# RC circuit time constant help

Hello there,

I m very new to the forum n doesn't know that much manners of this forum..

I actually wanna do a question...

we did a practical in our university in which we determined the unknown resistance by using a neon flash bulb...

I have to submit a report on that..i have to focus on RC circuit as well as TIME CONSTANT... i have searched a lot but didn't find much...plz help me ..

## Answers and Replies

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chroot
Staff Emeritus
Science Advisor
Gold Member
Can you clarify your exact question for us? Are you asking "what does 'time constant' mean?"

- Warren

Sure..

yes i surely wanna ask that..if u could suggest any URL related to the topic ..i will ne highly thankful to you...I have to submit reort on that as i earlier said that... so the ans i want must not be a definition of 2 line...

any help from u will be highly appreciated...

chroot
Staff Emeritus
Science Advisor
Gold Member
Try using google, or a textbook. Without a specific question, I'm afraid we can't help.

- Warren

I'm not sure, but maybe it means that it's a constant used as a measure of time. Like for instance, my science teacher once said that lights, although we can't tell, flash about 60 times per second. If you were to judge things based on how many flashes a bulb makes, you might say you were using it as a "time constant". That's just my little interpretation.

Integral
Staff Emeritus
Science Advisor
Gold Member
Consider a simple RC circuit, the voltage drops in the circuit are iR due to the resistance, and q/C due to the Capacitance. Combined we get

iR + q/C = 0

but we have

$$i= \frac {dq} {dt}$$

which gives a differential equation

$$R \frac {dq} {dt} + \frac q C =0$$

This has solution

$$q = q_0 e^{- \frac t {RC}}$$

RC is called the Capacitive time constant.

Now can you as your question about this quantity?