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Originally Posted by micondie
The reason a piece of wood won't get hot is that there is no current flowing through it to generate any.
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Yes, that's exactly my point. You don't have as much current flowing through a resistor (V = IR, remember?), so less energy flow, so no heat. But don't take my word for it, look at a basic electric/electronics text, or put a temperature probe on one of those resistors that are supposed to be turning energy into heat.
Oh, and another question for thought: how come the wires in your toaster or electric heater - or indeed, the tungsten filament in an incandescent light bulb - are made of metal, which has a low resistance? Just for the heck of it, I dug out a few old incandescent bulbs, and measured their resistance: 40 W = 30 ohms, 60 W = 17 ohms, 75 W = 13 ohms. Not high resistance at all (though of course it increases with temperature), yet lots of heat.
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Why do you think they mount power transistors on a heat sink?
Why is your CPU mounted on a heat sink with a fan?
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Remember the transistor is a semiconductor. It's generating heat when current is flowing, and that's when it's in its lower resistance start.