About plotting two independent Y-axis on the one plot

Hello all:

One of the classic problem in RC charge and discharge circuit in the usual
freshman physics course is being able to plot the voltage rise with a
current discharge on a single plot so that their intersection in time is
determined.

Now how does one do it with a wxplot2d() with two independent Y-axis on one
and the same plot?

Well this looks easy for a simple case of just one plot:
R:10e3 $ C:10e-6 $ %tau:R*C; V[max]:10 $
v(t)=V[max]*(1-(exp(-t/(R*C))));
wxplot2d(v(t),[t,0,0.5]);

and
i(t):=(V[max]/R)*(exp(-t/(R*C)));
wxplot2d(i(t),[t,0,0.5]);

but I got into trouble with the temptation with just writing out:
wxplot2d([v(t),i(t)],[t,0,0.5]);

which only shows the voltage rise. Easily done in MS Excel but I need the
symbols for purposes of instruction.

Any tip?

Regards,
Berns B.
Dept. of Physics - University of San Carlos