# Current term maxwell equations

1. Jan 4, 2012

### commelion

yo

ok progress on the electromagnetic wave front is progressing nicely....finally, but

i have stumbled on a area that i need some help with. see below

when maxwell took amperes law, he added whats known locally ! as the current term, this was done because he realised that a changing magnetic field gives rise to an electric field.

Q how does this current term suggest that light must be an electromagnetic wave ?

if any one has any consise explainations i would appreciate it, i dont need the maths as i have them in front of me. just think of it as a table quiz kind of answer !!

2. Jan 4, 2012

### yungman

Light is just EM wave in much higher frequency spectrum. It is a frequency thing. I am not good enough to explain in plain English, from my understanding:

$$\nabla \times \vec H= \vec J +\epsilon_0 \frac{\partial \vec E}{\partial t}\;\Rightarrow \int_c \vec H\cdot d\vec l = I_ C+I_D\;\;\hbox { where it is conduction current and displacement current respectively.}$$

This just said a varying conduction and/or displacement current will produce a varying magnetic field. Which in turn the varying magnetic field will be accompanied with a varying electric field by:

$$\nabla \times \vec E =-\frac {\partial \vec B}{\partial t}$$

But nothing is said about the frequency. As said, light is just the upper range of the EM wave frequency.