Current  Number of coulombs per second (by the way, do you see now why a coulomb was defined to be such a ‘large’ amount of charge?) Voltage  Number of joules per coulomb (i.e. the energy carried by each coulomb of electrons)

1 J e e e e e We’ve got all this energy! Let’s go and give it to a bulb, or a motor, or something! The Coulomb Gang 1 V 1 J e e e e e This battery gives us twice as much! 2 V

Cells – Fixed Voltage  A cell is a fixed-voltage device. It has its voltage written on it.  The cell will always give the same number of joules to each coulomb coming through. A 5 V battery will always give 5 J to every coulomb of electrons.  Somehow it is always able to keep up. Even if the coulombs are coming through thick and fast (high current), it will still manage to give 5 J to every coulomb passing through.

electrons all start moving at once when switch is closed

 We always refer to the voltage across a component (not through it).  The voltmeter tells you the difference between the joules per coulomb going into the component and the joules per coulomb coming out.

Conservation of Energy  All the joules given by the battery to the electrons are exactly used up by the time the electrons get back to the battery.  Question: You’ve already seen that you can get different currents with the same battery, depending on what you connect to it. What difference will the size of the current make to the lifetime of the battery?

1 J e e e e e The Coulomb Gang – all out of energy 2 V e e e e e V This battery is giving 2 J to every coulomb of electrons passing through. The voltage is (+)2 V.

1 J e e e e e e e e e e V This bulb is taking 1 J from every coulomb of electrons passing through. The voltage is (-)1 V.