# How Light Waves Propagate

1. Apr 21, 2015

### chris2112

I was hoping someone could explain something I'm not quite understanding about light waves. I've researched many sources but I'm still not understanding exactly how they propagate.

I understand that the electric field in any perpendicular section of the light ray creates a magnetic field perpendicular to it or vice versa, but I do not understand how they create each other in the direction of the ray to actually create it. I'm hoping someone can help me out with this. Thank you.

2. Apr 22, 2015

### Delta²

That is due to Faraday's Law and Maxwell-Ampere's Law in integral form. It follows from those two laws that the fields cannot be confined in free space (unless they interact with matter), and that when you have the fields in a finite volume of space and those fields are time varying then they create fields in every other volume that encloses that first finite volume, so essentially you just cant confined the fields unless you make em interact with matter.

3. Apr 23, 2015

### Staff: Mentor

Think about a more familiar example: a water wave. The water at any one point only goes up and down in the vertical axis, yet the wave somehow propagates horizontally along the surface. What's going on here is that as gravity pulls the high spot down, the water underneath the high spot has to get out of the way, so is forced sideways causing the water next to the high spot to have to get out of the way... And up is one of the directions that water can move. So the downwards movement of the high spot creates a new high spot adjacent to it.

As Delta2 says, the analogous behavior with electrical and magnetic fields is described by Faraday's and Maxwell's laws.