A simple RC circuit is shown below, where R=2.50 megaohms and C=1.50 microfarads. The capacitor has a charge of 90 microcoulombs before the switch is closed. The switch closes at 0s.
a) determine the time constant of the circuit
b) determine the charge on the capacitor 3.00 s after the switch closes
c) determine the time when the current through the resistor is 6.50 microamperes