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

Light - Reflection and Refraction 3 marks Medium

An object is kept at a distance of 30 cm in front of a concave mirror of focal length 20 cm. Use mirror formula to determine the position and magnification of the image produced.

Answer

The image is formed 60 cm in front of the mirror and the magnification is $- 2$ : real, inverted and twice the size.

Using

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

with

u = - 30

cm and

f = - 20

cm:

\frac{1}{v} = - \frac{1}{20} + \frac{1}{30} = - \frac{1}{60}

, so

v = - 60

cm. The image is formed

60

cm in front of the mirror. Magnification:

m = - \frac{v}{u} = - \frac{- 60}{- 30} = - 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(a)

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