Light and Electromagnetic Wave Question

[Bleepbloopblop]

Hello all,

First off, happy holidays!

I'm having some trouble visualizing what electromagnetic radiation is. If all electrons are constantly vibrating around the nucleus and have rotational acceleration, is it correct to say that electrons are constantly producing changing electric and magnetic fields? Is this not the definition of electromagnetic radiation? However, light is only emitted when electrons fall from an excited energy state to a ground state. What is the difference between this emitted light and electromagnetic radiation produced from electrons simply vibrating about? Is light electromagnetic wave that has detached from the source?

Thank you for any help.

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[Lawpy]

There are two concepts to keep in mind regarding electromagnetic (EM) radiation:

1. EM radiation requires changing electric and magnetic fields
2. Electric and magnetic fields are related to the speed of light (c = E/B)

From HyperPhysics

You are correct that electrons vibrating about the nucleus have rotational acceleration, but that is because the velocity is constantly changing. If you take a simplified look at the atom by using the Bohr model, you will see that an electron simply orbits around the nucleus similar to a planet orbiting around a star. The speed is the same, but the velocity changes because of changing direction, so there is an acceleration.

But this acceleration doesn't contribute to changing E and B fields because the acceleration is constant. Why? The electrostatic force (i.e. F = kq1q2/r^2) is constant because the electrons are orbiting from the same distance to the nucleus (same energy orbital). This means that the electric field is constant (because F = qE). By using the relation c = E/B, c is constant, E is constant, so B is also constant. We have constant electromagnetic fields, so the electrons simply orbiting around the nucleus don't emit electromagnetic radiation.

Now changing orbitals presents a different story. When an electron goes from one energy orbital to the next (higher to lower, lower to higher etc.), the distance from the nucleus changes. This corresponds to a changing electrostatic force, and thus changing electric and magnetic fields. Anytime when the electric and magnetic fields change, electromagnetic radiation is produced or absorbed.

The lower and higher energy orbitals refer to changes in electric potential energy. This means that energy is always conserved. When the electron moves farther away from the nucleus and into the higher energy orbital, some energy is required for the transition to happen. That energy is obtained from absorbing a photon (i.e. electromagnetic radiation that acts like a particle). When the electron falls to a lower energy orbital, the energy releases a photon.

Or simply:

Energy of electron in lower orbital + energy of photon absorbed = energy of electron in higher orbital (absorption)

Energy of electron in lower orbital = energy of electron in higher orbital - energy of photon absorbed -->
Energy of electron in lower orbital = energy of electron in higher orbital + energy of photon emitted (emission)

So always keep in mind that electromagnetic radiation requires changing electric and magnetic fields over some distance.

 

[Bleepbloopblop]

There are two concepts to keep in mind regarding electromagnetic (EM) radiation:

1. EM radiation requires changing electric and magnetic fields
2. Electric and magnetic fields are related to the speed of light (c = E/B)

From HyperPhysics

You are correct that electrons vibrating about the nucleus have rotational acceleration, but that is because the velocity is constantly changing. If you take a simplified look at the atom by using the Bohr model, you will see that an electron simply orbits around the nucleus similar to a planet orbiting around a star. The speed is the same, but the velocity changes because of changing direction, so there is an acceleration.

But this acceleration doesn't contribute to changing E and B fields because the acceleration is constant. Why? The electrostatic force (i.e. F = kq1q2/r^2) is constant because the electrons are orbiting from the same distance to the nucleus (same energy orbital). This means that the electric field is constant (because F = qE). By using the relation c = E/B, c is constant, E is constant, so B is also constant. We have constant electromagnetic fields, so the electrons simply orbiting around the nucleus don't emit electromagnetic radiation.

Now changing orbitals presents a different story. When an electron goes from one energy orbital to the next (higher to lower, lower to higher etc.), the distance from the nucleus changes. This corresponds to a changing electrostatic force, and thus changing electric and magnetic fields. Anytime when the electric and magnetic fields change, electromagnetic radiation is produced or absorbed.

The lower and higher energy orbitals refer to changes in electric potential energy. This means that energy is always conserved. When the electron moves farther away from the nucleus and into the higher energy orbital, some energy is required for the transition to happen. That energy is obtained from absorbing a photon (i.e. electromagnetic radiation that acts like a particle). When the electron falls to a lower energy orbital, the energy releases a photon.

Or simply:

Energy of electron in lower orbital + energy of photon absorbed = energy of electron in higher orbital (absorption)

Energy of electron in lower orbital = energy of electron in higher orbital - energy of photon absorbed -->
Energy of electron in lower orbital = energy of electron in higher orbital + energy of photon emitted (emission)

So always keep in mind that electromagnetic radiation requires changing electric and magnetic fields over some distance.

Thank you so much, that was so helpful