What undesired energy outputs do you get from electronic devices? Take a computer for example. Some of the electrical energy becomes light in the monitor and LEDs and some becomes mechanical energy in the hard drive and cooling fans. Those are all desired. Where does the rest of the energy go? I know some goes into heat, but is that all? Is some spent as electromagnetic energy created by current in the circuit board? Does some go directly into changing the state of transistors and such? In other words, what makes electronic devices less than perfectly efficient?
This has probably been asked before, but I can’t find a thread on the topic.
A computer outputs information, and information carries no energy. A computer doesn’t do any “work” in the sense of force x distance. So in a sense, all computers have zero efficiency. That is, all the consumed power is converted into waste heat. (Except a tiny amount radiated as EM, but that’s not the intended product of the device so that’s also waste energy.)
Well the light from the monitor is how a person can see the information. I’d hardly call that a waste. The sound from the speakers serves a purpose, so it’s not really wasteful. By efficiency, I mean the energy that goes directly into the intended purpose of the device, such as the display of information, compared to that which is merely a necessary consequence to the design and is undesirable.
Energy goes into a computer as electricity. The computer performs work in these sense of turning motors for the hard drives and fans, running calculations (you’re moving electrons around) and powering the various components. It produces waste energy in the form of heat, non visible EM radiation.
Well yes, the monitor’s purpose is to emit light, so it’s possible to talk about its energy efficiency. But the actual heart of the computer (processor, memory, storage) doesn’t do any work or emit energy in any useful form.
No, but by information theory it must use energy. Here’s a link. Transmitting information on a channel (and information is transmitted inside a processor) does use information.
There is some EM radiation transmitted from a computer, and when you design one you have to shield it to meet the various laws about this. But the big killer is heat. Processors always generate excess heat, and it turns out that processes that allow you to run faster generate even more of it - and suck down more current. Fifteen years ago leakage current for CMOS circuits was near zero when the clock was off - now it is gigantic. Processors come with immense heat sinks to transfer away this heat, and the next generation is even worse. Cooling and electricity costs for server farms are very major, and one of the big reasons for the multiple core CPUs you see today are that you can get more work done without cranking up the clock further. Sun’s Niagara processor is marketed as being a lot more power efficient.
Anyone who has actually tried to work with a laptop on his or her actual lap should know this already.
Except for the tiny fraction of EM energy that gets radiated directly into space. Energy like the city lights that make such beutiful photos of the US from space, or the radio signal the furtherst of which are now, what? a hundred light-years out.
It has to do work. It’s exerting some effect on the electrons that enter the processor, electrons have mass (9.109 3826(16) × 10–31 kg), F=ma and W=FxD, erfo work is being performed.
Processor give off a great deal of waste heat as well.
Exactly, and I wanted to know what forms the unuseful energy take. If you plug just the computer in without the monitor, drives, or anything like that, it’s still going to pull a lot of power. That ends up as heat and electromagnetic radiation. Anything else?
Then it’s virtually all heat. There are rules in effect as to the amount of EM enerty electronic equipment can radiate. All the EM that isn’t radiated out of the box is absorbed within it and shows up ultimately as heat.
The electronics can also produce sound. For example, the horizontal sweep circuit in a television set. Power supplies and DC-DC convertors are also common sources of sound energy.
Just in the unlikely case you were wondering about this aspect, there’s a sense in which the electricity that isn’t used by your equipment and is not lost to radiation/heat and entropy goes right back out your wall socket back into the grid to complete the circuit.
As others like Voyager have pointed out, information is as real and measureable as matter and energy. Information cannot exist without hard physical reality in every single instance. Furthermore, the act of “creating” information itself must always produce useless heat and increase the universe’s entropy.
