Chapter 9

NCERT
Class 10
Science
Solutions
11. An object is placed at a distance of 15 cm from a convex lens of focal length 10 cm. Write the nature and magnification of the image.

Question:

An object is placed at a distance of 15 cm from a convex lens of focal length 10 cm. Write the nature and magnification of the image.

[Ans. The image will be real and inverted. m = 2]

Answer:

μ = –15 cm; f = +10 cm ; v = ?

Using lens formula

1/f = 1/v - 1/u

1/v = 1/f + 1/u

1/v = 1/10 + (1/(-15))

1/v = 5/150

v = +30 cm

Magnification

m = v / μ

m = + (30/(-15))

m = -2

The image formed will be real and inverted and twice the size of the object.

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