- Created by: Charlottelg
- Created on: 18-11-18 13:15
Charge doesn’t ‘leak away’ - it’s conserved
Charge flows - doesn’t get used up or lost.
Whatever charge flows into a junction will flow out again.
Current = rate of flow of charge, it follows that whatever current flows into a junction = same as current flowing out.
Kirchhoff’s first Law - The total current entering a junction = the total current leaving it.
Energy is conserved too
Energy is conserved.
Electrical circuits - energy is transferred round circuit.
Energy transferred to a charge = e.m.f, energy transferred from a charge = p.d
Closed loop - these two quantities must be equal if energy is conserved.
Kirchhoff’s second law - The total e.m.f around a series circuit = the sum of the p.d.s across each component.
Exam questions might get you to combine resistors
1. Same current at all points of circuit (as there are no junctions)
2. E.m.f split between components (Kirchoff’s second law) so: ε = V1 + V2 + V3
3. V = IR, so if I is constant: IR total = IR1 + IR2 +IR3
4. Cancelling the Is gives: R total = R1 + R2 + R3
5. As R = 1/G, you can write this in terms of conductance: 1/G total = 1/G1 + 1/G2 + 1/G3
1. Current is split at each junction so:cI = I1 + I2 + I3
2. Same p.d across all components (three separate loops-within each loop e.m.f = sum of individual p.d.s)
3. So V/R total = V/R1 + V/R2 + V/R3
4. Cancelling the Vs gives: 1/R total = 1/R1 + 1/R2 + 1/R3
5. As R = 1/G, you can write this in terms of conductance: G total = G1 + G2 + G3