eli5 What is light made up of? Where does it come from inside a torch? Is light just un-containable luminous particles than can never be studied as a single unit inside a Microscope?
In: Physics
Hi /u/po4165!
>What is light made up of?
The term “light” is usually used to describe the visible part of the [electromagnetic spectrum](https://en.wikipedia.org/wiki/Electromagnetic_spectrum). That is, light is a wave comprising of excitations in the electric and magnetic field, with a wavelength of roughly 400-700 nanometers. [Quantum mechanics](https://en.wikipedia.org/wiki/Quantum_mechanics) tells us, that these waves do not transmit energy in a continuous stream, but instead energy is transmitted in discrete packages. These packages are called [photons](https://en.wikipedia.org/wiki/Photon).
>Where does it come from inside a torch?
I’m not sure if you are using the word torch to describe a the candle-looking thing or a flashlight, and the answer would differ slightly depending on the meaning.
Modern flashlights use [light-emitting diodes (LEDs)](https://en.wikipedia.org/wiki/Light-emitting_diode) to generate light. LEDs typically make use a process called [electroluminiscence](https://en.wikipedia.org/wiki/Electroluminescence), where photons are emitted when electrons transition to a lower energy-level (so-called “holes”). An intuitive understanding of this process can be gained, when considering conservation of energy: when an electron is excited and at some point later drops back to a lower energy-level, the energy has to go somewhere. In the case of LEDs, the energy between the excited state and the lower energy state is emitted in the form of a photon.
>Is light just un-containable luminous particles than can never be studied as a single unit inside a Microscope?
Photons are a bit special in so far as they are mass-less particles. And as it turns out, all mass-less particles must always travel at the speed of light c (through vacuum). And crucially, it doesn’t matter how fast an observer is traveling relative to the source of the light, she will always measure the photons to travel at c.
A consequence of this is that there are no valid frames of reference, relative to which photons are at rest. While photons *do* slow down when traveling through a material, they can never be studied on their own and at rest.
Light is made up of photons, which in turn are small packages of energy moving at light speed.
Light is created whenever small amounts of energy are released in subatomic processes. This usually happens when electrons around nuclei are infused with energy, then revert back to their “natural” state – they get rid of the excess energy by emitting a photon. This also happens during lightning strikes (infusing the air’s electrons with massive energy, then releasing it as light) and inside light bulbs (infusing a gas’ electrons with energy through electricity, which then releases the excess energy as photons).
You can’t study light particles in a microscope, not just because of their speed, but also because in order to see them you need them to be absorbed by your retina, i.e. destroying them. When you study a microbe in a microscope, you do that by bombarding it with photons (light), then capturing the light that gets bounced back from the microbe, concentrate a lot of that in the lenses and absorb it with your eyes’ retinas. From that absorbed light you then infer the qualities of the microbe. If you were studying photons, you would basically bombard photons with other photons, which would combine their energy and possibly emit different photons; Either way you’d actually see the result of the merger, not the original photons.
Photons. Depending how you look at them, they are either a wave across the electromagnetic spectrum, or a stream of tiny little particles being emitted from chemical reactions.
That explanation won’t get you a doctorate but should bore a 5yr old enough to satisfy them.
light is a vibration of the electromagnetic field.
It comes from the electrons within atoms and molecules, when they lose emergy they emit light.
We don’t really know what light “is”. We have just been able to observe and determine certain characteristics about how it behaves. Light has no mass, but it has momentum. It can act both as a discrete particle and as a wave. It doesn’t require a medium to travel through, which is how it travels through space. The base unit of light is called a photon. This is a single particle-like unit of light (although it simultaneously acts like a wave).
It is the same with all matter/particles. We know that protons and neutrons are made up of 3 smaller particles called quarks, but we don’t know what a quark really “is”. Its called a fundamental particle because at this point, as far as we can tell, it is the base “stuff” that makes a proton or neutron. We haven’t been able to break a quark into anything smaller. We know there is a relationship between it and energy (most famously with the equation E = MC^2). Electrons are another fundamental particle. We haven’t been able to break an electron into any smaller.
Effectively, a photon is a photon because it is made of nothing but photon, an electron is an electron because it is made of an electron, and quarks are quarks becuase they are made of a quark.
Light can be generated in many ways. One common way is when electrons drop from a higher energy to a lower energy. Energy cannot be destroyed, so it has to go somewhere. In this case it is emmited in the form of a “photon” or light. This photon will have the exact amount of energy that was lost when the electron changed energy levels.
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