Physics · Electricity. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
In a series circuit the components are in one loop. There is only one path, so the current is the same everywhere. The supply p.d. is shared between the components, and the component with the bigger resistance gets the bigger share. The resistances add up.
In a parallel circuit each component is on its own branch. Each branch has the full supply p.d. across it. The current from the supply splits, so the total current is the sum of the branch currents.
Adding another resistor in parallel gives the charge an extra path. More current flows from the same supply, so the total resistance goes down. It is always less than the smallest resistor.
Students mix values from different parts of the circuit in V = IR, for example the supply p.d. with the resistance of one resistor. Use the V, I and R that belong to the same component, or all three for the whole circuit.
Answer: 7.5 V
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