If two sine waves of the same frequency have a phase difference of JT radians, then

Here is a diagram of two sine waves with a phase difference of $\pi$ radians:

[asy]
unitsize(1 cm);

draw((0,-1.2)–(0,1.2));
draw((0,0)–(4*pi,0));

real g(real t) {
return sin(t);
}

real h(real t) {
return -sin(t + pi);
}

draw(graph(g,0,4pi),red);
draw(graph(h,0,4pi),blue);

label(“$y = g(t)$”, (2pi,1), E);
label(“$y = h(t)$”, (2pi,-1), E);
[/asy]

As you can see, the two waves are out of phase by one-half cycle. When one wave reaches its maximum value, the other wave reaches its minimum value.