Question

Draw the ray diagram of convex lens making image when object is at radius of curvature (2F₁).

1. An object is placed vertically at a distance of 20 cm from a convex lens. If the height of object is 5 cm and focal length of the lens is 10 cm, what will be its position, size and nature of image?
2. Flow much bigger will the image be as compared to the object?

Answer 1

(a) Height of object (h₁) = 5 cm

Focal length (f) = 10 cm

Object distance (u) = −20 cm

Formula: `1/"v" - 1/"u" = 1/"f"`

⇒ `1/10 = 1/"v" - 1/((-20))`

⇒ `1/"v" = 1/20`

⇒ v = 20 cm

And `"h"_2/"h"_1 = "v"/"u"`

⇒ h₂ = `("v" xx "h"_1)/"u"`

= `(20 xx 5)/((-20))`

⇒ h = −5 cm

(b) m = `"v"/"u" = 20/(-20)` = −1

m = −1

The image is real, inverted and of the same size.