The diagram shows a museum conservator aligning a plane mirror inside a display box. A low-power laser produces a light ray that reaches the mirror at an an...
Question 1 Report
The diagram shows a museum conservator aligning a plane mirror inside a display box. A low-power laser produces a light ray that reaches the mirror at an angle of 37° to the normal. The reflected ray is directed towards a light sensor. The incident ray, normal and reflected ray are in the same horizontal plane.
(a) State the law of reflection that applies at the mirror. [1]
(b) State the angle of reflection for the ray in Fig. 1. [1]
(c) Describe how the conservator could use a ruler and protractor to check the law of reflection for several different incident rays. [3]
(d) Calculate the angle through which the light ray has turned between its original direction and its direction after reflection. [2]
Answer Details
(a) The law of reflection states that the angle of incidence equals the angle of reflection. Both angles are measured from the normal. [1]
(b) The incident angle is \(37^\circ\), so the angle of reflection is \(37^\circ\). [1]
(c)
- Use a ruler to draw a normal at the point where the ray meets the mirror.
- Use a protractor to measure the angle between the incident ray and the normal.
- Measure the angle between the reflected ray and the normal and compare the two angles.
- Repeat for different incident angles, or repeat measurements and calculate a mean.
Any three of these valid steps earn credit. [3]
(d) The ray changes direction by:
\[180-(2\times37)=106^\circ\]
The turn is \(106^\circ\). [2]
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