How do computers and electronics produce heat?
In: 7
Wires have resistance. That means they heat up whenever electricity flows through them.
A computer basically implements 0’s and 1’s using a huge number of switches. Basically all modern computers wire their switches using the “CMOS logic” strategy, which stands for “Complementary MOS.” MOS describes what the switch is made of (Metal Oxide Semiconductor). Complementary means every point in the circuit that represents a 0 or a 1 is wired to a pair of switches which connect directly to the – and + terminals of the power supply. If the point is supposed to be a 0, the first switch connects it to the – terminal and the second switch disconnects it from the + terminal, and it’s 0V. (The reverse happens if the point is supposed to be a 1, and it takes the + terminal voltage; traditionally 5V, but usually 3.3V or lower in newer devices).
If you draw a CMOS circuit on paper, it looks perfectly efficient because the power supply terminals are never connected to each other, so no current flows and there’s no way for it to heat up. Unfortunately the paper drawing makes a few assumptions that don’t apply to switches and wires you can build in the real world with tools and materials we have:
– (1) Real switches can’t switch infinitely fast.
– (2) Real switches sometimes act “half-open half-closed” while they’re switching and let electricity through.
– (3) Real switches sometimes let a tiny bit of electricity “leak” through even when they’re “supposed” to be fully open, and this problem gets worse the more you try to make the switches small and fast.
– (4) The sections of wire you’re trying to use as points that represent 0 or 1 have non-zero “capacitance,” basically you don’t change voltage just by being connected to a power supply terminal; the power supply needs actually to push or pull a few electrons into or out of the metal to actually change its voltage.
– (5) The wires you’re using have non-zero “inductance,” basically there’s a sort of “momentum” and you get energy wasted by the electronic equivalent of [that sound pipes sometimes make when you shut off a faucet](https://www.youtube.com/watch?v=xoLmVFAFjn4).
– (6) The wires have non-zero resistance so all these currents cause stuff.
Think for a minute about your phone. It’s about a billion switches, switching about a billion times a second, jammed in a tightly packed case with no fans or wide-open paths to create airflow, the case is made of plastic (an insulator) and placed in a cloth pocket (another insulator), right next to a warm human — It’s a *freaking miracle of engineering* that your phone doesn’t melt itself.
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