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

Homework Help: What is the power - the rate at which it supplies electrical energy?

  1. Feb 14, 2009 #1
    1. The problem statement, all variables and given/known data
    A solar cell provides an emf of 0.70 V.
    If the cell supplies a constant current of 20.5 mA for 8.0 h, how much electrical energy does it supply? 413.3 J
    What is the power - the rate at which it supplies electrical energy?

    2. Relevant equations

    units J/s
    i keep getting .014

    3. The attempt at a solution
  2. jcsd
  3. Feb 14, 2009 #2
    Re: power

    Indeed. Is the 413.3 correct? I'll run a calculation n see what I come up with.
  4. Feb 14, 2009 #3


    User Avatar
    Homework Helper

    Re: power

    Use P = IV to find the power (current in Amperes x potential in Volts).
    Electric potential is sometimes called "electromotive force" or "voltage".

    Energy is Pt (power x time).
    These concepts are often confused with each other. Power is the rate at which energy is provided (or work is done). It is measured in units of Joules per second (also called watts).

    Don't forget to convert your mA into A, hours into seconds before using them!
  5. Feb 14, 2009 #4
    Re: power

    That's what I get too, 0.0144 W. The energy (413.3 J) per time (8hrs = 8*60*60 secs).
  6. Feb 14, 2009 #5
    Re: power

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook