Question

An object 40 cm to the right of a lens forms an image 10 cm from the lens on the other side. Find f and the magnification M (which is positive (negative) if the image is upright (inverted).)

Answer 1

Answer:

Object distance u=−30 cm

Focal length of convex lens f=20 cm

Height of object h

o

=4 cm

Using lens formula :

v

1

−

u

1

=

f

1

∴

v

1

−

−30

1

=

20

1

⟹ v=60 cm

Magnification

h

o

h

i

=

u

v

⟹

4

h

i

=

−30

60

⟹ h

i

=−8 cm

Ratio of size of image to that of object =

∣h

o

∣

∣h

i

∣

=

4

8

=2