Question

q1

1. A point object is placed at a distance 10 cm and its real image is formed at a distance 20 cm from a concave mirror. If the object placed is moved by 0.1 cm towards the mirror, the image will shift by about.

(1) 0.4 cm away from the mirror ​(2) 0.4 cm towards the mirror
(3) 0.8 cm away from the mirror ​(4) 0.8 cm towards the mirror

Answer 1

Dear Student,
$$\begin{gathered} u=-10,v=-20cm \\ \frac{1}{v}+\frac{1}{u}=\frac{1}{f} \\ \frac{1}{-20}+\frac{1}{-10}=\frac{1}{f} \\ f=\frac{-20}{3}cm \\ \frac{dv}{v^2}+\frac{du}{u^2}=0 \\ \frac{dv}{{20}^2}+\frac{0.1}{{10}^2}=0 \\ \frac{dv}{{20}^2}=-\frac{0.1}{{10}^2} \\ dv=-0.4cm \\ sothe0.4cmawayfromthemirror. \\ Regards \end{gathered}$$