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Series and parallel circuits lab: both on one breadboard

This series and parallel circuits lab puts both wirings on one breadboard, so students can see the difference in brightness first and then find it with a meter.

Ages 12 and up, first circuits unit. About 45 minutes. No code.

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The lesson

Objective and parts

By the end, students can

  • Tell a series connection from a parallel one on a breadboard and on a schematic.
  • Show that parts in series share the voltage and carry the same current.
  • Show that parallel branches each get the full voltage and their currents add.

Parts, already on the bench

  • A 5 V supply (an Arduino Uno used only for its 5 V pin)
  • Four red LEDs
  • Three 220 ohm resistors
  • A multimeter in series with the series pair

Nothing to hand out or collect: the circuit opens built and wired.

Steps

What students do

Each step is short enough to read out. Students work in the simulator beside this page.

Open this lab
  1. Open the lab and press Run. All four LEDs light. Which pair is dimmer?
  2. Read the meter in the series string: about 8 mA through both LEDs and their one resistor.
  3. Set the meter to DC volts and measure across each series LED. Each has about 1.6 V.
  4. Measure across one LED in a parallel branch, then across its resistor.
  5. Work out the current in one parallel branch from the voltage across its 220 ohm resistor.
  6. Delete the wire to one LED in the series string and watch the other one. Undo, then do the same to one parallel branch.
Questions

Questions for students

Hand these out as they are. The expected answers are under the list, for you.

  1. Why is the series pair dimmer than the parallel pair?
  2. One series LED is removed. What happens to the other, and why?
  3. One parallel branch is removed. What happens to the other?
  4. How much current does the whole parallel pair draw from the supply?
  5. Are the lights in your home wired in series or in parallel? How do you know?
Answer key for the teacher
  1. Two LEDs in a row use up more of the 5 V, which leaves less across the resistor, so less current flows: about 8 mA against about 14 mA in each parallel branch.
  2. It goes out. There is one path, and it is now broken.
  3. Nothing changes. Each branch has its own path from 5 V to ground.
  4. About 28 mA: the two branch currents added together.
  5. In parallel. One lamp can be switched off or fail without the others going out, and every lamp gets the full supply voltage.
Go further

For students who finish early

  • Move the meter into one parallel branch and check the predicted current.
  • Give the series string a third LED and explain what you see.
Your class

Give this lab to every student

Assign to my class puts this circuit on each student’s class page as a starter. They change their own copy and hand it in, and the work comes back to you in one list.

The class tools are free for 30 days for one class of up to 20 students, with no card. Opening and running the lab needs no account and stays free.

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