What the Simulation Shows
The P = I²R simulation displays a live circuit diagram with four interactive elements that update in real time as students move two sliders:
The Circuit: A rectangular loop showing a battery (left side, green), a resistor with a zigzag pattern (top centre, orange), and an ammeter (bottom centre, blue). Electrons — shown as blue dots labelled with a minus sign — travel around the loop, visibly speeding up as current increases.
The Sliders: One controls Current (I) from 0.5 to 10 A, the other controls Resistance (R) from 1 to 50 Ω. Both update everything on screen instantly.
The Readout Panel: Shows the calculation working step by step in bright white — P = I² × R, then the substituted values, then the squared step — so students can see exactly how the number is built up. Below that, a large purple Watts figure shows the final answer, and a gradient heat bar fills from left to right as power increases.
The Glow Effect: The resistor on the circuit diagram glows orange-red when power is high, giving a visceral sense that energy is being wasted as heat — the glow grows with power.
The Insight Bar at the bottom changes message depending on conditions, flagging when current is dangerously high, when resistance is very large, or reinforcing the key concept that doubling current quadruples power.
Suggested Classroom Activity
Topic: Power in electrical circuits — P = I²R Level: GCSE Physics (Year 10/11) Duration: 25–30 minutes Group size: Pairs
Starter (5 min)
Write on the board: “Which is more dangerous — doubling the current or doubling the resistance?” Ask students to vote with hands or mini whiteboards before they touch the simulation. Record the class split. Tell them they’ll find out who was right by the end.
Guided Investigation (15 min)
Give students this structured task:
Part A — Explore resistance alone Set current to 3 A. Slide resistance from 1 Ω to 50 Ω. Record power at R = 10, 20, and 40 Ω.
- What happens to power as R doubles? Is the relationship linear?
- Watch the heat bar. What does this tell you about where energy goes?
Part B — Explore current alone Reset resistance to 10 Ω. Slide current from 2 A to 4 A to 8 A.
- What happens to power each time you double the current?
- Why does the glow on the resistor grow so dramatically?
Part C — The key comparison Set I = 5 A, R = 10 Ω. Note the power. Now try doubling R to 20 Ω (reset I to 5 A). Then try doubling I to 10 A (reset R to 10 Ω).
- Which change caused a bigger rise in power, and by how much?
Results Table (on paper or whiteboard)
| I (A) | R (Ω) | I² | P = I²R (W) |
|---|---|---|---|
| 2 | 10 | 4 | 40 |
| 4 | 10 | 16 | 160 |
| 8 | 10 | 64 | 640 |
| 4 | 5 | 16 | 80 |
| 4 | 20 | 16 | 320 |
Students complete the I² column themselves before checking with the simulation — this reinforces why squaring matters.
Plenary (5 min)
Return to the opening vote. Ask a student to use the simulation to prove which is more dangerous: doubling current vs doubling resistance. Then pose the exam-style question verbally:
“A resistor carries a current of 3 A and has a resistance of 8 Ω. Calculate the power dissipated.”
Students write the answer on mini whiteboards, then verify with the simulation.
Real-World Links to Mention
- Household fuses blow when current gets too high — P = I²R explains exactly why the wire melts
- Power lines use very high voltage and very low current specifically to reduce I²R losses over long distances
- Laptop and phone charger cables get warm — that warmth is wasted power, calculated by this exact formula