Question

a concave lines of focal lines 20 cm from an image at a

distance of 10 cm from lens what is the distance of object from the lions? also draw diagram​

Answer 1

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A concave lens of focal length 20 cm forms an image at a distance of 10 cm from the lens. What is the distance of the object from the lens? Also, draw ray diagram.

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✮ Given,

focal length, f = - 20 cm

image distance, v = - 10 cm

(We know, Image formed by concave lens is virtual)

◉ To find:

object distance, u = ❓

◉ Now,

By using lens formula,

➩ $-1/u + 1/v = 1/f$

➩ $-1/u - 1/10 = - 1/20$

➩ $-1/u = - 1/20 + 1/10$

➩ $-1/u = 1/20$

or u = - 20

◉ Therefore,

The object is placed at 20 cm from the concave lens.

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Answer 2

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Given :-

• Focal length = -20 cm

• Image distance = -10 cm

To Find :-

There distance of object from the lens.

Solution :-

We know that,

f = Focal length

u = Distance between mirror and object

m = Magnification

v = Distance between mirror and image

Using the formula,

$\underline{\boxed{\sf Mirror \ formula=\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f} }}$

Given that,

Focal length (f) = -20 cm

Image distance (v) = -10 cm

Substituting their values,

-1/u - 1/10 = -1/20

-1/u = -1/20 + 1/10

-1/u = 1/20

u = -20 cm

Therefore, the object is placed at a distance of 20 cm from the concave lens.