In parallel circuits, electrical components are connected alongside one another, forming extra loops.
An electron will not pass through every component on its way round the circuit. If one of the bulbs is broken then current will still be able to flow round the circuit through the other loop. If one bulb goes out, the other will stay on. Since fewer electrons pass through any loop, they will find it easier to travel and the total resistance of the circuit will be lower than any of the individual resistors in the circuit.
Since there are different loops, the current will split as it leaves the cell and pass through one or other of the loops. An ammeter placed in different parts of the circuit will show how the current splits:
This is when:
Since energy has to be conserved, the energy transferred around the circuit by the electrons is the same whichever path the electrons follow. Since potential difference is used to measure changes in energy, the potential difference supplied is equal to the potential differences across each of the parallel components:
This is when:
When resistors are connected in parallel, we know that the potential difference across each resistor is the same but the current through each resistor adds up to the current through the supply. By having more resistors that are connected in parallel, the more current flows for the same potential difference. If more current flows for the same potential difference, then the resistance has gone down. Overall then, more resistors connected in parallel means less overall resistance.