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Calculating Current.

  • #1
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Homework Statement


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Homework Equations


Current = Voltage / Resistance.

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?
 

Answers and Replies

  • #2
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Do you know the voltage division formula?

If not, what is the total voltage drop? What is the total resistance? What is the current?
 
  • #3
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Do you know the voltage division formula?

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

Sorry I'm not really sure.
 
  • #6
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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?
 
  • #7
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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?
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?
 
  • #8
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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....
 
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  • #9
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[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:
  • #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.
 

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