Quick Question

Thread Starter

fishguts

Joined Sep 3, 2007
22
I am trying to find the time constant for a circuit.I want to make sure I am doing this right. My resistor is 10K while my capacitor is 5pf. this would give me:

T=RC
T=10X10^3X5X10^-12
T=10,000X.000000000005
T=.00000005s

then .00000005s would convert to .05ns right?
 

niftydog

Joined Jun 13, 2007
95
You were right until the last step.
0.00000005s = 50ns

I prefer to stay away from all those zeros and use the sum of the exponents. In this case you just do this;

10 x 5 = 50

Now add the exponents;
3 + -12 = -9

^-9 = nano so it's 50ns
 

Thread Starter

fishguts

Joined Sep 3, 2007
22
I have oe more question. I am trying to figure out the capacitor coltage after a certain time but I am stuck on using the formula I cant understand it at all. Does anyone know anylinks that explain how to use the formula better? I tried reading the article on this website but it was not any help.
 

Thread Starter

fishguts

Joined Sep 3, 2007
22
The part that is confusing me is the exponent part where it is t/T. I have no idea how the examples are getting the numbers they are getting in their solution at that part
 

niftydog

Joined Jun 13, 2007
95
Small t is the time in seconds at which you want to know the voltage.

Big T (actually the greek letter tau) is the RC time constant (T = R x C).
 

Thread Starter

fishguts

Joined Sep 3, 2007
22
ok I got the formula down. I have one more question

I have a problem that says to plot Vc for 0<t<4t using at least for points. what does it mean by this notation of 0<t<4t? I have never seen a problem like this before
 

niftydog

Joined Jun 13, 2007
95
t has to be defined before it can be used in this context, so unless they say "t=0.5s" or something then t is meaningless. You sure it's not "T" rather than "t"?

"0<t<4t" just means to plot the "t" axis from 0 up to "4 x t".
 

Thread Starter

fishguts

Joined Sep 3, 2007
22
t has to be defined before it can be used in this context, so unless they say "t=0.5s" or something then t is meaningless. You sure it's not "T" rather than "t"?

"0<t<4t" just means to plot the "t" axis from 0 up to "4 x t".
here is an attachment if it helps
it is number 3b.
 

Attachments

JoeJester

Joined Apr 26, 2005
4,348
In your problem, you are going from time zero ( 0 < t ) to four time constants ( 4 tau ) .

You were given that tau is 2 mS ... so they wanted the plot to 8 mS.
 
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