text: # Emf and Terminal Voltage
  
  nautica
  Okay here is the question:
  
  a) what is the internal resistance of a voltage source if its terminal voltage drops by 2 V when the current supplied increases by 5 A.
  
  b) Can the emf of the voltage source be found with the information supplied?
  
  I know that E = V - Ir, and I am pretty sure that a simple algebraic equation can be put together. So what formulat am I missing??
  
  Thanks
  Nautica
  
  Related Introductory Physics Homework Help News on Phys.org
  HallsofIvy
  Homework Helper
  You know that E = V - Ir so &Delta;E= &Delta;V- &Delta;I r. You are told that &Delta;E= 2volts when &Dekta;I= -5 amps. Of course, &Delta;V= 0 since the voltage source is fixed.
  Thatis: 2= -5r. Can you solve for r now? .
  
  The answer to b is NO. In effect V is the "constant of integration" when you "integrate" dE= -rdI. There is no way to find that from the information given.
  
  Last edited by a moderator:
  nautica
  I am in College Physics, we can not use calculus for an answer. So is there a reason algebraically.
  
  thanks
  nautica
  
  If u know the potential diff b/w two terminals, then u can find the emf.
  
  With this information u cannot find
  
  nautica
  So ther is no way to find emf without Potential difference???
  
  thanks
  nautica
  
  nautica
  Okay For a) here is what I got
  
  V=E-Ir
  
  or dV=dE - dIr
  
  2V = -5r
  
  so r = -.4Ohms
  
  BUT, my instructor said this was wrong b/c there I did not no the Rload and there are too many unknowns for this to be solved.
  
  I can see how part B could not be solved but this looked so simple for part a)
  
  He said this was the other equation I should have considered, but I do not see why it was needed.
  
  I = E / (Rload + r)
  
  Thanks
  nautica