Question

Two mirror at an angle 0⁰ produce 5 images of a point. The number of images of images produced when is decreased to $\theta ^ { 0 } - 30 ^ { \circ }$ is :

• A. 9
• B. 10
• C. 11
• D. 12

Answer 1

Answer: (C)

11

Answer 2

: Number of images $= \frac { 360 ^ { \circ } } { \theta } - 1$

Where $\theta$ is in degrees

$\therefore 5 = \frac { 360 ^ { \circ } } { \theta } - 1$ or $\theta = \frac { 360 ^ { \circ } } { 6 } = 60 ^ { \circ }$

New angle, $\theta ^ { \prime } = \theta - 30 ^ { \circ } = 60 ^ { \circ } - 30 ^ { \circ } = 30 ^ { \circ }$

Number of images,$= \frac { 360 ^ { \circ } } { 30 ^ { \circ } } - 1 = 11$