Question

The lens forms the real image 3 times the size of the object at 20cm from the lens. The focal length will be​

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12th

Physics

Ray Optics and Optical Instruments

Combination of Mirror and Lenses

A convex lens of focal leng...

PHYSICS

A convex lens of focal length 20 em produces a real image twice the size of the object. Then the distance ofthe object from the lens is

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ANSWER

Given f = 20 cm, h

1

=2h

0

⇒

h

0

h

1

=m=2

∴

u

v

=2⇒v=2u

∴

v

1

−

u

1

=

f

1

(lens formula)

⇒

2u

1

−

−u

1

=

20

1

⇒

2u

1+2

=

20

1

⇒

2u

3

=

20

1

⇒ u = 30 cm