Energy and the Environment: Division II

Activity 1: Resistors

Integration Notes:
Students will examine the effect that a resistor has on the amount of current flowing through a circuit. This activity is designed to provide the students with the skills and knowledge needed to construct a headlamp that uses an LED (Light Emitting Diode) as a light source.

Learner outcomes
Students will:

• Examine the effect that a resistor has on the amount of current flowing through a circuit.
• Determine how to manipulate the resistance in a circuit.

Materials:

• pencil or a length of #2 pencil lead
• 6 volt battery
• wires with alligator clips
• small light bulb (6 volts would work well)

Introduction:
In this activity students will make a dimmer switch to change the intensity of a light bulb. In previous activities, students examined conductors. This activity examines semiconductors. Semiconductors conduct electricity, but not as well as conductors. They can also be considered a resistor. This resistor activity will show that as the length of the semiconductor changes, the brightness of the bulb changes.

George Simon Ohm (1785 - 1854) was the first person to publish the results of experimentation on the resistance of wires of various sizes. Ohm constructed wires of many different lengths and thicknesses. Today, we simply call these devices resistors because all they do is resist the flow of current. Ohm applied a potential difference (voltage) across his wire resistors and measured the current through them. He discovered that for each resistor, no matter what potential difference he applied, the resistance was the same.

Resistors are very important in circuits. (see Electricity Background, Ohm's Law They are used to control current or potential difference in a circuit. For example, if you connect an LED to a battery (cell) you will likely destroy the LED unless you have a resistor in the circuit to control the potential difference over the LED. (see Electricity Background, Sources of Light)

Activity Instructions:

1. Before beginning this activity, prepare the pencils. Using a utility knife, cut half of the wood away so that the lead is exposed. If you are not comfortable with cutting pencils, it is possible to purchase pencil lead. (Note: 0.5 and 0.7 mm lead is too small and breaks easily).

2. Create a complete circuit with the bulb, battery and wire. (see Electricity Background, Electric Circuits) Have students note the brightness of the bulb. This can be accomplished by noting the number of sheets of paper the light shines through.

3. Perform the same procedure with the wire touching both ends of the pencil. You can compare how the length of this semiconductive material changes the luminosity of the bulb. Record this information in a table with two columns, one for "Length of pencil lead used in the complete circuit (cm)" and one for "Brightness of Bulb (# of sheets of paper)." Then graph this inverse relationship.

Extension Ideas:

Compare different materials for their resistive qualities.

Perform this same procedure, but instead of manipulating the length of the resistor, change the thickness i.e. cross-sectional area of it.

Reference:
Electrical Connections, 1991 AIMS Educational Foundation.

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Activity 2: Series and Parellel Circuits

Integration Notes:
Students will experiment with alternative ways of setting up simple circuits. Through this exploration, series and parallel circuits will be understood. This activity gives students the knowledge of circuits needed to successfully complete the challenge at the end of the phase.

Learner outcomes
Students will:

• Construct series and parallel circuits. (see Electricity Background, Electric Circuits)
• State the difference between the two basic types of circuits.
• Use the appropriate symbol to represent an electrical device in a circuit diagram.

Materials:

• wire with alligator clips
• AA batteries (two)
• light bulb (3 volt)
• switch
• index cards
• poster paper
• glue, scissors, ruler, etc.
• resistors

Introduction:
An electrical circuit requires a source of electrical energy such as a dry cell battery. The circuit must have a closed path to connect the components. Although a circuit will function without a switch, it is convenient to have one. You can open and close the circuit with a switch.

A resistor is used to represent any one of many different components, called loads that convert electrical energy into other forms of energy. For example, motors, toasters, light bulbs, and stereos convert electricity into motion, heat and light. There are so many different electrical devices that it would not be practical to use different symbols for each. The resistor represents something that they all have in common. They all resist the movement of charge through a circuit.

In this activity students will experiment with finding as many ways as possible to construct a circuit. They will be asked to incorporate resistors, a light bulb and switch in a variety of ways and organize their circuits into two main types of circuits (series and parallel).

Activity Instructions:

1. Examine the chart below that illustrates the symbols for each component of a circuit. You will be expected to use these symbols in the circuit diagrams that you draw for the rest of this activity.

Component	Symbol
Battery (per cell) - is a combination of cells
Light bulb - is an example of a resistor
Resistor - is anything that resists the movement of charge through the circuit
Switch

2. Collect all of the materials listed above and experiment with arranging them in as many different ways as possible. Each time you construct a new circuit, draw a diagram that represents the circuit on an index card.

3. When you have come up with a few different arrangements and recorded them on index cards, organize the cards into three piles based on the similarities in the arrangement of the components. One pile should contain circuits where all of the components are connected in a linear fashion, or one after another. This pile represents series circuits.

4. The second pile should contain circuits where one or more components branch off from the circuit at the same point. This pile represents parallel circuits. The third pile should contain circuits that are a combination of parallel and series circuits. Make a list of the similarities and differences between the series and parallel circuits.

5. Glue your index cards and list of similarities in the circuits onto a piece of poster paper to make a poster that illustrates the two different types of circuits.

Extension Ideas:

Compare the intensity of the bulb with the different circuits they create. Infer the pros and cons of series and parallel connections.

Use the resistor made in Activity 1 as a basis for an extension activity on the effect of resistors in series or in parallel.

JUMP TO: Activity 1 | Activity 2 | Activity 3 | Challenge | Top

Activity 3: Light Emitting Diodes

Integration Notes:
Students will examine LEDs and how they differ from incandescent bulbs. This activity presents students with the information they will need in order to be successful at the challenge at the end of this phase (construct a headlamp using LEDs).

Learner outcomes
Students will:

• Construct a circuit containing resistors, a battery and four white LEDs.
• Determine the size and amount of resistors needed in a circuit that includes four LEDs.

Materials:

• wire
• three - 1.5 volt batteries in series (a minimum of 3.6 volts is required for most LEDs)
• additional batteries as required
• four white LEDs
• resistor (45 Ohms) - this value is based on providing 4.5 volts of source voltage
• additional resistors

Introduction:
A Light Emitting Diode (LED) (see Electricity Background, Sources of Light) is a special diode that emits light when connected in an electrical circuit. A clear or coloured epoxy case surrounds and encloses a semiconductor chip.

Students will incorporate resistors (see Electricity Background, Ohm's Law) into a simple circuit so that they can use four LEDs to provide light, instead of relying on a relatively power hungry incandescent bulb. The knowledge students gained in Activities 1 and 2 of this phase are vital to this activity if the students are going to construct an effective circuit with an LED without melting it.

Activity Instructions:

Diagram of an LED, provided by theledlight.com. For more on how LEDs work, view the Technical Information from the LED site.

1. Use the knowledge gained in Activities 1 and 2 to construct a circuit using a single LED in a simple circuit. Use a AA battery as a power source and begin with a larger, rather than smaller resistor to prevent melting the LED.

Make sure to insert the LED in the correct orientation since it only works when the current passes through it in a single direction. Experiment to find which way LEDs must be inserted, remembering that the positive is the longer one of the two terminals.

2. Add another LED to the circuit in series and then in parallel and notice the effect on the brightness of the LEDs.

3. Alter the amount of current and the size of the resistor in the circuit to have a working light source with two LEDs. Students can work out the size of resistor they will need to protect the LEDs by using Ohm's Law. (see Electricity Background, Ohm's Law)

For example: