3.2 Conservation

Efficiency

Light Bulbs

Test your knowledge by trying the problems below.  

Here's some practice for your new equation:

E f f i c i e n c y space equals space fraction numerator U s e f u l space E n e r g y space O u t over denominator E n e r g y space I n end fraction space x space 100 percent sign

Example #1:
An "old style" (incandescent) light bulb converts energy as shown in the Sankey diagram below:

light 1
a)  For every 100J of energy that the light uses, how much is converted into light energy?
b)  For every 100J of energy that the light uses, how much is converted into heat energy?
c)  We'd consider the "useful energy" to be what?
d)  We'd consider the "wasted energy" to be what?
e)  Calculate the efficiency of the light.
f)   If you were going to use this light bulb to heat a small area, we'd have to redefine what was "useful energy."   What would be the efficiency of the light in this case? 




Try before checking solution.

Solution



Example #2:
An "new style" (LED) light bulb converts energy as shown below:

light 2
a)  For every 100J of energy that the light uses, how much is converted into light energy?
b)  For every 100J of energy that the light uses, how much is converted into heat energy?
c)  We'd consider the "useful energy" to be what?
d)  We'd consider the "wasted energy" to be what?
e)  Calculate the efficiency of the light.
f)   If you were going to use this light bulb to heat a small area, what would be the efficiency of the light? 




Try before checking solution.

Solution



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