Unplugging a Running Hair Dryer Briefly Creates Thousands of Volts
The outlet supplies only a few hundred volts, but the collapsing magnetic field inside the dryer momentarily supplies the thousands needed to electrify air.
Veritasium · AD - Why do I get this spark when I unplug my hair dryer?Pull the plug on a running hair dryer and you may see a small, bright spark jump between the plug and the socket. That flash should be impossible, because making even a one centimeter spark in air takes about 10,000 volts, while the outlet supplies only around 120 to 240 volts.
The extra voltage comes from inside the dryer itself. While the dryer is running, electric current flows through coils of wire, the loops that help power the heat and the fan. That flowing current also builds an invisible magnetic field around the coils.
The trouble starts when you yank the plug. You cut that current off suddenly, so the magnetic field collapses very quickly toward zero.
Nature resists such an abrupt change. As the field falls, it briefly acts like a generator and creates, or induces, its own voltage in the coil, pushing to keep the same current flowing.
For an instant, that push becomes enormous, thousands of volts. It is strong enough to electrify the tiny gap of air where the prongs leave the outlet, turning normally insulating air into a pathway for current. That sudden jump of current through the air is the spark you see.
In other words, your wall outlet did not supply the spark. Your unplugged dryer did, one last gasp from its dying magnetic field.
Questions people ask
Is that unplugging spark dangerous?
Yes, small sparks from unplugging are generally normal and not a sign your house wiring is failing. They are brief and happen right at the plug, but if you see large flashes, browning around outlets, or sparks while simply plugging something in, have an electrician check it.
Why does it happen only when the appliance is running?
Usually not with modern dryers, phones, and laptops that are switched off, because there is little or no current flowing through their coils and therefore little magnetic energy to release. The flash is most likely when you interrupt an appliance while it is actively drawing power.
What does it mean to ionize the air?
Ionize means to strip electrons off air molecules so the air can conduct electricity. Normally air is an insulator, but a high enough voltage tears its molecules apart into charged particles, creating a glowing, conductive path that the current can jump across.