Electrical Power

by Mark Landmine, Joey Trachea, and Tyler Meatloaf 

Table of Contents

Here's the quantities you can know: These quantities are defined and explained on other pages, except for electric power.

New Quantities

And here are the formulas that we have so far:
  1. V = IR

Defining Electric Power

Electric power is the convesion of electric energy into light or thermal energy.  In a lightbulb, if the current is large enough the kenitic energy of the electrons will be transfered to the atom that it collides with.  This causes an increase in temperature of the atoms of the wire, and eventually the emission of light.

Power defined is the rate at which energy is transformed.

So we have two new formulas:


Since we have previously found that Q/t is current, (I) the formula can be simplifed into P=IV.  Using Ohm's Law,(V=IR) this formula can be written in two other ways:




So now we have all the formulas we need for solving electric power problems:


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General Problem Solving Strategy:

  1. Read the problem.
  2. Go through the problem and figure out what is given or implied

  3. Make a list, and identify the quantities you know.
  4. Find any formula that will allow you to calculate

  5. anything that you don't know, and apply it.
  6. Add what you just found in the last step to your list of knowns.
  7. Check to see if you have found the answer. If not, repeat the

  8. previous two steps until you are done.
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Example problem 1

Calculate the resistance of a 1000 Watt microwave designed for 27 Volts.

Here is what you start with

So, if you look at the formulas, P=(V^2)/R seems most logical.

putting in numbers:

R=(V^2)/P=27^2/1000=.729 Ohms

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Example problem 2

A pool heater running on 150V, and draws a current of 30A.  How much energy does it use per week if it is used for 9 hours a day.

Here's what we know: