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Ch 33: Electromagnetic WavesWorksheetSee all chapters
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Ch 01: Intro to Physics; Units
Ch 02: 1D Motion / Kinematics
Ch 03: Vectors
Ch 04: 2D Kinematics
Ch 05: Projectile Motion
Ch 05: Using Newton's Laws
Ch 06: Intro to Forces (Dynamics)
Ch 07: Friction, Inclines, Systems
Ch 08: Centripetal Forces & Gravitation
Ch 09: Work & Energy
Ch 10: Conservation of Energy
Ch 11: Momentum & Impulse
Ch 12: Rotational Kinematics
Ch 13: Rotational Inertia & Energy
Ch 14: Torque & Rotational Dynamics
Ch 15: Rotational Equilibrium
Ch 16: Angular Momentum
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Ch 19: Waves & Sound
Ch 20: Fluid Mechanics
Ch 21: Heat and Temperature
Ch 22: Kinetic Theory of Ideal Gases
Ch 23: The First Law of Thermodynamics
Ch 24: The Second Law of Thermodynamics
Ch 25: Electric Force & Field; Gauss' Law
Ch 26: Electric Potential
Ch 27: Capacitors & Dielectrics
Ch 28: Resistors & DC Circuits
Ch 29: Magnetic Fields and Forces
Ch 30: Sources of Magnetic Field
Ch 31: Induction and Inductance
Ch 32: Alternating Current
Ch 33: Electromagnetic Waves
Ch 34: Geometric Optics
Ch 35: Wave Optics
Ch 37: Special Relativity
Ch 38: Particle-Wave Duality
Ch 39: Atomic Structure
Ch 40: Nuclear Physics
Ch 41: Quantum Mechanics

Concept #1: The Electromagnetic Spectrum


Hey guys in this video we're going to talk about something called the electromagnetic spectrum, let's get to it. Now light of different energy acts dramatically different higher energy light acts totally different than low energy light and there are particular what we would call regions of energy where light acts pretty much the same so we arranged something called the electromagnetic spectrum. Which is just an arrangement of light based on its energy into groupings of equal or sorry groupings of similar energy that shares similar properties the energy of light is proportional to the frequency of the light and so it's inversely proportional to the wavelength of the light. In this diagram right here If I step to the side you can see frequency here frequency is increasing to the left so energy is increasing to the left wavelength is doing the opposite wavelength up at the top is increasing to the right and you can actually see that light over here is very short wavelength and light over here Is very long wavelength so this graph is set up for you to read it as energy and frequency increasing to the left wavelength increasing to the right and the most important thing to keep track of is the energy that the light contains. So there are several different spectra within this several different regions several different regimes whatever the word might be we have radio waves we have microwaves we have infrared, visible and ultraviolet which are very very very tightly packed then we have an X ray and we have gamma ray. Let's look at the properties of those different types of light, now radio waves are the longest wavelength in lowest energy electromagnetic waves their used to transmit information over long distances that's why your radio is called a radio because it receives and transmits radio waves microwaves happen to have just the right amount of energy to vibrate water molecules in food which is why microwave ovens are very good at heating up things and they heat things up pretty quickly because the rate at which the energy is absorbed by the food is much faster than that in a traditional oven but all a microwave oven is doing is its blasting the food with microwave radiation which is pretty low energy light and that's causing the water to vibrate inside of the food which for friction and through other things is releasing heat and it heats up the food. Now visible light which I've paired really with infrared and ultraviolet is the portion of the spectrum that you can see you technically can't see infrared light and you technically cannot see untraviolet light but they are very very very closely sandwiched on either end of the visible light spectrum if you look above me back at the figure in the visible light they've actually coloured it in.

The acronym that typically referred sorry the acronym that typically used for the visible light spectrum to remember how the colours are arranged in terms of lowest energy to highest energy so remember on this graph on this figure that's to the left low energy to high energy is typically referred to as ROYGBIV you read it like ROY, G, BIV and it stands for red orange yellow green blue indigo and Violet. Some textbooks have dropped the indigo some professors might drop the indigo but indigo does go right there in between blue and violet it doesn't really matter either way the most important thing to remember is that red is the lowest energy light red and infrared is the lowest energy and blue or violet technically and ultraviolet is the highest energy. White light is not a true colour it doesn't belong in the visible spectrum what white light is is it's a combination of multiple colours that for some reason trip our photo cells in our eyes into appearing white it doesn't have to be all the colours fluorescent light bulbs for instance use four or five different colours. But it has to be a combination of multiple colours across the spectrum to create white light, next are X rays which are the lowest energy type of ionizing radiation. Ionizing radiation is the kind of radiation that does real damage to living organisms and all that means by ionising is if you have a little atom so we have a nucleus with a proton we have an electron all happy in its shell this ionising radiation comes in so this X ray and it kicks the electron out it ionises that atom so it removes an electron having all of those electrons hanging around outside of atoms is extremely damaging to living organisms it damages D.N.A. bonds when those D.N.A. bonds that are damaged are then repaired oftentimes mistakes are made during those reparations during their repairment sorry and those mistakes lead to things like cancer. Low energy X rays are very useful however in medical imaging as long as you don't get hit by them over and over and over and over they're most commonly used in X ray machines as the name applies and C.T. or CAT scans which stands for computed tomography top or computer animated tomography those scans are basically like rotating X ray machines that take a few hundred to a thousand X rays of you from different angles and can form using a computer a three dimensional model of what's going on inside of you one other medical instrument that I didn't mention that uses X rays is something called a fluoroscope which is like a video X ray so it takes X rays 20 times a second 10 times a second or something so you can see a moving image like a video of what's going on through you. So those are instances where X rays are very useful. But those are once again low energy X rays because high energy X rays are very very very damaging. Alright and the last bit I couldn't quite fit in that frame was gamma rays, gamma rays are the highest energy form of electromagnetic radiation they are another type of ionizing radiation and they are extremely hazardous to living organisms there are very very few practical uses for gamma rays in medicine for instance there's a type of cancer therapy called gamma knife therapy that uses very targeted gamma rays to kill tumour cells but the besides that they're typically found or sorry they are typically shielded from ever reaching humans by massive layers of led you do not want gamma rays to touch you gamma rays are the cause of most the damage from nuclear weapons or nuclear plant meltdowns. Both nuclear weapons and nuclear plants involve splitting atoms and the amount of energy that's released when atoms are split is so high that it produces gamma rays and those gamma rays go off in all sorts of different directions and they're very very damaging very very bad for you and there's all sorts of other side effects that I'm not going to get into from something like a nuclear plant meltdown like chernobyl. Let's do a quick example and then get out of here which is more energetic long wave radio waves or short wave radio waves remember energy is proportional to frequency so it's inversely proportional to wavelength so the longer the wavelength the less energy it has the shorter the wavelength the more energy it has so which is more energetic. Short wave radio waves those are definitely more energetic because energy is proportional to 1 over the wavelength it's inversely proportional to the wavelength. Alright guys so that wraps up our discussion on the electromagnetic spectrum. Thanks for watching.