Science Fenns K-5Grades K to 5
A battery, a bulb and two wires laid out on a table forming a loop with the bulb lit.

Science / All lessons / Energy, Circuits and Light

What a Circuit Needs

Source, path, load, and a closed loop.

Lesson 19 of 41

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Before we start

Today’s story

What a Circuit Needs

A bulb stays dark until the path is complete. Make the path and it lights. Break it and it goes out.

A circuit has a source, which is the battery. It has a path, which is the wires. It has a load, which is the bulb. And the loop must be closed.

Electric energy only flows in a complete circuit. Let us build one.

See it

Five steps. Every time.

    Hands on

    Light the Bulb

    25 minutes · Do this with a grown-up nearby

    You need

    • One D or AA battery
    • Small flashlight bulb
    • Two wires with bare ends
    • Tape
    • Switch from a clothespin and foil

    Do this

    1. Touch the bulb base to the battery bottom.
    2. Touch the bulb side to the battery top with a wire.
    3. Tape the pieces so they hold.
    4. Open the loop by lifting one wire.
    5. Add a clothespin switch.
    6. Draw your loop with arrows.
    Write or draw: A drawing of your working circuit with labels for source, path and load.

    Watch for: What happens when the loop is cut? Does the bulb need both wires touching?

    Safety: Use only a small battery and never use outlets.

    Same every time

    Three rules

    Rule 1Close the loop

    No loop, no current.

    Rule 2Use only small batteries

    Wall power is dangerous.

    Rule 3Check connections

    A loose wire can break the path.

    Grandpa Fenn’s notebook

    Say it like a scientist

    circuit
    A complete path for electric current.
    load
    The part that uses the energy, like a bulb.
    switch
    A part that opens or closes the path.
    source
    The part that supplies the push, like a battery.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • How do you know the loop is closed?
    • Where do you flip a switch at home?
    Did you know

    Electric charge moves in a circuit, yet the wires never run out of it.

    Someone who does this

    An electrician checks circuits so a building is wired safely.

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