Series circuits · Grade 8
In Grade 8 you learn: series circuits: one loop; current in series.
In a series circuit everything is in one loop. The same current flows everywhere, the supply's p.d. is shared between the components, and the resistances add up. If one part breaks, the whole loop stops.
Key facts
- Series: same current everywhere; p.d.s add up to the supply; R_total = R₁ + R₂ + …
- If one bulb breaks in series, the loop is broken and all the bulbs go out.
- Cells in series, facing the same way, add their p.d.s: two 1.5 V cells give 3 V.
Worked examples
Example 1
Three lamps are in series with a cell. The ammeter next to the cell reads 0.2 A. What do ammeters placed between the lamps read?
Answer: 0.2 A everywhere
Example 2
One bulb breaks in a series circuit of three bulbs. What happens to the other two?
Answer: They go out too.
Example 3
A switch is opened in a series circuit with two lamps. Which lamps go off?
Answer: Both lamps go off.
Example 4
Two 1.5 V cells are joined in series, facing the same way. What is their total p.d.?
Answer: 3 V