Question

the focal length of of a convex lens is 50 cm if an object is kept at a distance of 75 cm from the lens then find the image distance and magnification produced by the lens ​

Answer 1

Answer:

Magnification is-0.4

v is 30cm

Explanation:

f=+50cm

u=-75cm

By lens formula,

1/f=1/v-1/u

1/v=1/f+1/u

=1/50-(-75)

=1/50+1/75

=3+2/150

=5/150

=1/30

so,

v=30cm

M=v/u

=30/-75

=-2/5

=(-0.4)

Answer 2

Answer:

We can use Gaussian equation for thin lens with Cartesian sign convention . 1/f = 1/v - 1/ u

Here, object distance, u = -30 cm.

Focal length , f= 50 cm.

Image distance, v = ?

Thus, 1/50= 1/v -(-1/u) OR

1/50 - 1/30 = 1/v OR

v= - 75 cm.

The image is on the side of object and is erect and virtual . The magnification , m is positive. See figure.