In my opinion, electromagnetic radiation is one of the most interesting topics in all of physics because it is so well described but so hard to imagine. Just a few years back my physics prof still had trouble reasoning through questions posed about the different theories of light. Is light composed of particles or is it made up of rays (i.e. light has both properties which could make it act like waves and matter). Maybe I have yet to enter a level of physics high enough to understand why light can not be defined more clear but none the less I find the subject very interesting (edit: Actually matter also exhibits wave-particle duality!). The greatest part about EM radiation is that each sunny day brings with it all sorts of interesting optical visuals like diffraction or magnification.
Notice above that the electromagnetic radiation spectrum is made up of many different wavelength that you may not have ever thought of as the same phenomenon, like radio and light (who knew?). The most important idea to take from this spectrum is that the narrow band of EM radiation in the middle is what we humans are able to sense. Some reptiles and snakes are believed to be able to see into the infra red.
A useful tip I was once told is that infra means below and ultra means above. Ultra violet thus means above violet or with a higher frequency than violet. It's good to be able to quickly reference that.
When you see a pattern of repeating color bands it is important to be able to reason what is going on. I like to think of one distinct wavelength and imagine simple harmonic waves. Take red, imagine that there are hundreds of red SHM waves moving to this block above. As you increase the angle from path that the red were travelling you encounter a phenomenon silar to two wave traveling through two slits. Alternatively, If two waves, with the same wavelength and amplitude are travelling the same path at different speeds then they will repeatedly interact constructively and destructively (unless they are perfectly in or out of phase).
The reason that there are different colours on the film is because each colour represents a certain wavelength. If two places are yellow they are not necessarily the same thickness but are instead a multiple of that specific colour's wavelength (or depending on the materials involved, a specific ratio eg. 1/4 or 1/2 of the wavelength)
Light exhibits diffraction, that is characteristics of how waves interact with objects obstructing their path. At a macroscopic level, this is not an easily observed phenomenon. For instance, when you have sunlight going through a window, it does not appear that any diffraction occurs (i.e. you do not see variations in the intensity or light and dark banding on the floor or table etc.). However, when the slit is sufficiently small, such banding and/or variation will occur.
Single Slit coming soon
Double Slit coming soon
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