In physics, what causes light?

Question

Please answer simply, I am not yet a physicist but a rising sophomore in high-school. What with the interaction of atoms and/or elementary particles causes the release of light? In hydrogen and helium fusion, something during that interaction causes light to form, then I asked myself,"Hydrogen and helium fusion doesn't occur inside of a light bulb, so what 'causes light?". I am sorry if you don't 'catch my drift' so to speak but what 'causes' light?

Answer 1

Be sure to continue to use 3 words when 1 will do...catch my drift?

You may benefit from incorporating the word "understand" into your vocabulary.

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Light is generally what is considered electromagnetic radiation. I say 'generally' because there are a number of different meanings. For instance a sharp blow to the back of the head might produce "light" - in the sense the brain is stimulated to produce a sensation indistinguishable from the external stimulus acting on the retina.

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Anyway, emr is composed of "photons", which are quanta, quantum mechanical wave/particles having several properties including energy and spin (polarization).

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Photons can be emitted by a number of sub-atomic particles, they can also be created out of vacuum.

(see Hawking Radiation). In quantum mechanics, there are a number of symmetries which means that there are a number of conservation laws. (There are also a number of "almost" symmetries, which result in "almost" conserved properties.) As long as the conservation laws are satisfied, particles may be transformed from one kind to another.

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It gets quite a bit simpler when considering atomic physics and chemistry of matter. Typically the emr emitted or absorbed by the nucleus is high energy, too high to be visible light. (Radioactivity is alpha rays (helium nuclei), beta rays (electrons) or gamma rays (emr), for instance). So, if we want to speak about VISIBLE light (roughly 380 -740 nm, although some people can see further into the UV) then we can restrict ourselves to electron emission. As far as matter is concerned, light is emitted when an electron loses energy. (Again, I am ignoring other Physics, Brehmstralung (emr due to charge interactions), and Cherenkov radiation (emr due to the deceleration of particles traveling faster than the speed of light (true, but (intentionally) a bit misleading)).

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In chemistry, we generally consider the effects of electrons which are bound to the nucleus of an atom. (This gets squishy, when we deal with metals, electricity, and where ballistic electrons or the band gap enter in). But taking the simple case. When a free electron becomes bound to an atom, it loses its ability to absorb (or emit) any frequency of light it pleases. The quanta of light that is allowed to be absorbed or emitted by the electron depends on the "potential well" it is in. Young students, such as yourself, can think of this as: the energy of the photon absorbed or emitted depends on the orbit of the electron. Rather, it depends on the difference in energy between the orbit the electron started in, and the orbit the electron ended up in. Only specific orbits are allowed. If a photon is emitted, then the electron must have dropped to a lower energy, since energy is almost conserved. As far as chemists are concerned, it IS conserved. If a photon is absorbed, the electron must have gained energy and gone into an excited state. We call what the electron is doing when it emits or absorbs energy a "transition". In chemistry, we consider various types of transitions. In science, often it is very useful to take a reductive approach to a situation. The reductive approach can be characterized as the "divide and conquer" strategy. So, while in the real world, transitions can not be separated so cleanly, we divide them into the following categories:

1. Electronic transitions - often emit and absorb visible, even UV emr. The "shell" (orbit, principle quantum number) of the electron is changed

2. Vibrational transitons - the distance between two nuclei (of chemically bonded atoms) changes - or more accurately, both the average distance, and the speed of vibrations around that average change. Energies are, typically, in the range of infrared emr.

3. Rotational transition - the spin (rotation) of one atom relative to another changes Note that this effect requires that the two atoms are chemically bonded together. Rotational transitions are in the range of far IR and microwave emr.

4. Spin - the spin of the electron flips (as compared to the spin of an atom, electrons have ONLY two possible spin states). radio waves and magnetic fields are used to observe this uncommon and very low energy effect. Nuclear spin, where the 'spin' of the nucleus of an atom is changed is similar, low energy and may be familiar to you as MRI medical imaging machines.

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To sum up, visible light is emitted when an electron contains more energy than it would have in its ground state, and emits some of it. The two main ways an electron can get "excited" into a higher electronic state is by 1) absorption of emr or 2) a (fairly violent) collision with another atom or particle

Perhaps it needs to be said: an object's color is caused by the electronic transitions it (its electrons) undergoes when interacting with emr.

Answer 2

When electrons change their momenta (speed and/or direction) there is a 1/137 chance they will emit a photon. When they do, both momentum and energy are conserved. The model for photon production is called the quantum electro-dynamic (QED) model.



When drawn out, it looks like a big Y where the electron starts at the bottom of the Y works up to the branch and zooms to the left. The right branch is the photon. [Look up QED Feynman Diagram on the web to see a proper diagram.]



The frequency, color, of the photon depends on the initial electron energy. The higher that is, the higher the sloughed off photon is likely to be.



The momenta of electrons can change for bonded electrons attached to nuclei and for free electrons, attached to nothing. For example, when an electron for an atom absorbs a photon, it is elevated to a higher energy level. When it pops back to a lower level, that's a change in momentum and that has a chance of sloughing off a photon whose energy is equal to the difference in the energy levels of the electron, thus conserving the energy.



Or when free electrons are goosed by the electro magnetic force imposed by a voltage across a wire, they are caused to march off in one direction and form a current. That motion also changes the momenta and induces some of them to create photons and...let the be light. It takes roughly 1E19 electrons/second to create 1 ampere of current. So when 1/137 of them produces photons, that's a lot of photons; so you can read your physics book by the light from your ceiling lamp.

Answer 3

Refraction is the exchange in direction of a wave by way of a transformation in its velocity. it is maximum ordinarily observed whilst a wave passes from one medium to a distinctive at any perspective different than ninety° or 0°. Refraction of light is the main ordinarily observed phenomenon, yet any type of wave can refract whilst it interacts with a medium, as an occasion whilst sound waves bypass from one medium into yet another or whilst water waves circulate into water of a distinctive intensity. Refraction is defined by ability of Snell's regulation, which states that the attitude of occurrence ?1 is regarding the attitude of refraction ?2 by ability of sin(i)/sin(r)=v1/v2=n2/n1 the place v1 and v2 are the wave velocities interior the respective media, and n1 and n2 the refractive indices. usually, the incident wave is in part refracted and in part contemplated; the information of this habit are defined by ability of the Fresnel equations.