Question

Kumar conducts an experiment using a concave lens with focal length of

20 cm. He places an object at a distance of 30 cm in front of the lens.

Where is the image most likely to form? Draw a suitable ray diagram to

prove your answer.​
pls answer itfast comeone​

Answer 1

Given:

Kumar conducts an experiment using a concave lens with focal length of 20 cm. He places an object at a distance of 30 cm in front of the lens.

To find:

• Image distance

• Ray diagram

Calculation:

Applying Lens Formula with appropriate sign convention:

$\rm{ \therefore \: \dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u} }$

$\rm{ = > \: \dfrac{1}{( - 20)} = \dfrac{1}{v} - \dfrac{1}{( - 30)} }$

$\rm{ = > \: - \dfrac{1}{20} = \dfrac{1}{v} + \dfrac{1}{30} }$

$\rm{ = > \: \dfrac{1}{v} = - \dfrac{1}{20} - \dfrac{1}{30}}$

$\rm{ = > \: \dfrac{1}{v} = \dfrac{ - 3 - 2 }{60} }$

$\rm{ = > \: \dfrac{1}{v} = \dfrac{ - 5 }{60} }$

$\rm{ = > v = - 12 \: cm}$

So , final answer is:

$\boxed{ \large{ \bf{ v = - 12 \: cm}}}$

Important Point:

• Irrespective of object distance, the image will always be formed in between the focus and the optical centre of lens.

Hope It Helps.

Answer 2

Answer: v = -12cm (Image formed in front of lens)

Concept: The relation between object distance, image distance and focal length of lens is given by lens formula

Lens Formula    1/f = 1/v - 1/u

where f = focal length of lens

           v = image distance

           u = object distance

Given: Concave lens

focal length = f = -20cm

object placed in front of lens at a distance of 30cm u = -30cm

To find: The distance of image from the lens (v)

Step by step explanation:

We have lens formula

1/f = 1/v -1/u

Inserting values in the above equation

1/(-20) = 1/v - 1/(-30)

-1/20 = 1/v + 1/30

1/v = -1/20 -1/30

1/v = (-3-2)/60

1/v = -5/60

v = -12cm

Answer: The image of the object is formed at a distance of 12 cm in front of the lens.

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