The Lights-On Challenge
Why does a torch light up when you press its switch? Watch, predict, then try the circuit yourself.
Toggle lip sync any time without losing your place. Mouth timing is approximate; narration stays the same.
Download video — lip sync off · Download video — lip sync on
The lesson pauses for a quick question and a safe virtual experiment. You can skip either.
Your takeaway
A closed path lets current flow. For an ideal resistor at constant temperature, I = V ÷ R. Change one thing at a time to discover the relationship.
This is a virtual low-voltage model, not instructions for testing household mains electricity. Real lamp resistance can change as it heats up.
Explain it in your words
A strong answer uses I = V/R: at unchanged voltage, doubling resistance halves current. Example: 6 V ÷ 6 Ω = 1 A; 6 V ÷ 12 Ω = 0.5 A.
This is a self-check guide, not an AI grade. Compare your explanation and improve it.
From this model to real life
A battery torch: pressing its switch completes the circuit. Opening the switch breaks the path, even when the battery is charged.
A useful comparison: with an ideal 6 Ω resistor, 3 V produces 0.5 A and 6 V produces 1 A. Voltage doubles, so current doubles — provided resistance stays the same.
A real incandescent bulb is different: its filament gets hot and its resistance rises. Our constant-resistance model teaches Ohm’s law; it does not predict the brightness or current of every real lamp.
Open your revision notes
- Current is the rate of flow of charge: I = Q/t, measured in amperes (A).
- Potential difference is energy transferred per unit charge, measured in volts (V).
- Resistance opposes current, measured in ohms (Ω).
- Use I = V/R. At fixed R, increasing V increases I. At fixed V, increasing R decreases I.
- Conventional current goes from the battery’s positive terminal around the external circuit to its negative terminal. Electron drift is in the opposite direction.
- Common trap: voltage is not current. A charged battery can provide voltage while an open switch prevents current.
Try explaining why a torch stays off when its switch is open. Then change only one slider in the experiment and predict the result before checking.