5.2 Reflection
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Waves can have their directions changed when they meet an obstacle by reflection, refraction or diffraction.
Reflection
Sound and light waves reflect off surfaces. Light is reflected off surfaces into our eyes and this is why we are able to see objects. For our example of reflection, we will assume that light is travelling in the same direction and reflects off an even surface. This surface will be a mirror or something smooth and shiny. As the light hits the mirror it is reflected off at the same angle. This is the law of reflection. This law states that:
Sound and light waves reflect off surfaces. Light is reflected off surfaces into our eyes and this is why we are able to see objects. For our example of reflection, we will assume that light is travelling in the same direction and reflects off an even surface. This surface will be a mirror or something smooth and shiny. As the light hits the mirror it is reflected off at the same angle. This is the law of reflection. This law states that:
Angle of Incidence = Angle of Reflection
These angles are worked out relative to the normal. The normal is the direction of light that would reflect along the same line. It is a right angle to the mirror/ smooth shinny surface that we are using to reflect our light. We need to make sure that we measure both the angle of incidence and the angle of reflection with the normal and not the mirrored surface (note: although these angles will be the same, we should never do it).
A diagram showing light reflecting off a mirror.
Smooth surfaces will produce strong echoes as sound waves hit them and mirrors reflect light very well. Rough surfaces scatter light and sound in all directions.
Ray Diagram
A ray diagram shows how an image is formed on a plain mirror. The video will explain the steps on how to draw one. An example of a ray diagram is below this.
A ray diagram shows how an image is formed on a plain mirror. The video will explain the steps on how to draw one. An example of a ray diagram is below this.
A ray diagram.
The ray diagram must follow these rules:
- The image is the same size as the object. Mirrors change the direction of light and do not distort light by making an object seem bigger or smaller.
- The image must be as far behind the mirror as the object is in front. Again, a normal mirror will not distort distances.
- The image will be virtual because the object will appear to be behind the mirror.
- The image will be laterally inverted. This means that the left and right sides are swapped.