# Homework Help Needed

#### ace2015

Joined Oct 24, 2017
15
A current I Amps flows through a capacitor at time t seconds is given by:

I=#(1-e^((-t)/τ))

where the time constant τ is 0.8 seconds. Determine:

(i) The current
after (12 + ∆) seconds.

(ii) The time taken for the current to reach (8 + ∆) amps

#### MrAl

Joined Jun 17, 2014
8,479
Sorry I am new to this site, this is my first post.

Do you know how I can put this in the home work section?
Hi,

Bertus moved it for you

Now, what does your number symbol mean in your post "#" is that the voltage or current or something else ?
Maybe you could rewrite that in a more clear form.

#### bertus

Joined Apr 5, 2008
21,557
Hello,

Do you mean 3 instead of the # ?
Can you show your attemp to solve the problem?

Bertus

PS I revomed some posts that are not needed anymore.

#### Alec_t

Joined Sep 17, 2013
12,212
Welcome to AAC!
Are there any constraints on Δ?

#### ace2015

Joined Oct 24, 2017
15
Thanks for moving it for me.

I am totally perplexed by this problem.

As far as I know # is an unknown number that needs to be worked out. It is written as that in my assignment question.

Bertus, you are a genius yeah it's a mistake by my college it is supposed to be 3 definitely.

I will get back to you if I need any more help I should be able to work this out now knowing that the college made a typo.

Best regards.

#### Bordodynov

Joined May 20, 2015
2,907
In the problem of uncertainty, there is a lack of numerical data (eg #)

#### WBahn

Joined Mar 31, 2012
26,398
My guess is that Δ might either be an independent variable (though it is two different parameters since one is a time and the other is a current) or it might be a student-dependent parameter so that each student is working a different problem.

#### RBR1317

Joined Nov 13, 2010
664
Do you get extra points for realizing that there is no physical circuit where the current through a capacitor begins at zero and rises to some constant value (beyond 5τ)?

#### MrAl

Joined Jun 17, 2014
8,479
Do you get extra points for realizing that there is no physical circuit where the current through a capacitor begins at zero and rises to some constant value (beyond 5τ)?
Hi,

Yes, this would normally be I*e^(-t/tau) unless they want the student to just take it verbatim.