Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is all electrical energy eventually lost as heat in solid state electronics?

  1. Jan 7, 2013 #1
    I've never heard it said before but it appears to me that all electrical current that flows in a solid state component system; processors, diodes, transistors, resistors, etc. is eventually dissipated as heat. What are your thoughts about this?
     
  2. jcsd
  3. Jan 7, 2013 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    All energy, including electrical, is eventually lost as heat. That's the "second law of thermodynamics".
     
  4. Jan 8, 2013 #3
    So it appears to me then, unlike other kinds of circuits where electrical energy is converted to mechanical energy or chemical energy, no actual work is done in most digital circuitry. It only results in heat. I guess that's why you need all those heat sinks and fans blowing on CPUs.
     
  5. Jan 8, 2013 #4

    Low-Q

    User Avatar
    Gold Member

    It is possible to recycle mechanical work, make work out of heat etc. However, efficiency in all things are not 100%. Eventually ALL electrical or mechanical energy will be lost as heat.

    Vidar
     
  6. Jan 8, 2013 #5

    phinds

    User Avatar
    Gold Member
    2016 Award

    Uh ... your computer doesn't have any lights on it? How about a disk drive? How about a screen?
     
  7. Jan 8, 2013 #6

    russ_watters

    User Avatar

    Staff: Mentor

    None of those devices do more than temporarily convert electrical energy to something other than heat for more than a few milliseconds, except for the small amount of kinetic energy stored in the spinning disk drive (which over time is inconsequential compared to the continuous loss due to friction).
     
  8. Jan 8, 2013 #7

    phinds

    User Avatar
    Gold Member
    2016 Award

    Agreed, it was just that he seemed to think ALL went to heat, period, and I wanted to point out that this is not exactly right. Actually, the screen is on all of the time and there's probably a modest amount of energy getting converted to light.
     
  9. Jan 8, 2013 #8
    Home computers do convert much of the electrical energy into mechanical energy (speakers) and light energy (monitor screens). Smart phones use most of their energy to light up the screen. Industrial computers operate robots and other machinery. Computers in cars drive fuel injectors, ignition coils, etc.

    The purpose of a computer is to increase the usefulness of energy. Text and graphics on a screen is more useful then a 60 Hz 120 volt sine wave. Properly timed spark and fuel delivery is more useful to an engine then raw 14 volt DC current. etc...

    Making energy more useful is done by making it more orderly, decreasing it's entropy. The 2nd law of thermodynamics tells us that the entropy of a system must always increase. If we want to design a system which decreases the entropy of some energy, it will be unavoidable that it will increase the entropy of some other energy. The highest entropy state that energy can take (under terrestrial conditions) is heat. Therefore the energy that comes into a computer is divided into 2 classes. Entropy is removed from the energy designated to become useful output and added to the energy which becomes un-useful output (heat).

    Edit: useful and un-useful may have been a poor choice of words. The heat generated by my computer in the winter is every bit as useful as the heat generated by my furnace. I hope my meaning was clear.
     
    Last edited: Jan 8, 2013
  10. Jan 8, 2013 #9

    russ_watters

    User Avatar

    Staff: Mentor

    Well almost all of the electrical energy does something useful before being converted to heat. Not just that which is turned into light or mechanical energy.
     
  11. Jan 8, 2013 #10
    Well, actually, I was generalizing and knew about those other devices. I was thinking of the logic circuitry on the circuit boards.
     
  12. Jan 9, 2013 #11
    Why do solid state devices need to produce heat?

    Their input is organized electric current - energy with very little entropy. The entropy that was included in the source of electricity, like heat engine, was rejected as the cooling heat of the heat engine - the shaft to electric generator and the wires from generator received energy free of entropy.

    So, can a solid state device operate just by rearranging the organized energy, and avoid creating heat?
     
  13. Jan 9, 2013 #12

    russ_watters

    User Avatar

    Staff: Mentor

    Every time it "re-arranges" the energy, it has to discard some.
     
  14. Jan 9, 2013 #13
    Also, heat is lost by the resistance in the circuits.
     
  15. Jan 10, 2013 #14
    But the screens are so inefficient that most of that energy comes out the screen as heat rather than light.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is all electrical energy eventually lost as heat in solid state electronics?
Loading...