Making a Circuit Light Up

Lab Brief #4

🎯 Your mission

Predict it first. Then prove yourself right (or wrong).

⚡ The twist

The opposite of what you expect is often what happens.

What you'll learn

A bulb lights only when there is a complete loop from one end of the cell, through the bulb, and back to the other end. Break the loop anywhere — a gap, a switch, a loose wire — and everything stops, not just the part after the break.

Key words

complete circuit
An unbroken loop that lets current flow all the way round.
switch
A component that deliberately breaks and remakes a circuit.

Make a hypothesis first

Predict: what happens if you double the force?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

cell
bulb and holder
connecting leads
switch

⚠️ Safety first

Use a single cell or low-voltage supply only — never mains electricity.
Disconnect the cell between changes so nothing overheats.

Step 1 of 4 · Read

Think about what you just learned: say what "complete circuit" and "switch" mean in your own words before you start.

Step 2 of 4 · Do

Build a circuit with a cell, wires and a bulb, then break it in three different places one at a time. Record what happens each time and draw the circuit with the standard symbols.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

A bulb lights only when the circuit is:

How sure are you?😐 maybe

Question 2 of 2

Opening a switch anywhere in a simple loop:

How sure are you?😐 maybe

Mind = blown

🔥 A bolt of lightning is 5 times hotter than the surface of the sun.

Nice work!

You got 0 of 2 right.

Next: Gravity Pulls Everything the Same Way All lessons

🎯

Next Smart Experiment

We'll pick an experiment that matches exactly how you're thinking right now.

✨ More to explore

🌍 Where you see this in real life: You use this every time you flip a light switch, ride a bike, or kick a ball.

🏆 Stretch challenge (try it this week): Time how long a small ball rolls down something, then change the slope and try again.

👨‍👩‍👧 For the dinner table: “Show me something at home that uses this kind of energy.”

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