Experiment: Light Angles


The intent of this experiment is to study the rules about the angles light makes when it reflects from a mirror.

Research. Hypothesis

Light is of dual nature. Isaac Newton suggested in the 17th century that light consists of small particles that are radiated from the source. However, at approximately the same time, Christian Huygens denied that assumption and insisted that light is a wave. Only the wave theory could explain the reflection of light. At last, Maxwell in the 19th century proposed the wave particle duality. It means that in some experiments light behaves like a wave and in others its properties resemble those of corpuscles. Reflection experiments are an example of the wave nature of light. If we assume that light may behave as a wave, a light beam would not stop at the mirror surface. It would rather display certain behaviors. For example, if the surface does not absorb wave energy but reflects it totally, the wave will always reflect in such a way that the angle of incidence is exactly the angle of reflection. Based upon my research, the assumption can be made that the reflection angle will correspond to the angle of incidence as 1:1. In other words, the light reflects from the surface at the same angle at which it falls onto the mirror. The research studies the wave behavior of the light.

Materials: 1) a mirror; 2) a pencil-thin light beam; 3) a sheet of paper on which the light beam trajectory will be depicted; 4) a pencil to draw the light beam trajectory; 5) a goniometer.

Methods. Experiments: 1) streaming the light beam to the mirror at different angles. Every time the angle of incidence is changed, the corresponding angle of reflection is noted. 2) Throwing a ball at a hard surface and watching the angles of reflection.

Data & Observations

1. The light beam reflects from the surface in the plane in which it falls on it. Thus, when the angle of incidence is growing, the angle of reflection gets bigger, too. The opposite is also true: when the angle of incidence is smaller, the angle of reflection becomes less significant.

2-5. The angle of incidence is exactly the same as the angle of reflection.

6. The waves in a ripple tank behave similarly to light.

7. The ball reflects from the hard surface in a similar way to light. In this experiment we have shown that light behaves like a wave. However, we did not prove that this is the only light pattern, since other experiments need to be conducted to state such a general opinion.

Table 1. Experimental Results. The corresponding angles of incidence and angles of reflection.

Angle of Incidence

Angle of Reflection

0 º

0 º

35 º

35 º

60 º

60 º

89 º


Graph 1. The corresponding angle of incidence and angle of reflection. 1 – the angle of incidence, 2 - the angle of reflection, p – perpendicular (imaginary line), mirror surface – the surface of the mirror.


Graph 2. The linear dependence of the reflection angle of the angle of incidence is shown.


The experiment supports the stated hypothesis that light may behave as a wave. As soon as waves reflect according to the law of reflection and the reflection law is observed for light, we conclude that light behaves like a wave.

Reflections and Applications

This experiment worked well because the light source was a laser. It means that the source produced waves at a very similar destination with similar energy. I suppose that no detectible amount of energy was lost and because the mirror was clean and assuming of perfectly reflective qualities, I obtained satisfactory visualization of reflected beams. To help in saving energy, the experiment was performed in a dark room, suggesting that no other light beams (such as day light) could interfere.

It is known that sound is a wave in its nature, too. Thus, I suggest that the echo in the rocks has a similar origin as the reflective angles in the light experiment. The principles of reflection are the same, explaining the echo patterns in the mountains.

In indicator panels of some devices the reflective laws are applied. For example, in measuring devices there is a band of clean mirror inserted below the pointer as shown in the picture:

The evaluation is thus becoming much more accurate. As we know, the angle of incidence corresponds to the reflection angle. Thus, when the observer looks at the arrow in a perpendicular fashion, the angle of incidence is zero. The reflection angle is the same, and the arrow and its image in the mirror match. This means that the measurement is adequate.

The water surface may act as a mirror for light, too. If one pours water into a glass and raises it to a level above, the surface of the water, when viewed from the bottom, seems silvered due to total reflection of light.

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