# Find the time constant for this RC circuit, help please

• Engineering

## The Attempt at a Solution

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gneill
Mentor
What are your thoughts on approaching this problem? Helpers will not provide any guidance unless you show us what you've tried or researched. No attempt means no effort. No effort means no help.

that's correct dear; what i only do was find the thevenin equivalent circuit of that problem but after that i did not know what to do because of the voltage source. Sorry for my bad english

phinds
Gold Member
that's correct dear; what i only do was find the thevenin equivalent circuit of that problem but after that i did not know what to do because of the voltage source. Sorry for my bad english
First, don't call people "dear". I'm sure you meant well, but I don't think gneill is your boyfriend. Second, SAYING that you have done the Thevinin equivalent is meaningless. SHOW that you have done it.

Does anyone want to help me or just want to reproach me ??

First, don't call people "dear". I'm sure you meant well, but I don't think gneill is your boyfriend. Second, SAYING that you have done the Thevinin equivalent is meaningless. SHOW that you have done it.
I said sorry for my english i hoped someone will understand

gneill
Mentor
Please show your work so far. The Thevenin equivalent of the driving network is very relevant!

NascentOxygen
Staff Emeritus
what i only do was find the thevenin equivalent circuit of that problem but after that i did not know what to do because of the voltage source.
The magnitude of the ideal voltage source is not relevant to calculations of the time constant of the passive circuit.

The time constant, also called Tau, is found in the equation:

τ = R x C, where R is resistance and C is capacitance

As mentioned above it is better to show your attempts at a solution first and then these "Smart-as-heck" people will steer you in the right direction.

Klystron and scottdave
gneill
Mentor
I said sorry for my english i hoped someone will understand
I definitely understand. I've worked in other countries with different local languages, so I can understand your position.

Even so, we need to see your attempt at solution before we can offer guidance. Fortunately, the language of mathematics is fairly universal. So if you could please provide your attempt at a Thevenin equivalent for the network that the capacitor "sees" that would be a good start to getting you to your desired solution.

scottdave
Homework Helper
In case you did not know, PhysicsForums differed from some other sites as to what constitutes help. While ono some sites, people might just give the solution to solving it, here people try to guide you to arriving at the solution. I don't think anybody meant to put you down.

If you show us what you've done, we will look at it and point out if you are on the right way, or need to do something different.

Let's say you have to find I2=A*e^(t/tau)+B where tau it is your constant.