🎒 What you need

a torch, phone light or candle and a hand to block it
someone to keep a steady beat by clapping
chalk and paper

✋ Do this

Beat time steadily, one beat per second. Turn the torch on for one beat, off for one beat, repeatedly. That is 50 percent duty cycle.
Now do on-on-on-off. That is 75 percent. Draw both patterns as filled and empty boxes on the ground.
Speed up until you are flicking several times per second. Look at the light out of the corner of your eye — it starts to look dim rather than flashing.
Try 25 percent fast. It looks dimmer still. You are controlling brightness with a switch that has no dimmer at all.
Write the formula yourself: average power equals duty cycle times full power. Check it against what you saw.
Last: flick slowly on purpose. The flicker returns. That is why PWM frequency matters as much as duty cycle.

💡 Why it works

This is pulse width modulation, and it is how nearly every motor speed and LED brightness is controlled in real electronics. Transistors are efficient when fully on or fully off and waste energy in between, so instead of throttling the current you switch it rapidly and vary the on-time. A motor's own inertia smooths the pulses the same way your eye smoothed the torch.

🔥 Challenge

Two of you flick torches at different duty cycles at the same speed. Can a third person rank them by brightness without being told the numbers? Test whether people can tell 60 from 70.

📖 New words

PWMpulse width modulation: switching fast and varying the on-time to control power

duty cyclethe percentage of each cycle the switch spends on

frequencyhow many complete on-off cycles happen per second

💡

Pulse Master

Tap when you have finished this module.