capacitor (Urgent!)

[brad sue]

Hi,
I am working with capacitor now and I have this question. I am applying a square wave (from 0 to 5V) on a RC circuit.
At the output ( at the resistor) I get a positive and negative values? why is that ?
I am suspecting the fact that the capacitor create a phase difference of -90 degree(between voltage and current)..but I cannot figure out the correct answer.
please can someone help me?

[berkeman]

The capacitor is blocking the DC component of your 0-5V square wave. The DC offset of the driving source does not matter if you couple it to the load resistor with a capacitor. The cap is refered to as a DC blocking capacitor in this configuration.

[brad sue]

Thank you very much berkeman!