Is it watt per second or watt per hour

  1. Say I have a device (Thermoelectric generator) that "generates power" at 4 watts, as per watt meter reading, is it producing 4 watts a second or 4 watts an hour. I say it is producing 4 watts a second but my brother in law says 4 watts an hour so the watt meter can tell the future. Please bear in mind I am not consuming energy but generating energy.
  2. jcsd
  3. Hello .Watts is a unit of power(Joules per second) so the 4 Watt device is producing 4 Joules per second.

    To clarify this further the Joule is a unit of energy so the device is producing 4 Joules of energy every second.
    Last edited: Jul 6, 2011
  4. Watts are a unit of power, so it doesn't make sense to talk about watts per hour (or per second). They already have the "per unit time" built in.
  5. It is generating 4 Watts for as long as you leave it on. :rolleyes:

    See Dadface's answer above. Power is a measure of how fast you generate energy (or consume it). Joules is a measure of total generated energy.

    Your brother may be getting confused by the units WHr which is also a measure of energy (that's Watt hours, not Watts per hour). If you leave a 4 W device running for one hour, you generate 4 WHr of energy, which is 4 JHr/s x 3600 sec / 1 Hr, which is 14400 Joules.
  6. I thank you all very much for the explanation
  7. Pythagorean

    Pythagorean 4,483
    Gold Member

    Watts per time is the change in power over time :)
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