This diagram is part of a safety test on a bicycle headlamp. The lamp has a flat reflector that redirects light from the bulb. Fig. 1 shows one ray reaching...
Question 1 Report
This diagram is part of a safety test on a bicycle headlamp. The lamp has a flat reflector that redirects light from the bulb. Fig. 1 shows one ray reaching the reflector. The dashed line is the normal, and the angle of incidence is 35°. The student needs to predict the reflected ray before making the reflector.
(a) State the law of reflection for the angles shown. [1]
(b) Calculate the angle of reflection. [1]
(c) Complete the path of the reflected ray on Fig. 1. [2]
(d) Explain why the normal is drawn before the angle of incidence is measured. [3]
Answer Details
(a) The law of reflection states that the angle of incidence equals the angle of reflection. Both angles must be measured from the normal. [1]
(b) The incident angle is \(35^\circ\), so the reflected angle is also \(35^\circ\). [1]
(c) The reflected ray leaves the point where the incident ray meets the reflector, on the opposite side of the normal. It must make an angle of \(35^\circ\) to the normal and have an arrow pointing away from the reflector. [2]
(d) The normal is drawn at right angles to the reflecting surface. [1] Angles of incidence and reflection are defined as angles between a ray and this normal. [1] Measuring from the surface would give a different angle, which is not the angle used in the law of reflection. [1]
Examination reminder: draw or identify the normal first, then measure the ray angle from it, not from the mirror surface.
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