![]() The most amount of diffraction happens when the wavelength is a similar size to the gap. ![]() ![]() (a picture would help to explain this)ĭiffraction: Waves spread out as they enter an aperture (gap). As it slows down it changes direction, meaning that the angle that it is travelling at changes - the angle becomes closer to the normal. Refraction: When light travels from air into another material (such as glass) at any angle other than normal (perpendicular), it slows down. Remember that in reflection the angle of incidence (this is the angle that the initial wave makes from the normal), is the same as the angle of reflection (the angle that the reflected wave makes from the normal). Reflection: This is when a wave hits a surface (e.g light hitting a mirror) and is bounced back. Refraction is when light rays enter a different medium of different optical density and change direction or bend. In this case, the Law of Reflection is valid, ie the angle of incidence equals the angle of reflection. On the diagram it is useful to mark on a line for 'normal', this is a straight line that is perpendicular (makes a 90 degree angle) with a surface. Reflection of light occurs when light rays strike a surface and bounce back or reflect off it. It can also be helpful to draw diagrams of each to help you to remember the difference. This can be observed in a simple experiment in which a source of sound such as a transmitter sends sound at a certain angle to the normal to a wall and a higher sound is received from reflection at the same angle. angle of incident is equal to the angle of reflection. This asymmetrical slowing of the light causes it to change. Reflection, Refraction, Diffraction and Interference of Sound Waves. Wave crests getting a lot steeper as they run up on the slope.These are all properties of waves and their definitions are useful to remember for exams. When light enters a slower medium at an angle, one side of the wavefront is slowed before the other. Ripples on the surface by a gust of wind. What I wanted to show on this picture is a close-up of the turbulent wake of the ship, but it’s really difficult to see so I’ll let that pass for today.Īnd the picture below shows so much cool stuff: Waves radiating from that pylon. The wave passing an obstacle is, in a way, the same as the wave passing through two wide slits which are very close to each other, only separated by the obstacle: The edges of the wave crest at the edges of the “slits” also start radiating out as circle segments!Īnd there are, of course, ships. This is a process called diffraction: The change of direction after a wave crest has passed either through a slit and then starts radiating from that slit as circle segments, or, in this case, an obstacle. That means that if a wave crest is running on a slope with one side being in shallower water while the other one is still in deeper water, it will change direction towards the shallow water because the shallow side of the crest is slowed down while the deeper side keeps on moving faster, thus forcing the whole crest around a curve.īut in this picture series there is more to see: See how the wave crest gets deformed after it has passed that obstacle? Diffraction of waves ![]() Or, more scientifically speaking, the dispersion relation for shallow water waves is a function of water depth: The shallower the water, the slower the waves. Why do waves change direction as the water depth changes? As waves run from deep into shallow water, at some point they start to “feel” the bottom, which slows them down. But then looking at the next wave crest in-shore, it is almost parallel to the shore! Assuming that both crests come from the same wave field, so that the second one was in the same position as the other one only moments before (which I know it was because I observed it), something clearly happened between then and now. If you focus on the wave crest that is just offshore of that little obstacle in the water (curious enough, a piece of brick wall), you clearly observe that angle. Simple depictions of (a) reflection of a beam of light from a surface (b) refraction of light through a medium of higher refractive index and (c) diffraction. A little more wave watching, today with a focus on how waves change direction when they run into shallow water. Let’s look at this beautiful wave and see what happens when it reaches the shallow shore.Ībove, you see the wake of the pilot ship, consisting of many wavelets that propagate as parallel wave crests towards the shore.īelow, you see that the wave is propagating at an angle to the shore (something around 45 degrees, maybe?). ![]()
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