Question

Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose.

1. State the nature of the lens and reason for its use.
2. Where should the palmist place/hold the lens so as to have a real and magnified image of an object?
3. If the focal length of this lens is 10 cm and the lens is hold at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.

Answer 1

(i) Because it creates a magnified image of the palm, the type of lens utilised is a convex lens. 

(ii) When an object is positioned between the lens’s center of curvature and focus, a convex lens can provide a real and enlarged picture of the object.

(iii) Given, f = +10 cm

u = –5 cm

v = ?

By lens formula, `1/f=1/v-1/u`

`1/10=1/v-(-1/5)`

`1/v=1/10-1/5`

`1/v=(-1)/10`

v = –10 cm

By using magnification formula, m = `v/u`

m = `(-10)/-5`

m = 2 cm

Image is formed twice the size of the object.