)

➙ 1/v = -1/10 - 1/15

➙ 1/v = (-3 - 2) / 30

➙ v = -30/5

➙ v = -6 cm

♦ Size of the image :

➠ m = v/u = h'/h

• h' denotes size of image
• h denotes size of object

➠ (-6)/(-15) = h'/2

➠ h' = 12/15

➠ h' = 0.8 cm