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Grades 8–10 Intermediate About 20 min Version 1 Awaiting review Premium

Series and parallel circuits

In a series circuit the components are joined one after another, so there is only one path: the same current flows through each, and the battery's voltage is shared between them. Resistances in series add: R = R₁ + R₂ + …. In a parallel circuit each component is on its own branch, so each gets the full battery voltage and the currents in the branches add up. For resistances in parallel, 1/R = 1/R₁ + 1/R₂ + …, so the total resistance is less than any one branch. House wiring is in parallel so each light can be switched on and off by itself.

What you will learn

  • Compare the brightness of bulbs in series and in parallel.
  • Explain what happens when one bulb is removed from each kind of circuit.
  • Calculate equivalent resistance for series and parallel combinations.

Before you start

  • Know that current is measured in amperes and resistance in ohms.

Materials

  • 6 V battery pack
  • Three bulbs in holders (6 Ω each) and a 12 Ω bulb

Equipment

  • Ammeter and connecting wires

Procedure

  1. Join two bulbs in series to the 6 V battery and record the current and brightness.
  2. Join the same two bulbs in parallel and compare.
  3. Take bulb A out of each circuit and record what happens to the others.
  4. Use three bulbs, and change bulb B to 12 Ω, and calculate the total resistance each time.

How this simulation is simplified

  • The battery gives a steady 6 V; the bulbs keep a fixed resistance and the wires have none.
  • Brightness is shown relative to one 6 Ω bulb across the full 6 V (6 W).