Question

The image of an object formed by a mirror is real, inverted and is of magnification -1. If the image is at the distance
of 30 cm from the mirror, where is the object placed? Find the position of the image if the object is now moved 20 cm
towards the mirror. What is the nature of the image obtained? Justify your answer with the help of a ray diagram.

Answer 1

Since the magnification is -1 the image is of the same size as that of the object.

Therefore we can say that it at Centre of curvature. The object is also at COC and image also at COC.

Image distance= 30 cm Object distance = 30

focal lenght = 30/2 = 15

if it moved 20 cm then object distance = 10cm

Nature:

object : Between F and O

Image :

• Virtual
• Erect
• Magnified

Answer 2

Answer:

+ 30 cm

Explanation:

Given :

Magnification = - 1

Image distance = 30 cm

We know

m = - v / u

- 1 = 30 / u

u = - 30 cm

Now we have ,

1 / f = 1 / v + 1 / u

1 /  f = 1 / - 30 - 1 / 30

f = - 15 cm

When object moved 20 cm

u' = - 30 + 20 = - 10 cm

We have f = - 15 cm

We have to find new image distance v'

Again ,

1 / f = 1 / v' + 1 / u'

- 1 / 15 = 1 / v' - 1 / 10

1 / v' = 1 / 30

v' = 30.

Nature of image as :

Virtual

Erect

Magnified.