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

Power distribution and heaters.

  1. Jan 13, 2012 #1
    This has to do with a fundamental doubt I have always had about power distribution. Say you hook up a room heater to your power supply. How exactly does the power distribution detect an increased 'load' and accordingly allot more power to your room. The way I understand it, the generating substation sends you electrical power at a fixed voltage (say 220V ). So 'loading' the power supply with the high resistance coil of a room heater should cause a reduced current to flow (according to V = IR ), and accordingly, a much smaller power output (according to P = i(squared)R ). So heaters should be the least power intensive of all household appliances, but obviously they are not, so what am I missing?
     
  2. jcsd
  3. Jan 13, 2012 #2
    a) The resisance of a room heater is neither high nor low, it is if fact just right to produce the desired power output according to P=IV=I2R=V2/R.

    b) You connect the heater in parallel with all the other loads you have. So the current through the heater is in addition to whatever current is flowing through other appliances you have. When you connect things in parallel, their combined resistance is calculated as 1/R= 1/Ra+1/Rb, that is you add conductances (reciprocals of resistance). See http://en.wikipedia.org/wiki/Series_and_parallel_circuits Note that R is always less than either Ra or Rb. So when you plug the heater in, total resistance as seen by the power supply decreases and the total current increases. If you go through the math you'll see it increases by just the right amount to produce the right amount of power in the heater.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook