Question

An object is placed at distance 10 cm in front of a convex mirror of focal length 20 cm. It's 2/3 times virtual image is formed 20/3 cm behind the mirror.

Answer the following:-

1)The correct value and sign of the object distance in the above question would be

2) The correct value and sign of the image distance in above question would be

3)The correct value and sign of the focal length in above question would be

4)The correct value and sign of the magnification in above question would be

Please answer all

Answer 1

Answer:

ANSWER

It is to be remembered that a convex mirror always forms the virtual, erect and diminished image.

Given: Object distance, u=−10cm Focal length, f=15cm

To find: Image distance, v

From mirror formula :

v

1

+

u

1

=

f

1

v

1

−

10

1

=

15

1

v

1

=

15

1

+

10

1

=

150

25

v=6cm

Hence image will be formed 6 cm beyond the mirror, i.e virtual magnification

m=

u

−v

=

−10

−6

=0.6

Hence it will be erect and diminished

⅝

Answer 2

Given; Focal length, f=20cm

Object distance, u=−10cm

Using mirror formula.

1/v + 1/u= 1/f

1/v = 1/f

1/u -1/20

− 1/−10 (∵u=−10)

= 1/20 + 1/10

=20/3

⇒v= 3/20 cm