I'm new here, but I was wondering, if light is oscillating magnetic and electric fields, how come a powerful magnet can't disrupt, or bend light? Would it require an electromagnet oscillating at the same frequency of the light to be bent?
How are the gamma rays sent from the sun bent away from the earth?
[Physics] Light wave bending due to magnetic/ electric fields
electric-fieldsmagnetic fieldsvisible-light
Related Solutions
I think you have cosmic rays and electromagnetic radiation a little mixed-up.
We all know that without Earths magnetic field, electromagnetic radiation from the sun would cook us within minutes.
No - the Earth's magnetic field protects us from cosmic rays. High energy charged sub-atomic particles, mostly from the sun. The Earth's atmosphere does protect us from Ultra-Violet radiation (i.e. light) which would kill us.
Since visible light is the same thing as cosmic rays, except that its a different wavelength,
No, cosmic rays are charged sub-atomic particles (protons, electrons etc). Visible light, and UV, x-rays, gamma-rays, infrared, are all electromagnetic radiation of different wavelengths
I was wondering if it were possible to use magnetic fields (they would have to be pretty strong) to essentially "block" light the same way it blocks cosmic rays?
Not directly. But magnetic fields do affect how light passes through certain materials. You can use this effect to make very fast shutters by passing light through a crystal and changing the magnetic field.
A not-so-well-known fact is that it is possible to obtain a complete solution for the Maxwell equations provided you assume the charge and current distributions fall sufficiently fast as you go to spatial infinity. These solutions are generalizations of the Coulomb and Biot--Savart laws for time-dependent cases and are known as Jefimenko equations. They are presented in usual Electromagnetism textbooks and I quote here their expressions from Griffiths' book (tags according to 4th edition): $$\begin{align} \mathbf{E}(\mathbf{r},t) &= \frac{1}{4\pi \epsilon_0} \int \left[\frac{\rho(\mathbf{r}', t_r)}{R^2} \hat{\mathbf{R}} + \frac{\dot{\rho}(\mathbf{r}', t_r)}{c R} \hat{\mathbf{R}} - \frac{\dot{\mathbf{J}}(\mathbf{r}',t_r)}{c^2 R}\right] \mathrm{d}\tau', \tag{10.36} \\ \mathbf{B}(\mathbf{r},t) &= \frac{\mu_0}{4\pi} \int \left[\frac{\mathbf{J}(\mathbf{r}',t_r)}{R^2} + \frac{\dot{\mathbf{J}}(\mathbf{r}',t_r)}{c R}\right] \times \hat{\mathbf{R}} \,\mathrm{d}\tau', \tag{10.38} \end{align}$$ where I use SI units and I denote $\mathbf{R} = \mathbf{r} - \mathbf{r}'$ (Griffiths uses a cursive $r$), $t_r = t - \frac{R}{c}$ is the retarded time.
These equations are not particularly convenient for direct computation (the integrals might get quite cumbersome), but they make it some phenomenological considerations much clearer. For example, notice the dependence of the fields on the time derivative of the current: it confirms that a changing electric field isn't really the cause of induction of a magnetic field. In fact, the change in current that you need to change the electric field happens to be the very same you would need to induce the corresponding magnetic field. It's sort of a coincidence, so to speak, not a cause-consequence relation. Maxwell's equations can't really make this distinction, but once they are solved you can see it directly from the expressions.
Given this, let me try to address each one of your questions.
Q1
- At the level of Classical Electrodynamics, this is correct, but I should mention magnetic monopoles are an active line of research in both Particle Physics and Condensed Matter Physics.
- Sort of. We do observe this, but it is by pure coincidence. Fundamentally, electromagnetic fields are generated by charges and currents, sometimes by means of their time derivatives.
- Correct.
Q2
- In the absence of magnetic monopoles, magnetic fields are caused by electric currents, such as the one of a moving charge. The electric field caused by a current is due to the charge density, its time derivative and the time derivative of the current. The same current that generates an electric field generates a magnetic field, and they often can be mistaken as the cause of one another.
Q3
I'd rather see Maxwell's equations in a different way. As you mentioned, there exist electric charges and they are subject to forces related to electric and magnetic fields. This is my view of the Lorentz force law. Then the Maxwell equations say
- Wherever there is charge, the electric field diverges or converges, making close charges be attracted or repelled according o their signs
- Magnetic field lines always are closed. There are no sources or drains of magnetic field.
- The electric field always curls around a variation of magnetic field. From Jefimenko's equations we know this isn't a cause-consequence relation, but rather some sort of coincidence.
- The magnetic field curls around currents and changes in the electric field. While the former is a cause-consequence effect (the current generates the field that is curling around it), the latter isn't: it is a coincidence due to the changes in current that generates both the change in electric field and the magnetic field (we know this due to Jefimenko's equations).
Best Answer
The equations of classical electrodynamics obey the superposition principle - the fields produced by a combination of sources are just the sum of the fields that would be produced by the individual sources in isolation.
So if you have something that makes light, and a magnet, well, they'll both produce the fields they would have produced otherwise, and the overall fields will just be the sum of the two. The two do not talk to each other at all.
This works the exact same way as light and other light. If you shine two beams of light across each other, then each beam still comes out the other side.
What may be a source of confusion is the fact that you know magnets exert forces on each other, but that isn't because the fields interact with each other - it's because the fields interact with the sources. So it's true that, for instance, in principle a magnet wiggles a tiny bit at a really high frequency as light passes through it. But this is a different matter.