2.  Think very carefully about commonly used electrical devices in your home such as a light bulb  What type of energy conversions are taking place?

3.  Inputted:  electrical energy  Outputted:  Light  Heat

4.  If you think about the purpose of a light bulb, it is designed to produce light in order to illuminate a room  Is the heat energy being generated as well of any use to us?

5.  Recently, the Ontario government has been pushing homeowners to change their old incandescent bulbs to the new compact flourescent bulbs (CFB)

6.  And incandescent light bulb and a flourescent light bulb both produce the same amount of light – which means that the USEFUL ENERGY OUTPUT generated by the bulbs is about the same  However, an incandesncent light bulb (IB) has a power rating of 60 W, whereas a CFB has a power rating of 15 W

7.  For about ¼ of the electrical energy input, a CFB produces the same amount of light as a IB  Which means that it is 4 times more efficient  This suggests that compared to the CFB, the IB wastes about 75% of its energy – it gets converted to heat energy  You should realize this since no one wants to touch an IB that has been on for an extended period of time

8.  CFB’s are more efficient when left on – they produce less heat energy which is not useful in the regular functioning of a light bulb  Since they also last longer – CFB’s are a good choice for replacing IB’s since they use less energy and they don’t have to be replaced as often

9.  A machine is a device that converts energy or force into a form that can be used to complete a job that the machine is designed for  A light bulb turns electrical energy into light energy  But what about other machines?  Are they as efficient?

10.  Your stove takes electrical energy and converts it to similar forms  But what type of energy, when discussing a stove, is useful?

11.  Remember that the type of device will determine what is considered to be USEFUL ENERGY OUTPUT  In a stove, heat is the USEFUL ENERGY OUTPUT whereas the light produced would be wasted energy  Whereas in a light bulb, this is opposite

12.  There are many interactions going on in any machine at the molecular or subatomic level that we can’t see  Remember that most machines create movement: in a stove or a bulb, electrons are forced to move through resistors  These small particles carry the inputted energy and in order to convert it to another type, it has to undergo some interaction that saps energy from it

13.  Electrons slam into the molecules of resistors, increasing the motion of these particles and thus creating energy in the form of heat  In mechanical devices like cars, moving metal parts rub up against each other creating heat through friction

14.  That most cars are less than 50% efficient?  Most of the gasoline you pump into a car (chemical energy) is converted to mechanical energy through combustion  This creates motion in metal parts such as pistons inside an engine  This generates a great deal of heat – think about how hot the hood of your car gets after a long drive  http://www.grc.nasa.gov/WWW/K- 12/airplane/engopt.html http://www.grc.nasa.gov/WWW/K- 12/airplane/engopt.html

15.  The amount of energy put into the machine to complete a job is the useful energy input  For example, for both the light bulb and stove, this is the amount of electrical energy inputted as defined by E = Vit  It is important to note that for all machines, useful energy input is always GREATER than useful energy output

16.  Since there is no such thing as 100% efficient machine, the following must be true:  Useful energy input > Useful energy output  Why is it impossible to have a machine that has an efficiency?

17.  Efficiency values of over 100% violate the Law of Conservation of energy  It essentially means that the work being completed by the machine is being completed for free – since you are getting more out of the machine than you are putting in

18.  UEI = useful energy input in J  UEO = useful energy output in J  Efficiency = UEO x 100% UEI Where: UEI > UEO for a real machine