# voltage drop

Discussion in 'Homework Help' started by myoplex11, Oct 3, 2007.

1. ### myoplex11 Thread Starter New Member

Oct 3, 2007
5
0
A 6V DC voltage source is connected across both a 5kohm resistor and a 10 nF capacitor in series. The voltage drop across the resistor is what?

2. ### Dave Retired Moderator

Nov 17, 2003
6,960
150
v(t) = V*exp(-t/RC)

V = voltage at source
R = resistance
C = capacitance

Dave

3. ### myoplex11 Thread Starter New Member

Oct 3, 2007
5
0
thanks but the time is not given

4. ### Dave Retired Moderator

Nov 17, 2003
6,960
150
From the above equation the voltage across the resistor is a function of time, so it is pretty essential to the question - could it be asking you for the initial or final voltage across the resistor?

Dave

5. ### myoplex11 Thread Starter New Member

Oct 3, 2007
5
0
it is the final voltage across the resistor

6. ### Dave Retired Moderator

Nov 17, 2003
6,960
150
For the final voltage, and in the absence of a specific time, in the above equation use t = $\infty$, therefore you get:

v(t) = 6*exp(-$\infty$)

exp(-$\infty$) = 0, therefore in this ideal scenario the voltage across the resistor is 0V, i.e. the entire source voltage is across the capacitor.

Dave