BuilderBuilding & Engineering🔬 Experiment

Build Three Working Circuits

Duration

3 sessions, 45-60 minutes each

Age

9-12

Format

Hands-on

Parent Role

Facilitate

Read

10 min

Safety

Yellow

Contents10 sections · 10 min
  1. 01Overview
  2. 02The Question
  3. 03Background
  4. 04Hypothesis
  5. 05Materials
  6. 06Procedure
  7. 07Analysis
  8. 08The Explanation
  9. 09Extensions
  10. 10Safety Notes

What You’ll Be Able To Do

Learning Objectives

  1. 1Build a complete electrical circuit that turns a real light on and off with a switch
  2. 2Construct a simple alarm that uses a circuit to trigger a buzzer when a door or drawer opens
  3. 3Wind and wire an electromagnet, then test how the number of coils changes its strength
  4. 4Explain in your own words what a closed circuit, a short circuit, and a conductor are

Ready When They Can

  • Can follow a multi-step plan and keep parts organized across a work session
  • Has the patience to test, fail, and adjust a connection that is not working
  • Can twist wires together or use a screwdriver on small terminals with steady hands
  • Understands that electricity flows in a loop and is curious about what makes a light turn on

Materials Needed

  • 4 AA batteries and one 4-AA battery holder (gives you 6 volts)
  • One 9-volt battery and a 9-volt battery clip with leads (for the electromagnet)
  • Two 3-volt LED bulbs OR two small 3V-6V flashlight bulbs with holders
  • One small 6V buzzer or piezo buzzer
  • A spool of insulated hookup wire, 22-gauge (about 10 feet)
  • Wire strippers (or an adult with a utility knife to strip wire ends)
  • Electrical tape
  • One small toggle switch or push-button switch (optional — you can also use bare wire ends)
  • Aluminum foil (for a homemade switch)
  • A 3-inch iron bolt or large iron nail (for the electromagnet)
  • A pile of steel paperclips or small steel washers (to test magnet strength)
  • A clothespin and two thumbtacks (for the alarm trigger)
  • A notebook and pencil for recording results
  • Optional: a multimeter to measure voltage

Build Three Working Circuits

Overview

You are going to make electricity do three jobs: light a bulb, sound an alarm, and turn a plain iron bolt into a magnet strong enough to pick up paperclips. None of these are tricks or toys with the work hidden inside a plastic box. You build the whole thing, wire by wire, and you will be able to see exactly why it works. By the end you will understand the one idea that runs underneath every electrical device in your house: electricity only does work when it can travel all the way around a loop and back.

The Question

Every circuit you build answers the same question in a different way: What does it take to make electricity flow, and what can you make it do once it flows?

More specifically, you are testing three things:

  1. Can I control a light by opening and closing a loop?
  2. Can I use a loop that breaks when something moves to make a sound?
  3. Can I turn electricity into magnetism, and does adding more wire make the magnet stronger?

Background

Electricity is the movement of tiny charged particles called electrons. A battery is like a pump — it pushes electrons out of one end (the negative terminal), and they will travel through anything that lets them pass, all the way around, and back into the other end (the positive terminal). That round trip is called a circuit.

Three words you need before you start:

  • Closed circuit: the loop is complete, electrons flow, and your device works. A light switch turned ON closes the circuit.
  • Open circuit: there is a gap in the loop, electrons cannot cross it, and nothing happens. A switch turned OFF opens the circuit.
  • Short circuit: the electrons find a shortcut back to the battery without passing through your device. This is dangerous — the wire heats up fast because all the energy has nowhere useful to go. You will learn to spot and avoid this.

A conductor is a material electrons move through easily — metal, especially copper. An insulator is a material that blocks them — the plastic coating on your wire, rubber, dry wood. The whole craft of wiring is putting conductors where you want electrons to go and insulators everywhere else.

Hypothesis

Before you begin, write down what you think will happen and why:

"I think the electromagnet with more coils of wire will be _______ than the one with fewer coils, because _______."

Also predict: How many paperclips do you think your strongest electromagnet will pick up? Write the number down now. You will check it later, and it is more fun when you committed to a guess first.

Materials

See the materials list in the frontmatter above. Before Session 1, lay everything out on a tray or in a shallow box so parts do not roll away. Strip about half an inch of plastic off both ends of six pieces of wire, each about 8 inches long. If you have wire strippers, this is your job. If you only have a utility knife, an adult does the stripping — knife work toward a child's fingers is not worth the risk.

Procedure

Setup

  1. Clear a flat table with good light. No water nearby, no metal jewelry on your hands.
  2. Put the batteries in the holder. Do not connect anything to the holder yet — leave the two leads apart.
  3. Lay your three projects out as three separate stations so you do not mix up parts: Light, Alarm, Magnet.

Experiment Part 1: The Light Circuit (Session 1)

  1. Take the battery holder. It has two wires coming out — one red (positive), one black (negative).
  2. Connect the black wire to one leg of your bulb holder (or one leg of the LED). Twist the bare ends together and tape the joint.
  3. Take a fresh piece of wire. Connect one end to the other leg of the bulb. Leave the other end loose for a moment.
  4. Touch that loose end to the red wire of the battery holder. The bulb lights. You just closed the circuit.
  5. Pull the wires apart. The bulb goes dark. That is an open circuit.
  6. Now build a switch you control. Cut the wire between the bulb and the battery and add a toggle switch in the gap (connect one wire to each terminal of the switch). Or make a homemade switch: tape two strips of aluminum foil down with a small gap between them, and bridge the gap with a paperclip you can swing across. Flip the switch on and off and watch the bulb obey.

LED note: LEDs only work one direction. If yours does not light, swap the two wires on the LED and try again.

Experiment Part 2: The Alarm (Session 2)

  1. This circuit uses a buzzer instead of a bulb, and a special switch that is normally OPEN and snaps CLOSED when something moves.
  2. Build the trigger: push a thumbtack into each jaw of a wooden clothespin so the two tacks touch when the clothespin is clamped shut. Wrap a wire around each tack.
  3. Wire the circuit: battery → buzzer → one trigger wire → (through the clothespin tacks) → other trigger wire → back to battery.
  4. Clip the clothespin onto the edge of a drawer with a small card of cardboard slipped between the jaws so the tacks are held APART. The circuit is open, the alarm is silent.
  5. Tie a string from the cardboard to the inside of the drawer. When someone opens the drawer, the string yanks the cardboard out, the clothespin snaps shut, the tacks touch, the circuit closes, and the buzzer screams.
  6. Test it. Reset it. Test it again. Catch a sibling.

Experiment Part 3: The Electromagnet (Session 3)

This is the experiment with real data to collect, so slow down and be exact.

  1. Take your iron bolt. Starting near the head, wrap insulated wire around it in tight, neat coils — all turning the same direction. Wind exactly 25 turns. Leave a few inches of wire free at each end. Strip those ends.
  2. Connect the two stripped ends to the 9-volt battery clip.
  3. Snap the clip onto the 9-volt battery. Do not leave it connected for more than 15-20 seconds at a time — the wire and battery get hot.
  4. Quickly touch the bolt to your pile of paperclips. Count how many it lifts. Record it. Disconnect.
  5. Let the battery rest a minute. Now add more coils — wind up to 50 turns total. Reconnect, test, count, record. Disconnect.
  6. Wind up to 75 turns. Test, count, record, disconnect.

Record

Number of coils Paperclips lifted (trial 1) Paperclips lifted (trial 2) Average
25
50
75

Also sketch each of your three circuits in your notebook. Draw the loop and mark where the gap (the switch) is. A builder who can draw a circuit understands it.

Analysis

  • What happened to the magnet's strength as you added coils? Did your numbers go up, down, or stay the same?
  • Did the result match your hypothesis? If you guessed a paperclip count earlier, how close were you?
  • When the light or buzzer did NOT work the first time, what was usually wrong? (For almost everyone, it is a loose connection or a wire touching where it should not.)
  • What would you change to make the magnet even stronger without adding coils? (Think about the battery, and think about the bolt.)

The Explanation

Read this after you have done the experiments and written your own analysis.

The light and the alarm are the same idea wearing two costumes. Both are loops. The only difference is the switch. The light's switch is one you control on purpose. The alarm's switch is one that something else closes for you — a moving drawer. Engineers call a switch that closes when triggered a "normally open" switch, and almost every alarm, doorbell, and motion sensor in the world is built on exactly this trick.

The electromagnet reveals something deeper: electricity and magnetism are two faces of the same force. When electrons flow through a wire, they create a magnetic field around that wire. A single straight wire makes a weak field. But when you coil the wire, every loop's field stacks on top of the next one, all pointing the same way. More coils means more stacking means a stronger magnet. Wrapping the coil around iron makes it stronger still, because iron concentrates the magnetic field. This is not a toy effect — it is exactly how the motors in your fans, your car's starter, and the speakers playing your music all work. Cut the current and the magnetism vanishes, which is what makes electromagnets so useful: you can turn them on and off.

Extensions

  • Change one variable: Keep the coils the same but swap a 9-volt for two 9-volts wired in a line (in series). Does more voltage mean a stronger magnet? Test it carefully and briefly.
  • Real-world connection: Visit a scrapyard or watch a video of a crane lifting cars with an electromagnet. It is your 75-coil bolt, scaled up ten thousand times. Notice that the operator drops the cars by flipping a switch — same open circuit you built on day one.
  • Further reading: Look up how Joseph Henry and Michael Faraday discovered electromagnetism in the 1820s and 1830s. They wound their coils by hand, exactly like you did.

Safety Notes

This experiment is rated yellow — an adult facilitates and stays present, especially during wire stripping and any time the electromagnet is connected.

Chemical/Material Hazards

  • Heat from short circuits and electromagnets. The electromagnet draws a lot of current and the wire, the bolt, and the 9-volt battery will get warm to hot within seconds. Never leave the electromagnet connected longer than 20 seconds. Disconnect between every test. If anything gets too hot to touch comfortably, disconnect immediately and let it cool.
  • Use only the batteries listed. Never connect this to a wall outlet, a car battery, or any household power. Household voltage can injure or kill. This project lives entirely on small batteries for a reason.
  • Never connect a battery's two terminals directly to each other with a bare wire and nothing in between. That is a short circuit — the wire heats up fast and the battery can leak or rupture. Always have a bulb, buzzer, or coil in the loop.
  • Battery care. Do not mix old and new batteries. Remove batteries from holders when you finish for the day so nothing drains or warms up unattended. If a battery is bulging, leaking, or hot, an adult disposes of it.

Disposal

  • Used batteries go to a battery recycling drop-off (many hardware and grocery stores have a bin), not the regular trash.
  • Wire scraps and tape go in the trash. Coil leftover wire neatly to reuse.

Protective Equipment

  • No goggles needed, but tie back long hair and remove rings, bracelets, and metal watches — metal jewelry can complete a short circuit across your skin and get hot.
  • Keep the workspace dry. Wet hands and electricity do not mix, even at low voltage.
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