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, $\theta ^{'}=\theta -30^{o}=60^{o}-30^{o}=30^{o}$
Number of images $=\frac{360^{o}}{\theta '}-1=11$