1. We’ll look at the difference between a cell and a battery.

2. When most of us see a device like this, we call it a battery. + – A Battery

3. Technically, it’s not really (click) called a battery, it’s called a chemical cell + – A Chemical Cell A Battery

4. A battery is actually defined as a combination of two of more chemical cells connected to each other. A battery is a combination of two of more chemical cells connected to each other.

5. For example, if we attach the positive end of one cell to the negative end of another (click) like this… + – a cell + – A battery is a combination of two of more chemical cells connected to each other.

6. It forms a battery of 2 cells in series. + – a cell + – A battery of 2 cells in series. A battery is a combination of two of more chemical cells connected to each other.

7. + – A battery of 2 cells in series. Adding another cell like (click) this will give us a battery of 3 cells in series A battery is a combination of two of more chemical cells connected to each other. + – + – A battery of 3 cells in series.

8. The voltage of a cell is measure of how much potential energy electrons gain as they go through a cell V + –

9. Many common cells have a voltage of 1.5 volts. V = 1.5 V + –

10. When cells are connected in series, or positive to negative, When cells are connected in series, each cell adds potential energy to the electrons going through it, so their voltages add up.

11. each cell adds potential energy to the electrons going through it, When cells are connected in series, each cell adds potential energy to the electrons going through it, so their voltages add up.

12. So their voltages add up. When cells are connected in series, each cell adds potential energy to the electrons going through it, so their voltages add up.

13. So if a single cell has a voltage of 1.5 volts. V = 1.5 V + –

14. Two cells in series will have a total voltage of 3 volts. + – + – V = 3.0 V Two cells in series will have a voltage of 3.0 volts

15. To understand how this works, we imagine one electron going through one cell + – + – V = 3.0 V e–e– 1.5 V

16. As it goes through, it picks up 1.5 volts of potential energy and goes into the other cell, + – + – V = 3.0 V e–e– 1.5 V

17. Where the same electron picks up another 1.5 volts of potential energy + – + – V = 3.0 V e–e– 1.5 V

18. So this single electron has picked up 1.5 volts of potential energy from both of the cells + – + – V = 3.0 V e–e– 1.5 V The electron has picked up 1.5 volts of potential energy from both cells.

19. So it has picked up a total of 1.5 plus 1.5, which is 3 volts of potential energy + – + – V = 3.0 V e–e– 1.5 V The electron has picked up 1.5 volts of potential energy from both cells. So it has picked up a total of 3.0 volts of potential energy. 3.0 V

20. Therefore, the voltage on the voltmeter is 3 volts. + – + – V = 3.0 V e–e–

21. Three 1.5 volt cells in series will have a total voltage of 1.5 V = 4.5 V + – + – + – 1.5 V Three cells in series will have a voltage of 1.5 V + 1.5 V + 1.5 V = 3 × 1.5 V = 4.5 V

22. + 1.5 V = 4.5 V + – + – + – 1.5 V Three cells in series will have a voltage of 1.5 V + 1.5 V + 1.5 V = 3 × 1.5 V = 4.5 V

23. + 1.5 V = 4.5 V + – + – + – 1.5 V Three cells in series will have a voltage of 1.5 V + 1.5 V + 1.5 V = 3 × 1.5 V = 4.5 V

24. or 3 times 1.5, which is (click) equal to 4.5 volts V = 4.5 V + – + – + – 1.5 V Three cells in series will have a voltage of 1.5 V + 1.5 V + 1.5 V = 3 × 1.5 V = 4.5 V

25. Now we’ll look at a different arrangement. (click) When two cells are brought together + – + – When two cells are brought together,

26. so that their positive ends align, (click) and their negative ends align. + – + – When two cells are brought together, so that their positive ends align and their negative ends align

27. And the two positive ends are connected by a conductor, + – + – When two cells are brought together, so that their positive ends align and their negative ends align and these are connected to a conductor,

28. and the two negative ends are connected by a conductor, + – + – When two cells are brought together, so that their positive ends align and their negative ends align and these are connected to a conductor,

29. They form a battery of two cells in parallel + – + – When two cells are brought together, so that their positive ends align and their negative ends align and these are connected to a conductor, they form a battery of cells in parallel.

30. In parallel, voltages do NOT add up. + – + – When two cells are brought together, so that their positive ends align and their negative ends align and these are connected to a conductor, they form a battery of cells in parallel. In parallel, voltages do NOT add up. V

31. For example, if the voltage of one cell is 1.5 volts, + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V

32. + – And we add another cell in parallel, + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V

33. + – the voltage will still be 1.5 volts + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V

34. + – + – even adding a third cell in parallel + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V

35. + – + – will still give us a voltage of 1.5 volts + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V

36. + – To understand why this happens, we consider two cells in parallel and two electrons by the voltmeter. One of the electrons (click) goes through one cell + – In parallel, voltages do NOT add up. V = 1.5 V e–e– e–e– 1.5 V

37. + – and picks up 1.5 volts of potential energy. + – In parallel, voltages do NOT add up. V = 1.5 V e–e– 1.5 V e–e–

38. + – and the other electron (click) goes through the other cell + – In parallel, voltages do NOT add up. V = 1.5 V e–e– 1.5 V e–e–

39. + – and picks up 1.5 volts of potential energy. + – In parallel, voltages do NOT add up. V = 1.5 V 1.5 V e–e– e–e–

40. + – So each electron has picked up potential energy from only one of the cells. Neither of the electrons go though both of the cells. + – In parallel, voltages do NOT add up. V = 1.5 V Each electron has picked up potential energy from only one cell. 1.5 V e–e– e–e–

41. + – Voltage is a measure of potential energy per electron. + – In parallel, voltages do NOT add up. V = 1.5 V Each electron has picked up potential energy from only one cell. Voltage is a measure of potential energy per electron 1.5 V e–e– e–e–

42. + – Each electron has picked up only 1.5 volts, (click) so the voltage is still 1.5 volts. + – In parallel, voltages do NOT add up. V = 1.5 V Each electron has picked up potential energy from only one cell. Voltage is a measure of potential energy per electron 1.5 V e–e– e–e–

43. To review, a single unit like this is called a chemical cell, rather than a battery + – A Chemical Cell

44. + – When cells are connected with positive to negative, they form a battery of cells in series. + – + – A battery of three cells in series 1.5 V

45. + – When cells are connected in series, their voltages add up. + – + – When cells are in series, their voltages add up. 1.5 V

46. + – So, for example, the total voltage of three 1.5 volts cells in series + – + – When cells are in series, their voltages add up. 1.5 V Total Voltage = 3 × 1.5 = 4.5 V

47. + – Is equal to 1.5 + 1.5 + 1.5 + – + – When cells are in series, their voltages add up. 1.5 V Total Voltage = 1.5 + 1.5 + 1.5

48. + – Which is 4.5 volts. + – + – When cells are in series, their voltages add up. 1.5 V Total Voltage = 1.5 + 1.5 + 1.5 = 4.5 V

49. + – + – When cells are arranged so all their positive terminals are connected to a conductor and all their negative terminals are connected to another conductor, they form a battery of cells in parallel. + – A battery of 3 cells in parallel 1.5 V

50. + – + – And when cells of equal voltage are arranged in parallel, the total voltage of the battery is the same as the voltage of a single cell. + – A battery of 3 cells in parallel 1.5 V V = 1.5 V