Energy and the Environment Activities: Division III and IV

Activity 1: Building the Circuit for your Headlamp

Integration Notes:
This activity has the students construct the circuit that will be used in their headlamps. Students will then examine the construction of an actual headlamp, so that they see how the focal point of the headlamp is adjustable from a near, to a far away focus.

Learner Outcomes:
Students will:

• Construct a circuit using the materials outlined below.

Materials:

• 2 D-cell batteries
• Coated wire (approximately 50 cm, though students will determine how much they will use)
• 3 watt light bulb
• Bulb holder (optional - the students may want to construct their own bulb holder)
• 15 x 30 cm piece of cardboard (thinner cardboard will work fine)
• Tape, glue, scissors

Introduction:
In this activity students will construct the circuit that will be used in their headlamps. The bulb will probably be separated from the batteries, since the bulb is worn at the front and the batteries are usually housed in a battery case at the back of the headlamp.

Activity Instructions:
1. Show a diagram or picture of a headlamp so students are familiar with the basic design. Compare a headlamp to a flashlight and list differences and similarities. Identify that the battery compartment is separate from the bulb, and that you turn on the headlamp by turning the plastic that surrounds the bulb.

2. Construct the circuit for the headlamp using the materials listed above. The steps that follow describe how to make each part of the headlamp. At the end of the lesson all of the parts will be put together to finish the circuit.

3. Bulb and Bulb Holder: Construct the circuit by placing the bulb in the bulb holder and attaching a wire to one of the contact points.

4. Battery Compartment: Construct the battery compartment. It is much more comfortable for the wearer of the headlamp if the batteries are side by side, rather than stacked on top of each other, so construct a box wide enough and deep enough to hold 2 D-cell batteries side by side. The template below shows one possible outline for the box (students can determine the dimensions of the box).

5. Contacts Inside the Battery Compartment: Connect the negative terminal of one battery to the positive terminal of the other battery. This may be accomplished either by using a short length of wire or by using aluminum foil. Aluminum foil is preferable because it is wider and contact between the foil and the batteries will be easier to maintain.

Cut a 12 x 6 cm piece of aluminum foil and fold it in half lengthwise two times so that it is 12 cm long and approximately 1.5 cm wide. Bend the foil so that it sits between the batteries and connects the negative terminal of one battery to the positive terminal of the other. See the adjacent diagram.

6. Connecting the Batteries to the Bulb Holder: Strip the coating off of the ends of two lengths of wire. Tape one wire to the inside of the box where the positive terminal of one battery is, and tape the other wire to the inside of the box where the negative terminal of the other battery will contact it.

7. Complete the Circuit: Connect one of the wires from the battery compartment to the empty contact point at the bulb. Connect the other wire from the battery compartment to the wire leading from the bulb holder. This completes the circuit and turns the bulb on.

Extension Ideas
Students can use other materials such as plastic to construct a more durable, stronger battery compartment. Inventing a way to keep the batteries secure inside the battery compartment may be a relatively simple extension activity.
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Activity 2: Designing a Unique Switch

Integration Notes:
This activity follows up on the last activity where the students constructed the circuit for their headlamp. The next activity will have students use what they have constructed in Activities 1 and 2 and continue to develop their headlamp.

Learner Outcome:
Students will construct a unique switch for their headlamp.

Materials:

• Circuit from Activity 1 "Building the Circuit for your Headlamp"
• Coated wire
• Aluminium foil
• Toilet paper or paper towel rolls or thin cardboard that can be rolled into tubes (one tube should be shorter than the other)
• Tape, glue, scissors
• Any other materials that students require (string, paper clips, etc.)

Introduction:
The activity instructions below give a possible solution for the students when they construct their own unique switch. The switch is a sliding switch, where a tube is placed inside another tube. When the inside tube reaches a certain point, the circuit is completed and the light turns on. The crucial part of this switch is that the inside tube moves inside the outer one. This feature will later allow the students to adjust the focal point of the light coming from the headlamp.

The switch detailed below is not the only solution. Students should be encouraged to design their own switch, though if they are stuck the switch that is described below may give them some ideas to build on.

Remind students that the actual headlamp is turned on and off by rotating the front part of the headlamp (rather than sliding one tube inside another). Rotating the headlamp further allows the user to adjust the depth of focus of the light coming from the headlamp.

Activity Instructions:
1. Cut two pieces of aluminum foil to act as the actual switch. Both pieces of foil should be approximately 1 to 1.5 cm wide. The foil for the inner tube must be shorter than the foil for the outer tube. When the inner tube is slid inside the outer tube and the two pieces of foil come in contact with each other, a circuit will be completed and the light will come on.

2. If students can not find two tubes which fit snugly inside each other they will have to make a tube using a rolled up piece of thin cardboard. Use string to determine the circumference of one tube and construct the other one to be slightly larger or smaller, ensuring that they fit together snugly. They could also measure the diameter of one tube and use the formula C = pd to determine the circumference of the other tube.

3. Attach the stripped ends of coated wire to both pieces of foil before they are glued to the cardboard tubes. Use tape or glue to do this, but keep the foil as flat as possible so that the tubes will slide within each other.

4. Take the foil with the wire attached to it, and attach it to the cardboard tubes. Glue the foil to the outside of the inner tube, and the inside of the outer tube. Keep the foil as flat as possible.

5. Slide the inner tube inside the outer tube. Ensure that they slide relatively easily but still tightly enough so that the inner tube will not fall out of the outer tube.

6. Disconnect the circuit the students made in Activity 1 by disconnecting one of the wires from the contact point at the bulb. In order to insert their switch into their circuit, attach a wire from one of the tubes to the contact point at the bulb, and attach the wire from the other tube to the wire leading from the battery compartment. The arrangement is shown in the adjacent diagram.

Extension Ideas
Alternative switch: Students may want to try to devise a switch that operates like a screw, where the inner tube screws inside the outer tube. This type of switch is more like an actual headlamp and may be constructed by taping string onto the tubes in a spiral pattern to form threads. Two pieces of string may be taped parallel to each other onto the inner part of the outer tube in a spiral pattern. Make sure that there is just enough distance between them to allow a piece of string that is taped to the outside of the inner tube, to fit between them. Encourage the students to develop other ways of constructing a unique switch.
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Activity 3: Making the Headlamp Adjustable

Integration Notes:
This activity will have the students build a reflective cone for their headlamp and devise a way to make the distance that the light is focused away from them variable.

Learner Outcome:
Students will:

• Construct a reflective cone to better focus the light from their headlamp.
• Locate the center of a circle using chords and their perpendicular bisectors (optional outcome).

Materials:
For the small group activity:

• Naked light source (don't use a flashlight or any other light source that has a reflective surface behind it) - a small lamp without the shade would work well
• A piece of thin cardboard approximately 30 x 30 cm
• Aluminium foil
• Tape, glue, scissors

• Circuit from Activity 1 as well as the switch they devised in Activity 2
• Aluminium foil
• Thin cardboard (the size depends on how large the cone will be)
• Tape, glue, scissors

Introduction:
This activity starts out as a small group activity, where the groups of students examine how a reflective cone affects the light emitted from a light source. Before working on their own headlamp, the groups will carry out a larger scale activity where it is easier to manipulate the reflective cone, and easier to notice the effect that changing the arrangement of the cone and light source has on the beam of light.

The students will determine that moving the reflective cone back and forth with respect to the light source changes how far away the light is focussed. Once they have determined this principle, they can use it to make the beam from their headlamp adjustable.

Activity Instructions:
Small Group Activity Instructions:

1. Form groups of two or three students. Cut a large circle out of the cardboard.

2. Glue aluminum foil to the circular piece of cardboard and then trim off the excess foil.

3. Locate the center of the circle. One interesting way of doing this is to draw two separate chords anywhere in the circle. Draw a perpendicular bisector through each chord (a perpendicular bisector is at right angles to the chord and it divides the chord exactly in half). The point where the two perpendicular bisectors meet is the exact center of the circle.

4. After finding the center, cut a straight line from anywhere on the edge of the circle to the middle.

5. Cut out a hole in the middle of the circular cardboard so that the hole is large enough to fit over the light socket of the light source being used.
6. Overlap the two flaps of cardboard enough that the cardboard will form a cone (with a hole at the tip). Use tape to fix the two flaps together so students can adjust the size of the cone and examine the effect on the light.

7. Place the cone over the light source (students may have to remove the bulb first, place the cone over the socket and then replace the bulb). Darken the room and move the reflective cone back and forth to change the depth of focus for the light. Change the diameter of the cone and examine the effects on the light.

This part of the activity could be left up to the students as an exercise in problem solving. Ask the students to use the ideas from the small group activity to design an adjustable headlamp. Let them devise a way to make it work. Suggestions may be needed and there will probably be mistakes made, but the students can reasonably be expected to construct a headlamp that works and is adjustable. If you choose not to have the students solve the problem on their own, the steps that follow can be used as a guide in developing a workable design.

1. Construct a smaller reflective cone (as was done in the small group activity).
2. Attach the sliding switch that was described in Activity 2 directly to the bulb holder and reflective cone. When the tubes are slid, one inside the other, the light bulb will remain stationary and the reflective cone will move back and forth. This back and forth motion of the reflective cone will focus the light either farther away from or closer to the light source.
3. Modifications may need to be made to the switch so that there is less movement of the reflective cone. The cone does not need to move back and forth very much in order to refocus the light, so the tubes may need to be shortened and the aluminum foil contacts may need to be adjusted.

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