Solving Problems with Kirchhoff's Laws
- Kirchhoff’s laws can be used to solve simple circuit problems
Worked example
For the circuit below, state the readings of ammeters A1, A2 and A3.
Answer:
Step 1: Calculate the current through ammeter A1
- The 0.270 A and A1 are connected in series
- The current entering the cell must equal the current out of it at A1
- Therefore A1 = 0.270 A
Step 2: Calculate the current through ammeter A2
- From Kirchhoff's first law, the total current into a junction must equal the total current out of it
Step 3: Calculate the current through ammeter A3
- Applying Kirchhoff's first law again gives:
Worked example
For the circuit below, state the readings of the voltmeters V1, V2 and V3.
All the lamps and resistors have the same resistance.
Answer:
Step 1: Calculate the potential difference shown by voltmeter V1
- Kirchhoff's second law states that the sum of the three components is equal to the e.m.f of the supply
Step 2: Calculate the potential difference shown by voltmeter V2
- Applying Kirchhoff's second law to this loop
- Both lamps have the same resistance R and the same current I through them so they share the energy equally and have the same potential difference
Step 3: Calculate the potential difference shown by voltmeter V3
- Applying Kirchhoff's second law to this loop