Wirebook › Bonus lesson
Why do phones and computers get hot?
Play a big game for a while and your phone gets warm. Leave it on a sunny car seat and it might even refuse to work. Nothing is on fire: every gadget turns the electricity it uses into heat, and it has to get rid of that heat somehow. Here you can heat up a pretend phone, tug a pretend blanket to feel what insulation does, watch the phone protect itself, see why going a little slower cools a chip a lot, then play detective and cool seven overheating laptops.
Where does the heat come from?
The chip inside a phone (its processor) is made of billions of microscopic switches. Every time one flips between on and off, a tiny bit of electricity squeezes through and turns into heat, just like a toaster wire but far smaller. A big game flips them billions of times a second, so a phone playing one can make several watts of heat: about as much as a small bike light, packed into something thinner than a biscuit.
The battery adds some too. Pushing energy into a battery quickly, or pulling it out fast, warms it up. That's why a phone that is charging and running a game gets hottest of all.
How a phone protects itself
- It slows down (throttling). When the chip gets too warm, the phone turns its speed down. Because heat grows faster than speed, going a little slower cools it a lot. You notice it as a game getting jumpy.
- It charges more gently. Batteries wear out faster when they're hot, so a warm phone slows or pauses charging until it cools.
- It dims the screen and stops extras like the camera flash.
- As a last resort it shows a "too hot" warning and stops almost everything until it has cooled down. That's the phone looking after itself, not breaking.
Phones have no fans, so the heat has to spread through the metal and glass into the air around them. That's why the air matters so much: a cool breeze carries heat away quickly, while a duvet, blanket or pocket traps it (that's insulation — slowing heat flow, the same reason a duvet keeps you warm in bed), and a car in the sun is already hotter than the phone is allowed to be.
Why the fixes work (and the one that doesn't)
- Air in, air out. A laptop's fan pulls cool air through holes, usually underneath, and pushes hot air out of the side or back. A duvet, cushion or lap squashes those holes shut, so the same fan moves far less air. That's why a hard table is so often the biggest single fix.
- Stop the heat at the start. A stuck program or a pile of forgotten video tabs keeps the chip busy for nothing. Capping a game at 60 pictures a second stops it drawing pictures the screen never shows, and because heat grows faster than speed, that cools it a lot.
- Some heat is only for a while. A brand-new laptop spends its first hour installing updates and copying photos. It's noisy, then it calms down by itself.
- Inside jobs. Fluff builds up in the thin metal fins the fan blows through, and after years the grey thermal paste between the chip and its cooler dries out. Cleaning should be done switched off, with a grown-up; new paste is a job for a repair shop.
- Never the fridge. Cold gadgets fill with tiny water droplets when warm air meets them, like a cold drink can in summer. Water and electronics don't mix.
Keeping your own gadgets comfy
- Don't charge or play under a pillow, duvet or blanket. Let it breathe — covers trap heat the same way they keep you warm.
- Never leave a phone or tablet in a hot car or on a sunny windowsill.
- If it gets hot while charging, take off a thick case and pause the game.
- If it says it's too hot, put it somewhere cool in the shade, not in the fridge. Sudden cold can make water droplets form inside.
- Laptops have fans with air holes: keep them on a table, not a cushion, so the holes stay clear.
Grown-up how-tos on Tooltern: laptop overheating and slowing down: what to do · phone getting hot while charging: what's normal · laptop plugged in but not charging