1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Finding the intergral function (dQ/dt) = kQ

  1. Apr 27, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the integral (I think I'm finding the integral) of:
    [itex]\frac{dQ}{dt}[/itex] =kQ

    2. Relevant equations

    3. The attempt at a solution
    I just got feedback from my teacher, and he told me I make a mistake somewhere in this question. But I don't know where I've gone wrong?

    Where ec is a constant, so let ec=A

    ∴ Q=Aekt

    Can anyone see where I've gone wrong?
    Last edited: Apr 27, 2012
  2. jcsd
  3. Apr 27, 2012 #2
    If you substitute your solution back into the differential equation, the LHS equals the RHS, so the solution is fine. However, you wrote in an intermediate calculation that Q = ekt + ec. It can't be an addition. Try and think why it can't be an addition.

    Hint: What are rules for algebraic operations with indices?

    You made the same mistake in your next post.
  4. Apr 27, 2012 #3
    oh... Kt + c will have to go to

    ektx ec

  5. Apr 27, 2012 #4
    Yup, I can't see any other mistakes. This answer should score full marks now.
  6. Apr 27, 2012 #5

    Thanks man, I owe you one
  7. Apr 27, 2012 #6


    User Avatar
    Science Advisor

    Technically, there is one other error. The integral, [itex]\int (1/Q)dQ= ln|Q|[/itex], not ln(Q).
  8. Apr 28, 2012 #7
    ahhh... ok, thanks for that
  9. Apr 28, 2012 #8


    Staff: Mentor

    Minor point: there is no such word as "intergral" in the English language. Seeing as you have started two threads with this in the title, I thought I should point it out.
  10. Apr 28, 2012 #9
    Sorry, I have terrible spelling :frown:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook