In a series circuit there is only one path. The current is the same everywhere. The supply potential difference is shared between components: V = V₁ + V₂. The total resistance is the sum: R = R₁ + R₂. If one lamp breaks, all go out.
In a parallel circuit each component has its own branch. The potential difference across each branch is the same as the supply. The total current is the sum of the branch currents: I = I₁ + I₂. Adding a resistor in parallel decreases the total resistance, because there are more paths for the current. Household lighting is wired in parallel so each light can be switched on and off on its own.
Worked example
Resistors of 4 Ω and 6 Ω are in series with a 5 V supply. What is the current?
- Total resistance = 4 + 6 = 10 Ω.
- I = V ÷ R = 5 ÷ 10.
Answer:The current is 0.5 A.
Key words
- series
- components in one loop; current is the same
- parallel
- components on separate branches; p.d. is the same
- total resistance
- series: add; parallel: less than the smallest
- branch
- one path in a parallel circuit
New questions every time.
NGSS-referenced: HS-PS2-6