Energy calculation example 1

This page is under construction!!!

Intro

Calculations are important. Numbers are not always what they seem to be. The amounts of energy can be very small or very big. This is not related to the effort which is required to use a method or develop a strategy. Consequences are also important, for example for the environment. Investments required for starting also have to be considered.

Example 1

Batteries Energy indication: eg 1200 mAh means for one hour (3600 seconds) 1200 mA = 1.2A To know the energy you have to multiply by the Voltage, say this is a 9V battery: P = 9 * 1.2 Joule/second, total energy is E = 9 * 1.2 * 3600 = 38880 J

(You have to calculate in standard units, like A=Ampere, V=Volt, C=Coulomb, then you get J=Joule.)

So the same battery, but running at 1.4V has a total energy of: E = 1.4 * 1.2 * 3600 = 6048 J. Now...these are the calculations, but reality is chemistry inside a battery, so depending on what is inside and the quality, the battery might be able to deliver this energy or less.

Example 2

If you know the energy in Joule, you can compare:

eg eating a banana means your body gains (on the average banana) 202 kJ.

eg charging my cellphone is 4 hours at 5V with a current of 700 mA, calculating: Energy = 4*3600*5*.7 = 50400 J = 50kJ so with the energy out of a banana I could charge my cell phone 4 times...at the same time delivering the same energy using a dynamo and my muscles for 4 hours (hand crank USB device) is not really comfortable for a human being!

eg a human being of 60 kg running up a flight of stairs, 3 meter high is 1900 J = 2kJ [1] Can you keep running up flights of stairs during 25 * 3.5 seconds = 90 seconds for charging your cell phone? Yes you can, but the dynamo would have an efficiency of 50%, this becomes 180 seconds, 3 minutes...which is still perfectly possible, but slowly you'll get a bit tired of charging your cell phone this way?