Question

Five images are produced by two mirrors kept at an angle $\theta$ in degree. Calculate the number of images produced when $\theta$ is decreased to ${\left(\theta -30\right)}^0$ .

• A. $9$
• B. $10$
• C. $11$
• D. $12$

Answer 1

Answer: (C)

Number of images $=\frac{360^o}{\theta }-1$ , where $\theta$ is in degrees
$\therefore 5=\frac{360^o}{\theta }-1$ or $\theta =\frac{360^o}{5}=60^o$
New angle, ${\theta }^{{}^{\prime }}=\theta -30^o=60^o-30^o=30^o$
Number of images $=\frac{360^o}{{\theta }^{\prime }}-1=11$