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Batteries and Bulbs Introduction The following activities will give you the chance to experimentally explore the behavior of circuits made from batteries and bulbs. Circuits are an extremely important concept in Physics 142. This lesson has been designed to help you begin to develop an understanding of some fundamental circuit concepts. This lesson has not been designed to have you verify some facts given in lecture or in your text, instead you are to explore, make observations, and draw your own conclusions based solely on your observations. The (thought balloon) symbol is used to denote a ponder question (or prediction question). This question must be answered before you try a particular experiment. These questions are designed to have you think about what you expect to happen in a particular experiment. These ponder questions will be graded for completeness, but they will never be graded as "right" or "wrong." Activity #1 is to be completed individually. That is, each person should work through Activity #1 on his or her own. Activity #1

Battery

#49 Light Bulb

Wire

1. Suppose you were given a single standard battery (just like the batteries in a flashlight), a single light bulb, and a single wire. Could you make the bulb light? If you predict you can’t light the bulb, explain why not. If you predict you can, draw a picture clearly showing how you would make the bulb light, and explain why you think it would work.

Once you have completed your explanation, you should show your instructor that you have finished your prediction and then he/she will give you some equipment to test your prediction. Try several different arrangements with just the single wire, battery, and bulb. 2. Was your prediction correct? How many different ways can you find to make the bulb

light with just these three pieces? In your logbook, record precisely what you do to make the bulb light (picture(s) may be helpful).

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• It is extremely important that you not continue until you have successfully made a light bulb light. If by chance your bulb is burned out, then request a new one from your instructor.

3. Based just on this activity, what conditions seem necessary for the bulb to light? Once you have completed activity #1, then you can join forces with your lab partner(s) to complete the rest of the lesson.

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Activity Guide © 2010 The Humanized Physics Project Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780 Page 2 of 5

Activity #2 Obtain various materials from your lab instructor (such as a coin, lead, wood, and aluminum foil). One at a time, insert these materials into your working circuit. What happens? Does the light bulb still light? Try this experiment and record the results for at least six different materials (copper, lead, your finger, your shirt,....). 4. How do these different materials change the conditions that allow the bulb to light?

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• Please return the battery, bulb, and wire neatly to the box in the front of the class before you go to the next activity.

Activity #3 - Why Does the "Chirping Chick" Toy Chirp? Each group should obtain a Chirping Chick toy (if there are not enough toys, you may have to combine groups for this activity). Using this toy, have your group try out the following mini-experiments. Record the result of each experiment in your logbook. Mini-experiments: A. Place the chick in the palm of your hand. B. Using two fingers of your right hand, place them touching

each of the toy's feet. C. Place the chick on the back of your hand. D. Place the chick on your upper arm. E. Place the chick on the tabletop. F. Place the chick on a piece of aluminum foil. G. Using one finger of your right hand and one of your left

hand, place them touching each of the toy's feet. H. Try any other experiment of interest… Using your results of these experiments, answer the following questions. 5. Consider the chirping chick toy. Based only on the evidence of your experiments, is the

battery in the toy or in your body? Explain your experimental evidence. 6. What conditions need to be met in order for the chick to chirp? How is this similar to or

different from the battery, bulb, and wire system? 7. What is it about the human body that lets the chick chirp sometimes but not other times?

Try to explain in detail. Why do you think parents tell their young children not to put their fingers in power outlets?

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Activity #4 You may have had some difficulty holding all of the equipment together to make the bulb light in Activity #1. This can be made easier with some additional pieces of equipment. At the front of the class you should find the supplies needed for Activity #4. Equipment: Battery(ies) in a holder, Two identical #13 light bulbs in sockets, Several wire

connectors, One key switch Get a battery that has been placed in a holder and a bulb that is screwed into a socket. Now the wires can be connected easily. Go ahead and make this bulb light. This arrangement is called a circuit. If the circuit is left connected for too long, the battery will weaken and it will have to be replaced. To avoid this, place a key switch in the circuit such that the bulb only lights when the switch is closed. Imagine you are trying to explain to someone how to connect the circuit as you have just done. This is much easier to do with pictures than with words. To make the pictures easier to draw and understand, standard symbols are used to represent the various elements of the circuit. These symbols are identified below.

battery

wire (or any connection)

switch The symbol for light bulbs is not standard, but some typical symbols include:

Or

When a picture of a circuit is drawn with these symbols, it is called a circuit diagram. A diagram for the circuit you constructed at the start of Activity #4 with the switch would appear as this: 8. Draw a circuit diagram that represents the chirping chick in mini-experiment G.

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Activity #5 It is helpful at this point to construct a mental model of what is happening with the circuit. In Activity #1, you might have decided that something flows from the battery to the bulb, giving the bulb some energy. We call this flow of charge electrical current.

9. Discuss with your partners which of the following you think is true about the electrical current at various points (A, B, C, D) in the circuit drawn below. Explain why you think your choice is true.

A B

CD

• The electrical current is largest at A. • The electrical current is largest at B. • The electrical current is largest at C. • The electrical current is largest at D. • The electrical current is the same everywhere. • The current is the same in AB and smaller than in CD. • The current is the same in AB and larger than in CD.

Now you will determine which answer might be best with the following experiment.

Add a second bulb to your circuit as shown. This is called connecting the bulbs in series.

Two Identical Bulbs in Series

10. (a) When you close the switch, do both bulbs glow? How does the brightness of one bulb

compare to the other? (b) Which answer from above (#9) supports these observations? Why do you think so? Discuss with your partners and predict what would happen if one bulb is unscrewed from the socket. Explain your reasoning for your prediction. 11. Conduct an experiment to try it and see what happens. Record your results. Was your

prediction correct? Try to explain what you observe.

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Activity #6 Suppose you were to connect the two identical bulbs as shown to the right. This is called connecting the bulbs in parallel.

Two Identical Bulbs in Parallel

Discuss and predict the following: How would their relative brightness compare? How would the brightness of each bulb compare to that of a circuit with a single bulb? Explain your reasoning. 12. Connect two bulbs as shown and test your predictions. Record your observations and any

conclusions you can draw about bulbs in parallel. Discuss and predict what would happen if one bulb is unscrewed from the socket and explain why you think this. 13. Try it and see what happens. Explain what you observe. Activity #7 Obtain a #40 and a #46 bulb from your lab instructor and build the following series circuit. 14. Which bulb seems to cause the greater obstacle to the

flow of current in the circuit? Explain your evidence. Hint: Think about how the brightness may be related

to or caused by the presence of an obstacle.

# 40

# 46

Two Non-identical Bulbs in Series

15. Rewire the circuit so that the #40 and #46 bulbs are in parallel. Observe which of the two

bulbs is brighter. (a) How does this result compare to the result when the two bulbs were in series? Is the

same bulb the brightest? (b) Attempt to explain the results for these two different circuits (parallel and series) for

these two bulbs. Hint: An individual bulb (say the #46 one) will glow more brightly when more current is

flowing through it. End of Lab Cleanup

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• Return the #40 and #46 bulbs to the containers on the lab instructor’s desk. • Place the two identical #13 bulbs back into the sockets. • Return all equipment including the chick toys to the front equipment table.