# Teacher Investigations

A partial listing of the teacher investigations is contained here.

## Investigation E1: Batteries and Bulbs

### Activity E1.1: What conditions do you think enable the bulb to light?

(Seat Activity/Discussion)

Goals: Observe the behavior of batteries and bulbs when connected. Begin developing ideas about how electricity works.

Equipment: 1 battery (D-cell), 1 piece of wire with both metal ends exposed, and 1 bulb (oblong #47).

1. WHAT'S YOUR IDEA? What arrangements of battery, bulb, and wire do you think will enable the bulb to light? Imagine that you have a single battery, a single bulb, and a single piece of wire. In the space below make a diagram of these three objects arranged so that the bulb will light. Describe in words what you are trying to represent in the diagram and say why you think this arrangement will work-in other words, why do you think the arrangement will light the bulb? Use pictures of the battery and bulb as shown above and use a line to represent the wire as you draw your diagram.

2. WHAT ARE THE GROUP'S IDEAS? Listen and look as the members of the group describe arrangements that they think will light the bulb. Pay careful attention to why they think their arrangements will light the bulb. For each one that is different from yours, record the diagram and the reasons for that diagram. Try to come up with as many distinctly different arrangements as possible that will light the bulb. Continue on to the back of this page if you need the space.

3. MAKING OBSERVATIONS: When the group is pretty sure of their ideas, try each configuration. Record whether the bulb lights for each arrangement. If none of the arrangements designed by the group result in the bulb lighting, then try some new ones. Make a diagram of each new arrangement that you try. Use the back of this sheet if necessary.

4. MAKING SENSE: Compare your observations with your predictions. Did any of the configurations that someone in your group thought would light the bulb, not work? If so, with your group, make a list of reasons that were used to support those configurations which are now questionable. Put your list in the space below.

Drawing A Conclusion: What conditions enable the bulb to light?

5. WHAT'S YOUR IDEA? On the basis of your observations of arrangements which work and those which do not, try to decide on conditions that must be met to light the bulb and list these conditions below. Include reasons and refer to arrangements the group has tried for evidence in support of your conclusions.

6. WHAT ARE THE GROUP'S IDEAS? Discuss with your group and try to reach some consensus on the conditions that must be met to light the bulb. List any new or changed conditions below. Consider things that you have observed so far in this investigation as you discuss this question.

Conditions for the bulb to light (group consensus):

DEFINITION: Electrical Circuit: An arrangement of electrical elements that meets the same kind of conditions as those necessary to light a bulb is called an electrical circuit. The items in a circuit, which make up the circuit, are called circuit elements.

## Investigation E2: "Obstacleness and Oomph"

### Activity E2.2: Wires of Different Materials and How They Affect Bulb Brightness

(Laboratory Activity)

Focusing Question:
If we used wire that presents more obstacle to the flow of charge, what do you expect would happen to the brightness of the bulb as we include more and more of this wire in the circuit?

Equipment: 4 batteries, 1 4-battery holder, 1 bulb (oblong #47), 1 bulb socket, 1 tap switch, 1 compass, 1 length of high "obstacleness" wire, and wires (12-pack of wires with clips).

At this point consider, but DO NOT ASSEMBLE, the following circuit.

1. WHAT'S YOUR IDEA? If we used wire that presents more obstacle to the flow of charge, what do you expect would happen to the brightness of the bulb as we include more and more of this wire in the circuit? In the space below describe why that answer makes sense to you.

2. WHAT ARE THE GROUP'S IDEAS? Listen as the members of the group describe their ideas. Pay careful attention to the reasons behind their explanations. Try to come to some consensus. Describe the group's conclusions below. Include reasons why this consensus seems reasonable. If you cannot come to a consensus, then make a list of the possibilities and the reasons why each possibility seems reasonable. Use the back of the previous page if necessary.

3. MAKING OBSERVATIONS: When the members of the group are pretty sure of their ideas, assemble the new circuit. Your instructor will show you how to use the high "obstacleness" wire. Observe and record the brightness of the bulb as you vary the length of high "obstacleness" wire in the circuit. Record your observations.

List any discrepancies between your predictions and observations.

4. MAKING SENSE: Consider any discrepancies that you notice between your predictions and your observations and discuss them with your group. Record the group's conclusions in the space below.

General Rule #1: The greater the "obstacleness" in a circuit, the (fill in the blank) the flow of electricity.

What should we be assuming remains the same in this case?

(Hint: If we changed the number of batteries, would the flow of electricity remain the same?)

DEFINITION: Resistance: The official term for what we have been calling "obstacleness" is electrical resistance. Electrical resistance is measured in units of ohms.

In considering this definition, rewrite this general rule.

General Rule #1: The greater the (fill in the blank) in a circuit the (fill in the blank) the flow of electricity.

This partial rephrasing of the rule is not particularly difficult. The first blank is usually filled-in by the students with the word "resistance" and the second one as before.

What should we be assuming remains the same in this case?

Again it is important for the students to remember that the rule only holds if we do not change the number of batteries and, therefore, their oomph.

## Investigation E3: Capacitors and their Effect on Electricity

Goals: See what the behavior of a circuit containing a capacitor might imply about the nature of electricity.

Apparatus Note: The first capacitors consisted of two sheets of metal separated by a piece of glass. Originally the glass was shaped like (and was) the bottom of a glass jar, but a version was also used in which two parallel metal plates were separated by a flat sheet of glass. From this latter version we get the name for a common type of capacitor-the parallel plate capacitor-and the symbol used to represent capacitors in circuit diagrams, viz:

Most modern capacitors, including those that we use at the beginning of this investigation-the NEC SuperCap™ Capacitor-do not look like the early capacitors, or the symbol, but do have the same fundamental structure and behavior. Later we will use a pie-plate capacitor that does look (somewhat) like the early capacitors.

### Activity E3.1: A Capacitor and How It Affects a Circuit

(Laboratory Activity)

Focusing Question:
If we put a capacitor in our circuit with battery, switch, and bulb, would the bulb light?

Equipment: 4 batteries (D-cells), 1 battery holder, 1 NEC SuperCap™ Capacitor (0.49 F, 10V), 1 compass, 1 tap switch, 1 bulb (oblong #47), 1 bulb socket, and wires (a 12-pack of wires with alligator clips on each end).

At this point please consider, but DO NOT ASSEMBLE the following circuit.

1. WHAT'S YOUR IDEA? First, do you think the bulb would light when the switch is closed? If you think so, on the diagram draw arrows to represent how you think electricity moves about in the circuit as you did in Electricity Investigation 1. (Please note that we have the switch and bulb connected between the negative (-) end of the battery and the capacitor.) If you do not think the bulb will light, then indicate that. In the space below, describe why you think that your answer makes sense and how you think the capacitor might play a role in the behavior of the circuit.

2. WHAT ARE THE GROUP'S IDEAS? Listen as the members of the group describe their ideas about the movement of electricity in the circuit and the role of the capacitor in their predictions. Pay careful attention to their reasons behind their explanations. Try to come to some consensus. Describe the group conclusions in words below and sketch a diagram which indicates the group's ideas about how the electricity flows in the circuit. Include reasons why this consensus seems reasonable. If you cannot come to a consensus, then make a list of the possibilities and the reasons why each possibility seems reasonable. Use the back of the previous page if necessary.

SETTING UP: When the members of the group are pretty sure of their ideas, carefully carry out the following steps:

First, to prepare your NEC SuperCap™ capacitor for use, take a wire and clip each end to separate terminals of the capacitor. This is called "initializing the capacitor." After leaving the wire across the capacitor for about 30 seconds, remove this wire before continuing the activity.

From time to time, when working with capacitors in this unit, you will be asked to "initialize the capacitor."

Now, assemble the circuit as illustrated, but do not test it yet by closing the switch. Please make sure that the switch and bulb are on the negative side of the battery as illustrated in the diagram.

Place a compass between the switch and the light bulb at point A, so you can observe its behavior.

3. MAKING OBSERVATIONS: Close the switch and hold it shut for 20 to 30 seconds and observe what happens to the lamp and compass during that time. If you wish to see it again, you can do so by first initializing the capacitor (This can be done with the NEC SuperCap™ in the circuit, just clip another wire across it for about 30 seconds, then remove this wire.) and then closing the switch again. Discuss what you saw with your lab partners and record it in the space on the next page.

Bulb behavior:

Compass behavior: (cw or ccw? and deflection?)

Try closing the switch a second time without initializing the capacitor. Record what happens.

Now initialize the capacitor as described on the previous page and try again, but this time record the time that it takes for the bulb to go out and the compass needle to relax back to its original position. Repeat the process several times.

Bulb behavior and time to dim out:

Does it appear to be pretty much the same brightness and time to go out each time?

Compass behavior: (cw or ccw? and deflection? and time to relax back?)

Does it appear to be pretty much the same deflection and time to relax back each time?

What do you observe to be the differences between the behavior of the bulb and compass in this circuit with a capacitor and the behavior of the bulb and compass in the circuit with the capacitor removed? You have seen this circuit without the capacitor in previous activities. If you want to check, try the circuit without the capacitor to refresh your memory.

4. WHAT'S YOUR IDEA? In the space below jot down your ideas on these questions. Include the reasons behind your answers to these questions.

5. WHAT ARE THE GROUP'S IDEAS? Share your ideas with your group and see if the group can come to a consensus. Write the group's consensus in the space below.

How might this curious behavior of the circuit with the capacitor be explained? What kinds of things might be imagined about either the electricity or the capacitor that could explain the observations?

6. WHAT'S YOUR IDEA? In the space below jot down your ideas on these questions. Include the reasons behind your answer to these questions.

7. WHAT ARE THE GROUP'S IDEAS? Share your ideas with your group and see if the group can come to a consensus. Write the group's consensus in the space below.