Kirchhoff's Second Law
Kirchhoff's Second Law
- A source gives energy to charge. Components transfer that energy to other stores.
- After one complete trip around a loop, the total energy gained per coulomb equals the total energy transferred per coulomb.
Energy around one complete loop
Definition
1 markWhat is meant by Kirchhoff's second law?
Model answer: Around any closed loop, the sum of the e.m.f.s equals the sum of the potential differences.
The first law conserves charge at a junction. The second law conserves energy around a loop.
Keep one direction and one sign convention
- Choose a direction around the loop and keep it.
- Across a cell from its short line to its long line, count a positive e.m.f. Crossing the other way gives a negative e.m.f.
- Across a resistor in the direction of current, count a drop of .
Worked example
Two opposing cells
A 6.0 V cell opposes a 2.0 V cell in a loop containing 10 Ω and 30 Ω resistors. The net e.m.f. is 4.0 V and the total resistance is 40 Ω, so .
Your turn9702/12/O/N/24 Q36
State the conservation principle represented by Kirchhoff's second law. [1] (9702/12/O/N/24 Q36)
Show worked answer
Conservation of energy.