Question

a lens of focal length 20 cm is placed in air. when an object is placed at a distance of 15 cm from its optical centre the image formed is found to be erect and magnified. a. what what type of lens is this? b. is the image real or virtual​

Answer 1

Explanation:

(i)

u=−20cm and f=15cm

v

1

−

u

1

=

f

1

⟹

v

1

=

20

−1

+

15

1

⟹v=60cm

Magnification is m=

u

v

=−3

Image formed is real, inverted and three times magnified.

(ii)

u=−5cm and f=15cm

v

1

−

u

1

=

f

1

⟹

v

1

=

5

−1

+

15

1

⟹v=−7.5cm

Magnification is m=

u

v

=1.5

Image formed is virtual, erect and 1.5 times magnified.