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

B Physics Equations for Electrical Power

  1. Jun 13, 2018 #1
    I'm in year 11, doing Physics for GCSE and my actual ending GCSE is on Friday which Is where I finish school.

    I'm 16 and in the UK, I need help with the following equations:
    P = I^2 x R (why is this equation used)
    - all the power equations
    - How to calculate uncertainty

    << Mentor Note -- OP has edited this post to correct the equation. See Russ' quote below for the original equation that Russ is replying about >>
    Last edited by a moderator: Jun 13, 2018
  2. jcsd
  3. Jun 13, 2018 #2


    User Avatar

    Staff: Mentor

    That equation isn't correct, but here's a discussion (now locked) of how you can combine Ohm's law and the electrical power equation in various ways for various purposes:
  4. Jun 13, 2018 #3
  5. Jun 13, 2018 #4


    User Avatar

    Staff: Mentor

    No prob - just have a look at the link, se if it gives you what you need snd let us know if you have any follow-ups.
  6. Jun 15, 2018 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I'm sitting in my car waiting for my twins to finish their GCSE physics exam so this is a bit late but....

    First think about _where_ the power is being dissipated.

    If we are talking about the power dissipated in a resistor then I and V refer to the current and voltage through and across the resistor.

    If you are talking about the power delivered by a battery then I and V apply to the battery.

    In some cases you only know one variable (I or V) so you can use..

    And ohm's law

    To make either...


    Then which you use depends on which variable you know.

    One of my son's has just called to say the exam was "ok but challenging". How did you find it?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?