Unit 4 Electricity and magnetism


Notes
  • Since power is related to voltage and current (P=IV) and energy is related to power and time, E=Pt can be rewritten as:

    E=IVt

    E=energy (J)

    I=current (A)

    V=voltage (V)

    t=time (s)

    We simply substitute IV for P to get the formula above.

  • Example
    Calculate the energy transferred by a 12V hairdryer, running on a current of 0.50A, that is left on for 8.0 minutes.
    Step 1

    List all the information in symbol form and change into appropriate and consistent SI units if required.

    V=12V

    I=0.5A

    t = 8.0 minutes
    = 8 × 60
    = 480s

    E=?

    Step 2

    Use the correct formula.

    E=IVt

    Step 3

    Calculate the answer by putting the numbers into the formula.

    E = IVt
    = 0.5 × 12 × 480
    = 2880J

ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.

 
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