in Electric Circuits Current in a series circuit The current is the same at every point along the wire in a series circuit.
Current in parallel circuits
Different-sized currents can flow through parallel parts of a circuit, but the size of the current entering the junction before the circuit divided and after the parallel parts of the circuit join up again is the same.
I1 I I2 I3 R1 Rules for currents and voltages in circuits R2 R3
Fig 18.3: Sum of currents entering a junction equals the sum of currents leaving the junction
The sum of the currents entering a point in a circuit equals the sum of the currents leaving it (Fig 18.3).
(I I1 I2 I3 .. .)
The potential difference of the full circuit equals the sum of all the potential differences in the circuit (Fig 18.4). (V V1 V2 V3 .. .)
V
RESISTORS IN SERIES
R R1 R2 R Total resistance
R1 Resistance 1 R2 Resistance 2
RESISTORS IN PARALLEL
1 R 1
R1
1 R2
R Total resistance
R1 Resistance 1 R2 Resistance 2
V1 V2 V3
Fig 18.4: Sum of voltages across a series of individual resistors is equal to the voltage across all the resistors
Calculating resistance in circuits
The ability to use these equations is required for both higher and ordinary level, while their derivations are for higher level only. Resistors in series
R R1 R2 DERIVATION OF FORMULA R R1 R2
Derivation: Based on: The two resistors are connected in series, so that the same current, I, flows through both. [since :Ohm’s law] [by dividing by I ]
