for resistor:

for inductance:

for capacitor:

That is the reason why for AC signal ,the voltage for inductance or capacitor are 90 degree out of phase with current.

For electromagnetic wave, it is another sets of equations (it is also related to the above equations under some conditions)

and

For EM wave in free space, I=0

Combine the above two equations will give us

and

which are standard form for wave equation.

You can chek out http://en.wikipedia.org/wiki/Electromagnetic_wave for derivation

The wave can be represented with

The change on electric field (flux) will product magnetic field distribution ()at near by space.

The time derivative will produce 90 degree phase differences.

However, the curl will also produce another 90 degree phase differences.

That is why the net effect is in phase. The electric field is in the same phase with magnetic field in free space.

It is possible to produce out of phase EM wave in wave guide.

You are welcomed to check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35.0]Propagation of Electromagnetic Wave[/url]

:=)