There is a direction to the flow of electricity, just as for the flow of a fluid. You have to keep track of the direction of the electrical current in order to understand a circuit. Some devices will not work properly if the current is going the wrong way (this is also true of fluid devices -- consider a kitchen sink with the water lines and sewer lines interchanged!). This suggests that there is something moving in the wires when there is a current; we imagine an "electrical fluid" that emerges from the positive end of the battery. The electrical fluid is called charge; what is actually moving are electrons. There is a complication in the description, that the electrons have a negative charge, with the result that the direction of the current is the opposite of the direction of motion of the electrons. Don't think about the electrons! We can describe water flowing in pipes without talking about molecules; we don't need a "particle" description here, either. The experiments that are able to distinguish between the two descriptions (electrons moving one way or positive charges moving the other) are fairly subtle; there is no experiment we can do that will reveal which way things are going.

Let's review the electrical components from this point of view:

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• A D-cell battery has two ends. When the battery is powering a circuit, the current comes out of the positive end (the top of the battery -- the end with the bump on it) and goes to the negative end (the bottom).


• Many electrical components, like the motor in your kit, have wires that are different colors. The red one is to be connected to the positive end of the battery, and the other (whether blue or black or almost any other color) is to be connected to the negative end. If you connect it the wrong way, it may do the something different, or even not work at all. Or it may work just as well either way. We can understand this aspect of electrical devices when we realize that there is a flow in the wires, and that it has to go in the right direction. The current comes out of the positive (bumpy) end of the battery, travels on the red wire into the device, and comes out on the black wire on its way to the negative end of the battery.

Time to explore! Here are some things to think about and do.
Do these explorations. Record in your journal about what you learned, and any questions or problems you encountered.  We will ask to see your journals at the end of the workshop. 

• The two ends of a battery are different, and the two connecting points of a light bulb are different, too. Then there are four ways to make a light bulb light using a battery and one wire -- by touching either part of the light bulb to either end of the battery, and then completing the circuit with the wire. Verify that the light bulb works all four ways. Make sketches of the four arrangements.
  Since the light bulb doesn't care which end you use, the diagram symbol for the light bulb doesn't distinguish between the ends. If you represent the four arrangements as circuit diagrams, how many different diagrams do you get?

  

• Attach a piece of tape to the shaft of the motor, to make a little flag. Now study the effect of current direction on the motor. Is there a reason for having wires of different colors on the motor?

  Yes    No

  
  

Check the box when you are done: