Question

An object is placed at a distance of 20 cm from
a convex lens of focal length 10cm
find the location, Nature and magnification​

Answer 1

Answer :-

Location of image : 20 cm behind lens .

Nature : Real, inverted .

Magnification : -1

Explanation :-

We have :-

→ Distance of the object (u) = 20 cm

→ Focal length (f) = 10 cm

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From sign convention, we have :-

• u = -20 cm

• f = + 10 cm

According to lens formula :-

1/v - 1/u = 1/f

⇒ 1/v = 1/f + 1/u

⇒ 1/v = 1/10 + 1/(-20)

⇒ 1/v = 1/10 + (-1)/20

⇒ 1/v = (2 - 1)/20

⇒ 1/v = 1/20

⇒ v = 20 cm

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Now, from the formula of magnification :-

m = v/u

⇒ m = 20/(-20)

⇒ m = -1

Answer 2

Given :-

An object is placed at a distance of 20 cm from  a convex lens of focal length 10cm

To Find :-

Position, Nature, Magnification

Solution :-

We know that

1/f = 1/v - 1/u

1/10 = 1/v - 1/-20

1/10 = 1/v - (-1)/20

1/10 + (-1)/20 = 1/v

2 + (-1)/20 = 1/v

2 - 1/20 = 1/v

1/20 = 1/v

1v = 20

v = 20

Now

m = v/u

m = 20/-20

m = -20/20

m = -1