# Conservation of Energy and Charge in Circuits

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What is Kirchoffs first law?
The total current entering a junction = the total current leaving it. (Charge doesn't get used up or lost)
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What is Kirchoffs second law?
The total e.m.f around a series circuit = the sum of the p.d's across each component.
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Equation for sum of resistors in a series circuit
Rtotal= R1 + R2 + R3
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Equation for sum of resistors in a parallel circuit
1/Rtotal = 1/R1 + 1/R2 + 1/R3
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If R1=15Ω R2=20Ω R3=12Ω in a parallel circuit what is the total resistance?
1/Rtotal = 1/15 + 1/20 + 1/12 =1/5 so Rtotal = 5/1 Ω = 5Ω
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If R1=5Ω R2=10Ω in a series circuit what is the total resistance?
Rtotal = 5 + 10 = 15Ω
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## Other cards in this set

### Card 2

#### Front

What is Kirchoffs second law?

#### Back

The total e.m.f around a series circuit = the sum of the p.d's across each component.

### Card 3

#### Front

Equation for sum of resistors in a series circuit

#### Back ### Card 4

#### Front

Equation for sum of resistors in a parallel circuit

#### Back ### Card 5

#### Front

If R1=15Ω R2=20Ω R3=12Ω in a parallel circuit what is the total resistance?

#### Back 