Question

Apply lens formula to determine the focal length of a convex lens which forms a three times magnified real image of an object placed 16 cm in front of it

Answer 1

Given data:

f=?

u=16

v=?

Let object height be x

Image height=3x

3x/x=v/u

3x/x=v/16

3=v/16

3*16=v

48=v

Lens formula:

1/v-(-1/u)=1/f

1/v+1/u=1/f

1/16+1/48=1/f

1*3/16*3+1/48=1/f

3/48+1/48=1/f

4/48=1/f

48/4=f

12=f

focal length=12