science history

A coulomb of charge is defined in terms of the energy released when the charge falls through a potential dfference of 1 volt. Under this definition, the energy released is only 1 Joule.

In fact, 1 Joule of energy is quite a small amount of energy. It can only raise the temperature of 1 gram of water by about 0.2 degree Celsius.

2010-01-14 16:09:45 補充：
Moreover, a 800 mAh AAA battery that we used in daily life has already had a capacity of 2880 coulombs of charge. A 1 kW heater operated under 220v domestic voltage for 10 minutes will consume 2700 coulombs of charge. Hence, a coulomb cannot be regarded as a "large unit ".

2010-01-14 16:12:47 補充：
It is only in the microscopic world in which charges in particles like protons and electrons are concerned that the "coulomb" appears as "large". But be aware that when the unit "coulomb" was defined, protons and electrons were still unknown to human.