Diffraction

Diffraction in the process of waves spreding out after having passed a barrier. The extent to which waves diffract relies upon the width of the gap in comparison to the wavelength of the wave. Diffraction is a useful property to understand when studying the comparative properties of short-wave and long-wave radio communication.
Physics - Waves - Reflection, Refraction and Diffraction


This article is part 4 of the series 'Reflection, Refraction and Diffraction'. Prior knowledge may be required. If you have difficulty with this article, read its precursor here: http://exploringgcses.blogspot.com/2012/01/total-internal-reflection.html

In order to understand this fully, consider a wave that starts from one central point and radiates out. It will radiate in all directions. The waves in this article should be considered as many of these placed directly next to each other, moving forwards. Each one will radiate to the right and left, but this will be counteracted by the opposite movement of the areas right next to them, so the wave moves in a straight line forward.

When the wave passes the barrier, the very edge of it has no wave to the side of it. This means that nothing is preventing it from radiating to the side as well as forwards. This leads to the wave's edges spreading out in a circular way from the edge of the wave's main body. This diagram should illustrate the principle:

It is not neccessary for there to be two barriers and a gap: diffraction would also happen if a wave were to pass and be partially cut off by one barrier.


When the width of the aperture is equal to the wavelength, there are no pieces of the wave 'sandwiched', so all of the waves have been diffracted and there are no straight parts. Diffraction is a property shown by all waves.


This is the last of 4 articles in the series 'Reflection, Refraction and Diffraction' under the topic 'Waves' in Physics

Reflection of Waves

Physics - Waves - Reflection
When a wave strikes a barrier, it is reflected. For simplicity, we will consider a wave striking a flat barrier. The wave will strike the barrier at a certain angle, and will be reflected at the same angle.

This article is part 1 of the series 'Reflection, Refraction and Diffraction'. Prior knowledge is not required. The link to part 2 of this series is at the foot of this article.

• Whenever we measure a wave being reflected off a barrier, we use an imaginary line Perpendicular (at 90 degrees) to the barrier to measure the angles from. This line is called the Normal. 
• The angle of incidence is the angle from the normal that the wave is incident at. It is abbreviated to i
• Using the rule 'the angle of incidence is always equal to the angle of reflection', we can see that the angle of reflection will be the same. The angle of reflection is abbreviated to r.

We measure from the normal rather than the surface to avoid complications. For example, imagine that a wave was being reflected at the very edge of a mirror - you would have no surface to measure from on one side! Also, as we will go on to explore now, the surface may be uneven.

The angle of reflection is still equal to the angle of incidence. Here is what is happening: each wave strikes a particular point on the surface which will have a particular gradient. We can find this gradient by drawing a tangent to the curve (the red line on the diagram above). This is the gradient at the one point on the surface that the wave hits. Now we can apply the same technique as above to find the angle of reflection. This is what is happening on any non-reflective surface, each wave is reflected off at a different angle to the ones nearby because the surface is so uneven - the waves dont just reflect off in random directions.

Next post in series: Refraction of Light
http://exploringgcses.blogspot.com/2012/01/refraction-of-light.html