Results 1 to 2 of 2

Math Help - Can anyone solve me this maths equation, please?

  1. #1
    Newbie
    Joined
    Jan 2009
    Posts
    2

    Can anyone solve me this maths equation, please?

    V = 240 ( 1 - e -(rt)L )

    given R = 1 ohm
    given L = 200mH

    calculate the time when the voltage is expected to be 140v
    been trying for ages just cant crack it
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by lewuk09 View Post
    V = 240 ( 1 - e -(rt)/L )

    given R = 1 ohm
    given L = 200mH

    calculate the time when the voltage is expected to be 140v
    been trying for ages just cant crack it
    First you should make sure you post the correct equation. I assume it's a series RL circuit so note the missing vinculum I have added (in red).

    Now substitute the given data into the equation (note that 200mH = 0.2 H):


    140 = 240 \left( 1 - e^{-t/0.2}\right) = 240 \left( 1 - e^{-5t}\right)


    \Rightarrow \frac{140}{240} = 1 - e^{-5 t}


    \Rightarrow \frac{7}{12} - 1 = - e^{-5 t}


    \Rightarrow \frac{5}{12} = e^{-5 t}


    \Rightarrow \ln \frac{5}{12} = -5 t


    and I'm sure you can do the finishing touches.

    (Since I've worked in SI units the time you get will be measured in seconds).
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: December 28th 2010, 01:22 AM
  2. maths - roots of equation
    Posted in the Math Topics Forum
    Replies: 5
    Last Post: December 8th 2009, 10:15 PM
  3. Maths help with equation of line and algebra?
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: February 1st 2009, 09:44 AM
  4. Please help me to solve these maths problems?
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 23rd 2008, 11:36 AM
  5. help me solve this considered easy maths question
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: July 12th 2008, 10:57 PM

Search Tags


/mathhelpforum @mathhelpforum