Kirchhoff's Rules

Kirchhoff's Rules

By Rachel Wampler

Kirchhoff's Rules

• Junction Rule

  • Total current into a junction must equal the total current out of the junction

• Loop Rule

  • ​For a closed-circuit loop, the total of all the potential rises minus total of all potential drops equals zero

  • In other words, the total voltage of a loop is zero​

Kirchhoff's Reasoning Stategry

1. Draw the current in each branch of the circuit (flows out of the positive terminal of the battery)

   1. Choose any direction. You are wrong if you are getting a negative current.

2. Mark each element with a plus and minus signs at opposite ends to show potential drop.

   1. Current flows from + to - though a resistor

      1. If the current leaves the element at +, voltage rise

      2. ​If the current leaves the element at -, voltage drop

3. Apply​ junction rule and loop rule to get as many independent equations as there are variables

4. Solve the system of equations

Multiple Choice

Find the current through the circuit

• 91.7 μA

• 100 μA

• 27.3 μA

• 64.8 μA

Multiple Choice

Find the currents through each element.

• I₁ = 2.45 x 10^-5 A

  I₂ = 4.81 x 10^-4 A

  I₃ = 4.57 x 10^-4 A

• I₁ = 2.45 x 10^-4 A

  I₂ = 4.81 x 10^-5 A

  I₃ = 4.57 x 10^-4 A

• I₁ = 2.45 x 10^-4 A

  I₂ = 4.81 x 10^-4 A

  I₃ = 4.57 x 10^-5 A

• I₁ = 2.45 x 10^-5 A

  I₂ = 4.81 x 10^-5 A

  I₃ = 4.57 x 10^-5 A