Of course, we’re so used to the slim machines we enjoy today that we often forget how big laptops used to be. Miniaturisation has done wonders. Even as our devices have gotten smaller, slimmer and lighter, they are faster and have better battery life (at least when they are new!)
But that comes at a cost. More components are combined, and squeezed together. The insides of a modern laptop, phone or tablet are a marvel of packing. We all wish we could pack the boot of the car so tightly when we travel!
All this means that there is little scope for cooling. As the components get hot, they need somewhere to vent heat to. On laptops, there are often heat vents but these can get blocked. That’s especially true if its resting on something that’s not smooth – like a towel or blanket. One common cooling system is to transfer heat to the case, then let the atmosphere cool it. Of course, that means that the case gets warm, and in winter especially, its very noticeable.
But none of that answers why the components get warm. That of course is physics. When a current flows through a wire, the wire heats up. The electrons in the cable move, and that movement generates heat. That is how heater elements work on your old electric heater, and of course basically how the filament in an old light-bulb works. The thinner the wire, (technically, the more resistance in the wire) and the more current flowing, then the hotter it gets. If it gets too hot, it can catch fire.
Laptops are of course full of micro-components, and the circuits within the components draw a current, which means there is a flow through the microscopic wires. The good news is that the amount of current is infinitesimal, which is also why batteries last so long. But the physics can’t be denied and ultimately, if its working, then power is flowing, and the components will get warm or even hot.
Actually, there is one component that gets really hot, and that is the battery. They have internal resistance, which means that when they charge or discharge, the flow of current causes heat to build up.
In simple terms, the more work a device does, the more current that flows, and more current means more heat. When we want devices to charge quickly, we do it with lots of current (amps) and that creates heat.
If the machine does less, then it draws less charge (so the battery also lasts longer) and it doesn’t heat up so much. Some software we use makes a device work harder, for example GPS/location apps, and the impact will be obvious.
So, on your phone, tablet and laptop, always close apps you aren’t using. Be aware that turning on features, or turning up screens and colours uses more current and therefore heat. If you are low on battery, go into your settings, turn down the power and enjoy that precious few extra minutes as you search around for a powerpoint to plug into.