What is Light? Maxwell and the Electromagnetic Spectrum


Hey it’s professor Dave, let’s learn about light. Since we’ve been able to look up at the Sun, we’ve been aware of light. As darkness is one of very few things that we instinctually fear, we have always bestowed light with godlike properties, but for all of antiquity we had no idea what light really was. Figures like Newton and Huygens worked with light in the 17th century, but a more sophisticated description of light which we call classical electromagnetism was developed largely by James Clerk Maxwell in the 19th century. This theory depicts light as a transverse wave composed of oscillating electric and magnetic fields which are at right angles to each other, and perpendicular to the direction that the wave moves. We will learn more about these fields later. Just like the kinds of waves we have previously discussed, electromagnetic waves have amplitudes, wavelengths, and frequencies, but instead of different frequencies producing different pitches like sound waves, different frequencies of electromagnetic waves produce different kinds of light. If the light is visible, these frequencies will correspond to different colors. Frequencies greater than this will exist as UV radiation, x-rays, or gamma rays, and frequencies less than this qualify as infrared radiation, microwaves, or radio waves. All of these phenomena are collectively referred to as electromagnetic radiation, and they can be found on the electromagnetic spectrum. Here we can see all the wavelengths and frequencies ranging from radio waves to gamma rays, and we have found some technological use for all of these in modern society, even though they seem dramatically different, some requiring things like antennas or other equipment to manipulate. All of them are fundamentally the same thing as the light you can see with your eyeballs, they are just of different wavelengths. All electromagnetic radiation moves at the speed of light which is about 300 million meters per second in a vacuum, the fastest speed possible in the universe. This is fast enough to get from here to the moon in about a second, and since we know that all waves move at a speed that is equal to their wavelength times their frequency, this product will be equal to the speed of light for any type of electromagnetic radiation. How is it that electromagnetic radiation is produced? To answer this question we have to learn about electric fields which are coming up soon, for now let’s check comprehension. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always, feel free to email me:

64 thoughts on “What is Light? Maxwell and the Electromagnetic Spectrum

  1. Good stuff Dave.
    You maybe interested in checking my recent video regarding depth of field (for photography) and how crop factor misconceptions are still rife in the photographer /videographer community.

    I would be interested in feedback from a science perspective.

    (Uploaded last week, I did a follow up vid today.)

  2. What about Maxwell? That was a total click-bait name drop. I'm told that his famed equations are profound.. but I just can't find the handle. Break it down Professor Dave! Put your finger on it so I can tie it in a bow.

  3. Way to go Dave! Started watching your videos even when not studying! And damn you hit me with a quiz at the end (really good idea actually!). Will support you $ when out of grad school (lol)! Can't wait for next one!

  4. In science class I was stuck watching boring videos on these waves but you totally saved me. XD it's so much easier to learn when someone upbeat it talking rather than a monotone old guy. Thank you so much for making this!

  5. I am still a bit stuck understanding how visually white light emits these waves. Is it one wave that just changes in frequency slightly to cover the rainbow during its life till it reaches our eyes and gets turned into energy?

  6. Hi Professor Dave. I really like this video, but won't be able to share this one with kids. Maybe choose to include drawings of people WITH clothes on.

  7. I am taking a college level physics, I was told double transverse waves travel through a vacuum at 186,282 miles/s

  8. I have no words for the way u are presenting the topic for us. Pls keep making such videos with animations and images. Also try to make some videos related to the IIT-JEE prep, I would love it.

  9. Q: Lightspeed is constant in water and in glass and in vacuum, so why not also in Earth’s atmosphere?
    And: As lightspeed in Earth atmosphere is constant also when the lightsource is changing velocity,
    that should be different for observers when changing velocity?
    Or not?

  10. Sir, waves are disturbance moving in a medium,ie some energy is transferred through a medium.EM waves can travel through vacuum.Here no medium is distributed.why? please replay satisfactorily

  11. question why isn't the b field a cos wave . Because if we see the slope of E field at points near the origin we have dE/dt maximum and Maxwell equation describes when change of electric flux is maximum magnetic field induced is maximum. I cannot find this answer if u have time plZ solve this querry.

  12. Do we know absolutely that there is no more to the spectrum, or have we just not discovered any new way to record what may be beyond? Stupid question. I know but how can we test it or find a way to test it? Good use of Horus BTW.

  13. my radio waves, fun with frequency and time makes art and audio
    https://www.youtube.com/watch?v=QaOUqX4GzXA&t=1s

  14. Dave fast reply Thanh you. I sent you a response on your quantization part one video. I believe the answer is within Planck constant E=h f .the relationship of capacitance requires permittivity and permeability in free space versus analogy of parallel plate capacitor with quanta units of energy. The math gives h in terms of charge, permittivity, permeability and capacitance. If you want to see the math I can send you a e mail

  15. hey guys ♡ i made a whole video explaining the electromagnetic spectrum with ariana grande's discography 🙂

  16. I’ve come to the conclusion that light is a vehicle that information travels on to become knowledge.
    Think about it! How does a blue ray player work? The blue laser holds more data than the red laser thus making HD viewing possible. So that’s proof that light transfers information.
    So when you think about that on a much larger scale like the light in the universe, I think it’s feasible that that’s how creation gets it’s knowledge.
    We even have sayings like can you shed some light on it. Or don’t keep me in the dark.
    So with that being said. I think that knowledge is one of the key components to why the universe exists and why we are here. They say knowledge is power so whoever is the most knowledgeable is most likely the most powerful as well. And I guess that entity is God….
    And that would also explain why the universe is expanding at an accelerated rate. Because with just about every question that gets answered, there is a multitude of more questions. Just a thought!

  17. I fail to understand how low frequency beam and a hi frequency beam would "move" (move? is that accurate? Propagate maybe?) at the same speed through a vacuum. I see many holes that not apply to reality. Like linearity and time. Light can't be treated one dimensionally or linearly unless you shield and conduct it, then there's no true vacuum in reality cause the vacuum has no boundaries, so theoretical vacuums are artifacts and can't apply for what we mean as vacuum in reality. There is no constant. And time…you don't want to hear that is a terrestrial construct and can't apply objectively for universal formulae. If it's relative…then it means it can't be.

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