Question

an object is height 6cm is kept in front of the convex lens at a distance of 24cm a real image is formed at a distance of 18cm find the focul length of the lens and height of the image​

Answer 1

Given :

Height of object = 6cm

Distance of object = 24cm

Distance of image = 18cm

Type of lens : convex

To Find :

Focal length and height of the image.

Solution :

❖ Focal length of convex lens is taken positive and that of concave lens is taken negative.

• Focal length of lens can be calculated by using lens formula$.$

➙ 1/v - 1/u = 1/f

➙ 1/18 - 1/(-24) = 1/f

➙ 1/18 + 1/24 = 1/f

➙ (8 + 6) / 144 = 1/f

➙ f = 144/14

➙ f = 10.28 cm

❖ Height of the image :

➛ m = v/u = h'/h

• h' : height of image
• h : height of object

➛ 18/(-24) = h'/6

➛ h' = 6 × 18/(-24)

➛ h' = -18/4

➛ h' = -4.5 cm

• Negative sign shows that image is real and inverted.