Question

53332 3
333 nm
&
36. A needle placed 45cm from the
placed 980 cm on the other side
of the lens. Identify the type of
the less a determine its focal length
obpect
distance, u=-45cm
Imore destonor = 90 cm
o​

Answer 1

Explanation:

Here, u = -45 cm, v = 90 cm

∴

f

1

=

v

1

−

u

1

=

90

1

+

45

1

=

30

1

⇒f=30cm

when the needle is move 5 cm away from the lens,

u=-(45 + 5) = -50 cm

∴

v

′

1

=

f

1

+

u

′

1

=

30

1

+

(−50)

1

=

150

2

=⇒v

′

=75cm

∴ Displacement of image = v-v' =90-75= 15 cm, towards the lens