Question

A convex lens of focal length 20cm is placed at a distance of 40cm from a wall.
At what distance from the lens should a candle be placed so that it's image is formed on the wall? Draw a ray diagram to show the image formation.

Class10

Answer 1

Answer:

Focal length=f=10cm

Image distance=v=20cm

Using sign convention,

f is positive,v is also positive

Lens formula,

1/f=1/v-1/u

1/10=1/20–1/u

1/u=1/20–1/10

1/u=(10–20)/200

1/u=-10/200

u=-20

Object distance=20cm(minus indicates that the lens is converging lens)

hi=height of image and ho=height of object

hi/ho=-v/u

hi/2=-20/20

hi=2cm

hope it helps you✌✌✌