CBSE Class 10 Science 2020 · Paper 31(B) · Question 22(b)

Light - Reflection and Refraction 3 marks Medium

An object is kept at a distance of 18 cm in front of a convex lens of focal length 12 cm. Use lens formula to determine the image distance and magnification of the image produced.

Answer

The image is 36 cm from the lens, on the other side, with $m = - 2$ : real, inverted and twice the size.

Using

\frac{1}{v} - \frac{1}{u} = \frac{1}{f}

with

u = - 18

cm and

f = + 12

cm:

\frac{1}{v} = \frac{1}{12} - \frac{1}{18} = \frac{1}{36}

, so

v = + 36

cm. The image is formed

36

cm from the lens, on the other side. Magnification:

m = \frac{v}{u} = \frac{36}{- 18} = - 2

, so the image is real, inverted and twice the size of the object.

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CBSE Class 10 Science 2020 · Paper 31(B) · Question 22(b)

Answer

From the board paper

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