Electricity and Magnetism: Traveling Waves and Standing Waves
Traveling Waves and Standing Waves   So today, I will start with
a general discussion on waves, as an introduction to
electromagnetic waves, which we will discuss next week.  We'll
start with a very down-to-earth equation, Y equals one-third X.
And I'm going to plot that for you, so here is Y and here is X,
and that's a straight line through the origin, Y equals one-
third X.  Suppose, now, I want this line to move.  I want this
line to move with a speed of 6 meters per second in the plus X
direction.  All I will have to do now is to replace X in that
equation by X - 6T.  Notice the minus sign.  I will go, then, in
the plus X direction.  The equation then becomes Y equals one-
third times X - 6T.  So look at it at T equals 1.  At T equals
0, you already have the line.  At T equals 1, you now have Y
equals 1/3 X - 2.  That means, here it will intersect at - 2,
and there it will intersect at + 6, and the line parallel to the
first one, this line is n