Question

A convex lens forms a virtual image when an object is placed at a distance of 20cm from it. The focal length is _________. A. f = 40 cm B. f = 20 cm C. f > 20 cm D. f < 20 cm​

Answer 1

Answer:

Correct option is

D

10cm away from the lens

Given, u=−20 cm ; v=+20 cm

From lens formula,

v

1

−

u

1

=

f

1

20

1

−

20

−1

=

f

1

f=+10 cm

Now object is moved by 5 cm towards the lens

So now, u=−15 cm ; f=+10 cm

v

1

−

u

1

=

f

1

v

1

+

15

1

=

10

1

v=+30 cm

So the image has moved (30−20)=10 cm

Image is moved 10 cm away from the lens.

option D is correct

Answer 2

area factors

Explanation:

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