UPSC CDS 2 2020 GK Paper

Object distance, u=−40cm
Focal length, f=25cm
Let v be the image distance.
From lens formula,
‌

1

f

‌‌=‌

1

v

−‌

1

u

⇒‌

1

v

‌‌=‌

1

f

+‌

1

u

=‌

1

25

+‌

1

(−40)

⇒‌

1

v

=‌

1

25

−‌

1

40

=‌

8−5

200

=‌

3

200

⇒v=‌

200

3

=66.7cm
Now, magnification produced by lens,
m=‌

v

u

=‌

66.7

(−40)

=−1.66
Since, the magnification is negative, so the image formed will be real and inverted.
Also, the magnitude of magnification is greater than unity, so the image will be magnified.