Question

An object of 5cm in size is placed at a distance of 20cm from a concave mirror of focal length

15cm at what distance from the mirror, should a screen be placed to get the sharp image,

also calculate size of the image​

Answer 1

Answer:

Height of image (h2) =?

Height of object (h1) = 5cm

Focal length of mirror(f)=-15cm

Object distance (u)=--20cm

Image distance(v)=?

Now we will apply mirror formulae

1/f=1/v+1/u

-1/15=1/v-1/20

shifting -1/20 to r.h.s

1/20-1/15=1/v

1/v=-1/60

v=-60

Therefore image will be formed at 60 cm in front of mirror

Now, we will calculate magnification.

Since we have two formulas for magnification w will use both the formulas to calculate height of the image.

magnification(m)=-v/u=-(-60/-20)=-3

magnification(m)=h2/h1

                    -3=h2/5

                     -15=h2

                      h2=-15

Therefore size of image will be 12cm in size/height and since size is in negative image will be formed below principal axis.