Notices
Results 1 to 6 of 6

Thread: Time Constants

  1. #1 Time Constants 
    Forum Freshman
    Join Date
    Feb 2013
    Posts
    16
    My nephew (a high school student) asked me last week how time constants work. Time =resistance X capacitance. T=RC
    He was please with this simple explaination:

    T=RC T= VOLTS/AMPS x COULOMBS/VOLT

    T= JOULES PER COULOMBE/COULOMBS PER SECOND x COULOMBS/JOULES PER COULOMBS

    Reducing this shows that T=Seconds


    Reply With Quote  
     

  2.  
     

  3. #2  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,710
    Since the definitions of the units used (Joules, Coulombs) is based on seconds ((kg.m2)/sec2 and Amp.sec) it seems a long way round to "prove" a tautology.


    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  4. #3  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,795
    If you charge or discharge a capacitor through a resistor it will follow an exponential decay curve. The time constant will be the product of the resistance and the capacitance. Time constant for exponential decay is the time to reach 1-1/e of the final value.

    RC time constant - Wikipedia, the free encyclopedia
    Time constant - Wikipedia, the free encyclopedia
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    Feb 2013
    Posts
    16
    Quote Originally Posted by Dywyddyr View Post
    Since the definitions of the units used (Joules, Coulombs) is based on seconds ((kg.m2)/sec2 and Amp.sec) it seems a long way round to "prove" a tautology.
    Not a long way around to a beginner who wants to understand the equation. "T=RC. Now he knows and doesn't have to memorize.
    Reply With Quote  
     

  6. #5  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,710
    Right...
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  7. #6  
    Suspended
    Join Date
    Apr 2007
    Location
    Pennsylvania
    Posts
    8,795
    Quote Originally Posted by thinkatron View Post
    Quote Originally Posted by Dywyddyr View Post
    Since the definitions of the units used (Joules, Coulombs) is based on seconds ((kg.m2)/sec2 and Amp.sec) it seems a long way round to "prove" a tautology.
    Not a long way around to a beginner who wants to understand the equation. "T=RC. Now he knows and doesn't have to memorize.
    All he's really learned is that RC has the units of time. You could use the same process to "prove" that kinetic energy is mv^2 or 5 mv^2 or whatever.
    Reply With Quote  
     

Similar Threads

  1. A new way of thinking about G and c. Constants?
    By Juanma in forum Astronomy & Cosmology
    Replies: 11
    Last Post: August 6th, 2012, 11:10 AM
  2. Mathematical constants in other universes
    By jmd_dk in forum Physics
    Replies: 3
    Last Post: August 4th, 2009, 02:36 AM
  3. Mathematical constants
    By accountabled in forum Mathematics
    Replies: 16
    Last Post: December 21st, 2008, 12:32 PM
  4. Conformities to law are found between the constants of
    By polevikov in forum Pseudoscience
    Replies: 0
    Last Post: December 17th, 2008, 03:56 AM
  5. Mathematical constants in Nature
    By VMStudent in forum Mathematics
    Replies: 4
    Last Post: June 10th, 2008, 03:00 PM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •