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: Calculating Current.

  1. Nov 11, 2015 #1
    1. The problem statement, all variables and given/known data
    2. Relevant equations
    Current = Voltage / Resistance.
    3. The attempt at a solution
    I know this requires me using the formula Current = Voltage / Resistance, but I'm confused to which measurements I use. I think possibly I take 0.9 from 5 volts then do 4.1 / 10000?
  2. jcsd
  3. Nov 11, 2015 #2
    Do you know the voltage division formula?

    If not, what is the total voltage drop? What is the total resistance? What is the current?
  4. Nov 11, 2015 #3
    No, I'm not aware of voltage division. How am I able to calculator any of those with an unknown resistor in the circuit?
  5. Nov 11, 2015 #4
    By using the variable name for the resistor.
  6. Nov 11, 2015 #5
    so resistance drop: 10k - R2?
    Total Resistance: 10k + R2?
    Current equals: 5 / 10 + R2?

    Sorry I'm not really sure.
  7. Nov 11, 2015 #6
    That's right (assuming you meant 5/(10k + R2)). One note though is that there's no meaning behind "resistance drop."

    So you've got an expression for the current. Now, if you can find another expression for current, you could possible equate those, and maybe then you could solve for R2. Can you find another expression for the current in that loop?
  8. Nov 11, 2015 #7
    Sorry I'm looking for other expressions involving current but not having much luck. I'm meant to be looking for formula for current correct?
  9. Nov 11, 2015 #8
    You know the formula for current: it's I = V/R. You have one expression for current that you found above. Now, notice that if you were to find another expression for current, you would have V'/R' = V/R for some voltage V' and resistance R' (since the current is the same throughout the loop). Now, if you want to find that resistance....
  10. Nov 11, 2015 #9
    [Mentor note: Quoted complete solution deleted]

    While I'm sure the OP appreciates your help, it is against the policies of the forum to outright post the answer.
    Last edited by a moderator: Nov 11, 2015
  11. Nov 11, 2015 #10
    In serie configuration, you know that current is same and tension is spread out accordingly to resistance of each components and vice-versa for parallel connections.

    Which gives us It = I1 = I2

    I will share with you my method to easily solve all equation problems. I simply write down all the know and unknown values of each relevant components and simply fill out the blanks. In this simple problem, you only have to go with the 3 basics, aka tension (E), current (I) and resistance (R). But you could also add impedance (Z), power (W) and if they asked you for a time, energy (J), Coulombs (Q), time in seconds (T), and if there was windings and capacitors, you'll have coil impedance (Xl) and capacitor impedance (Xc) and finally the impedance power (S).

    So here we go :

    Et = 5v
    E1 = ?
    E2 = 0,9v
    It = ?
    I1 = ?
    I2 = ?
    Rt = ?
    R1 = 10 kΩ
    R2 = ?

    Now it's up to you to fill in the blanks using the formula's learned in school.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted