Calculating Time Constant and Voltage Decay in a Parallel Circuit

[Solidsam]

Two 500μF capacitor are connected in parallel, and then to a 100kW (105W) resistor.
The capacitors are momentarily charged using a 1000V D.C. supply.
Find:

a) The time constant of the circuit.

b) The time “t” taken for the capacitor voltage to decay to 630 volts

c) The current in the resistor at t = 0 and t = 5 seconds


a)Is the time constant =RC=100s?

b)Do i use V=Vmax(e^(-t/RC))=99.43s?

c) do i use V=Vmax(e^(-t/RC)) again so for 0s its 0.01Amps and for 5s 0.095Amps?

 

[jambaugh]

The circuit will decay exponentially. The time constant is the (negative) reciprocal of the decay constant:

exp(kt) = exp(-t/tau).

Let's see two 500muF caps in parallel equals a single 1000muF = 1mF cap. I take it you mean a 100kOhm resistor. dQ/dt = I = - V/R = - Q/CR. So k=-1/RC, tau = RC = 100 Ohm Farads. A Farad has units of seconds per Ohm so (a.) is correct!

Yes for (b.) and for (c.) yes you find the voltage and I = V/R (in magnitude). Looks like you got it.