Question

At what distance from a concave mirror of focal length 10 cm should an object be placed so that :
(a) its real image is formed 20 cm from the mirror ?
(b) its virtual image is formed 20 cm from the mirror?​

Answer 1

Answer:

(a) f=10cm

v=20cm (real image)

v

1

+

u

1

=

f

1

−20

1

+

u

1

=

−10

1

u

1

=

10

−1

+

20

−1

=

20

−1

u=−20cm

(b)f=10cm

v=20cm (virtual image)

v

1

+

u

1

=

f

1

20

1

+

u

1

=

−10

1

u

1

=

10

−1

+

20

−1

=

20

−3

u=−

3

20

cm