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Subjects
Science CBSE Homework Assignments
Class 10
Light reflection and refraction
Image formation by spherical mirrors

1. Image formation in mirror

Task:

5 m.

Section D: Give a long answer to the question given below.

A \(10\ cm\) long pencil is placed 5 cm in front of a concave mirror having a radius of curvature of \(40\ cm\).

Determine the position of the image formed by this mirror.

What is the size of the image?

Draw a ray diagram to show the formation of the image as mentioned in the part (i).

The focal length of the mirror is

\(-40\ cm\)
\(-20\ cm\)
\(20\ cm\)
\(40\ cm\)

The mirror formula is

\(\frac{1}{f}\ =\ \frac{1}{v}\ -\ \frac{1}{u}\)
\(\frac{1}{f}\ =\ \frac{1}{R}\ -\ \frac{1}{u}\)
\(\frac{1}{f}\ =\ \frac{1}{v}\ +\ \frac{1}{u}\)
\(\frac{1}{f}\ =\ \frac{1}{u}\ -\ \frac{1}{v}\)

The image distance is

\(-6.67\ cm\)
\(6.67\ cm\)
\(20\ cm\)
\(-20\ cm\)

The formula for magnification is

\(m\ =\ \frac{h_i}{h_o}\ =\ \frac{-v}{u}\)
\(m\ =\ \frac{h_o}{h_i}\ =\ \frac{-v}{u}\)
\(m\ =\ \frac{h_i}{h_o}\ =\ \frac{v}{u}\)
\(m\ =\ \frac{h_o}{h_i}\ =\ \frac{v}{u}\)

The height of image is

\(13.34\ cm\)
\(6.67\ cm\)
\(-6.67\ cm\)
\(-13.34\ cm\)

Important!

Draw the ray diagram in white paper and compare it with the answer.

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