What the Simulation Shows – AC VS DC
The AC vs DC simulation displays a live circuit with two modes that students can switch between using the DC and AC toggle buttons at the top. Every part of the screen updates instantly when you switch.
The Circuit: A rectangular loop with a source on the left and a light bulb on the right. In DC mode the source is shown as a battery with + and − terminals; in AC mode it becomes a circle with a sine wave drawn inside, representing a mains supply. Direction arrows sit on each wire segment showing which way current is flowing at any moment.
The Electrons: Amber dots in DC mode travel steadily around the loop in one direction — always the same way, at constant speed. In AC mode the cyan dots slow down, stop, and reverse 50 times per second, visibly oscillating back and forth rather than circulating.
The Bulb: In DC mode it glows with a constant steady amber light, reflecting the unvarying current. In AC mode the glow pulses — brightening and dimming rhythmically as the current rises and falls through each half-cycle. The filament and surrounding glow both respond to the instantaneous current value.
The Waveform Panel: Plots voltage against time in real time. DC produces a flat horizontal line held above zero — constant and unwavering. AC traces a smooth sine wave that crosses zero repeatedly, rising positive then falling negative, illustrating the alternating nature of the current.
The Info Panel updates with each mode switch, showing the current type, direction of flow, UK mains frequency (50 Hz for AC, not applicable for DC), and a plain-English fact. The footer bar also changes to give a real-world context clue.
Suggested Classroom Activity
Topic: AC and DC — sources, waveforms, and real-world use Level: GCSE Physics (Year 10/11) Duration: 20–25 minutes Group size: Pairs or individuals
Starter (4 min)
Hold up a phone charger and a AA battery. Ask: “Both of these supply electrical energy — so what’s actually different about them?” Take a few answers, then say: “By the end of this activity you’ll be able to explain exactly what’s different, using evidence from the simulation.”
Guided Exploration (12 min)
Give students this sequence to work through:
Step 1 — Observe DC. Start in DC mode. Watch the electrons and the bulb for 30 seconds. Sketch the waveform shape. Write one sentence describing what the current is doing.
Step 2 — Observe AC. Switch to AC mode. Watch for 30 seconds. Sketch the waveform. How is the electron movement different? How does the bulb behave differently?
Step 3 — Compare. Complete this table on paper:
| Feature | DC | AC |
|---|---|---|
| Direction of flow | ||
| Waveform shape | ||
| Bulb brightness | ||
| UK mains frequency | ||
| Example source |
Step 4 — Predict. Without switching modes, ask: “If you doubled the AC frequency, what would the waveform look like? What would you notice in the bulb?” Discuss with your partner before checking the info panel.
Key Questions to Discuss
- Why does the AC bulb not actually flicker visibly in real life, even though current reverses 50 times a second?
- Why is AC used for mains electricity rather than DC? What does it allow engineers to do?
- Your phone runs on DC internally — but the mains supply is AC. What must the charger be doing?
Plenary (5 min)
Return to the starter objects — the charger and battery. Ask a student to narrate what’s happening inside each one using the words: alternating, direct, frequency, waveform, reverses. Use the simulation on the board to verify each point as they speak.
Real-World Links to Mention
- The UK mains supply is 230 V AC at 50 Hz — the simulation models this exactly
- Batteries, solar cells, and fuel cells all produce DC — steady and one-directional
- AC won the “War of Currents” in the 1880s between Edison (DC) and Tesla/Westinghouse (AC) because transformers can step AC voltage up for efficient long-distance transmission
- Inside every phone charger is a rectifier circuit that converts AC to the DC your battery needs