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Series circuit blues

  • Thread starter Dazed
  • Start date
  • #1
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Homework Statement



2. For the following circuit, find RT, IT, I3, V1, V3, V5.

http://img520.imageshack.us/my.php?image=m17aje5.gif


Homework Equations



V = IR, ohms law, Kirchoff's laws

The Attempt at a Solution



RT = R1 + R2 + R3 + R4 + R5 + R5
RT = 20 + 22 + 30 + 27 + 40 + 20
RT = 159 ohms

IT = V/RT
IT = 120 V / 159 ohms
IT = 0.75 amps


I have the total resistance and total current.. I'm not sure exactly how to go about finding the current at I3 though. Any help would be appreciated.

voltage, minus the voltage drop of the 2 resistors before it, / resistance of the 2 resistors before it? I'm not sure.
 

Answers and Replies

  • #2
19
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In a series circuit, the current is constant all the way round, so the current at I3 is the same as the IT that you calculated.

As the current is the same through all the resistors, you can calculate the voltage drop across each resistor using V=IR

Hope that helps
 
  • #3
26
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That does help a lot, thanks.

But it raises one question for me, you say the current is the same through all resistors, but as I understand, the resistance causes the current to drop.

Hence the I = V / R formula

The previous question I did was "What is the current through each resistor?" in "A circuit with a 6.0 V battery has a 3 ohm resistor and a 15 ohm resistor in series."


At a 3 ohm resistor

I = V / R
I = 6 v / 3 ohm
I = 2 amps

At a 15 ohm resistor

I = V / R
I = 5 v / 15 ohm
I = 0.33 (repeating)

Is this wrong, and the current through each of these resistors is equal to IT?
 
Last edited:
  • #4
berkeman
Mentor
56,842
6,821
But it raises one question for me, you say the current is the same through all resistors, but as I understand, the resistance causes the current to drop.
No, as Edward says, the current is the same everywhere in the series circuit. That same current causes a different voltage drop in the different load resistors, and that same current flows through the power supply (battery).
 

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