How much works could be obtained from a twelve volt battery as a one half Coulomb charge is moved from the positive terminal to the negative terminal of the battery?

Answer 1

When work is mentioned in connection with electrical devices, we are quick to think of measures of energy such as joules, and measures of power such as watts. Here the usual terms needed to figure out the power easily, such as volts and amps or volts and path resistance, or current and path resistance are absent. Instead we have volts and also coulombs which effectively constitute a number of electrons passing from one terminal to the other of the battery. This is equivalent to considering a current flowing for a particular time. The relation is that charge is given by current times time. So a half Coulomb is the same as a half ampere-second. Given these more familiar terms, volts, amps, seconds, it looks rather easier to work the result, because the normal energy unit, the Joule, is equal to the current in amps times the voltage in volts times the time in seconds. So V x I x t = 12 x 0.5 = 6 joules. This can also be expressed as 6 watt.seconds This is the energy available to do work, in fact.