# Calculus Spreadsheet for an RC circuit

• Nov 21st 2011, 04:43 AM
maali5
Calculus Spreadsheet for an RC circuit
Calculus
I have recently been given the following question but I have no idea how to differntiate the equation or plot the equations. Can you please help me?

Capacitor = 100 nF
Resistor = 47 kΩ
Supply voltage = 5 V
Charging characteristic for a series capacitive circuit:

v=V(1- e-^(1/T)) where T=CR

n Use a spreadsheet to plot the charging curve over the range 0 to 20 ms (milliseconds).
n Differentiate the charging equation and find the rate of change of voltage at 6 ms.
• Nov 21st 2011, 06:58 AM
skeeter
re: Calculus Spreadsheet for an RC circuit
Quote:

Originally Posted by maali5
Calculus
I have recently been given the following question but I have no idea how to differntiate the equation or plot the equations. Can you please help me?

Capacitor = 100 nF
Resistor = 47 kΩ
Supply voltage = 5 V
Charging characteristic for a series capacitive circuit:

v=V(1- e-^(t/T)) where T=CR

n Use a spreadsheet to plot the charging curve over the range 0 to 20 ms (milliseconds).
n Differentiate the charging equation and find the rate of change of voltage at 6 ms.

corrected equation ... voltage across the capacitor is a function of time.
• Nov 21st 2011, 07:12 AM
Deveno
Re: Calculus Spreadsheet for an RC circuit
hint on how to differentiate the equation: V and T are constants. we can re-write the equation as:

v = V - Ve^(-t/T).

the first term in this difference disappears in the derivative, so we only have to take the derivative of -Ve^(-t/T).

the -V in front is just a constant, so v'(t) = (-V)(d/dt)(e^(-t/T))

and e^(-t/T) is of the form e^(at), where in this particular case, a = -1/T.
• Nov 21st 2011, 12:11 PM
maali5
Re: Calculus Spreadsheet for an RC circuit
Skeeter: Thanks, I made a spelling mistake

Question: Use a spreadsheet to plot the charging curve over the range 0 to 20 ms (milliseconds)

T=CR

T=0,1 x 47000
t=0.00470

T v=V(1- e-^(t/T)) How can I draw the spreadsheet when answers =5?

0 v=5(1- e-^(0/T)) 0
1 v=5(1- e-^(1/T)) 5
2 v=5(1- e-^(2/T)) 5
3 v=5(1- e-^(3/T)) 5
4 v=5(1- e-^(4/T)) 5
5 v=5(1- e-^(5/T)) 5

6 Etc,
..
...
...
20 v=5(1- e-^(20/T)) 5

Deveno: Cheers for the hints
• Nov 21st 2011, 12:32 PM
skeeter
Re: Calculus Spreadsheet for an RC circuit
Quote:

Originally Posted by maali5
Skeeter: Thanks, I made a spelling mistake

Question: Use a spreadsheet to plot the charging curve over the range 0 to 20 ms (milliseconds)

T=CR

T=0,1 x 47000
t=0.00470

T v=V(1- e-^(t/T)) How can I draw the spreadsheet when answers =5?

0 v=5(1- e-^(0/T)) 0
1 v=5(1- e-^(1/T)) 5
2 v=5(1- e-^(2/T)) 5
3 v=5(1- e-^(3/T)) 5
4 v=5(1- e-^(4/T)) 5
5 v=5(1- e-^(5/T)) 5

6 Etc,
..
...
...
20 v=5(1- e-^(20/T)) 5

Deveno: Cheers for the hints

time is in milliseconds, not seconds ...

t should be 0, .001, .002, .003, ... , .020
• Nov 21st 2011, 12:35 PM
maali5
Re: Calculus Spreadsheet for an RC circuit
Genius! but can you explain how to calculate it.

I know 1 seconds is 1000millisecond.
• Nov 21st 2011, 12:48 PM
maali5
Re: Calculus Spreadsheet for an RC circuit
I have done the graph and have the attached to the page.

Is it correct?

Sooory to bother you with questions
• Nov 21st 2011, 12:48 PM
skeeter
Re: Calculus Spreadsheet for an RC circuit
Quote:

Originally Posted by maali5
Genius! but can you explain how to calculate it.

I know 1 seconds is 1000millisecond.

sure ...

$\displaystyle V(.001) = 5 \left(1 - e^{-\frac{.001}{.0047}} \right) = 0.95282...$

... and so on. You should do some research on how to do it in a spreadsheet ...

how to generate a graph in excel - Google Search