Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ASK WHY

Remind students that electricity is important because it is the most common energy we consume and depend on in our daily lives. We use electrically powered gadgets to communicate, for entertainment, to produce food, and to run our homes. Electricity is even starting to transform our transportation systems.

BRANCH OUT

Remind students that power plant distributor and dispatchers monitor the U.S. power grid to make sure that power generation matches power consumption.

GET FOCUSED

GO DEEPER

As a class, read the Background(s) in the Investigation. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concepts as a class:

• A circuit is an uninterrupted path between the terminals of a power source.
• Each terminal of a battery is connected to a different type of chemical. The chemical at the negative terminal releases electrons, which flow to the positive terminal. The chemical at the positive terminal attracts the electrons released by the negative terminal.
• Electrons flow from the chemical with the higher electric potential to the chemical with the lower electric potential.
• The difference between these two potentials in a battery is called voltage. Voltage is measured in volts (v). Batteries are rated based on their voltage.
• Even though electrons flow from the negative terminal of a battery to the positive terminal, current flows from the positive terminal to the negative terminal.
• Current is the flow of electrons through a circuit. It is measured in units called amps (A).
• Circuits contain a power source, paths for the current to flow, and one or more resistors.
• A resistor is a device in a circuit that slows the flow of electrons. The term resistor can be used to refer to any device in general, such as a light bulb or an electric appliance in a household circuit. However, the term resistor also refers to a special piece of equipment used in electronic devices to control current.
• Scientists use resistance to determine the effect of resistors on the flow of current. Resistance is measured in units called ohms (Ω).
• Physicists and electricians use a special type of diagram called a schematic to represent a circuit.
• A schematic tells the person who is constructing a circuit what components are needed and where to put each component.
• A schematic uses special symbols to represent the components of a circuit.
• A schematic also indicates where any meters should be placed.
• The meter used to measure potential difference (represented by a V for voltmeter) is placed so that the meter is the potential difference across the resistor.
• The meter used to measure current (represented by an A, for ammeter) is placed between the resistor and the negative terminal of the battery.
• In equations and schematics, current is represented by the letter “I”.
• The device used to measure current is represented by an “A”. The “A” stands for ammeter because current is measured in units of amps.
• In the field of electricity there is a law that describes the relationship between the voltage, current, and resistance of a circuit. This law is called Ohm’s Law.
• The equation for Ohm’s Law is V = I x R
• V = voltage in volts, I = current in amps, and R = resistance in ohms. The symbol for ohms is the Greek letter omega, Ω.

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

• current
• electric potential
• multimeter
• Ohm’s Law
• potential difference
• resistance
• resistor

Note: Definitions of these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

SET FOR SUCCESS

• Direct students to complete the Recall section in their SDRs. Students answers may vary.

• What is voltage?
• What is current?
• What is resistance?
• What causes resistance?

• Encourage students to share their ideas about electricity. As a class, discuss students’ prior knowledge of electricity.

Note: Students may describe electricity in terms of sources of power such as power plants and batteries. Students may also describe electricity in terms of current, voltage, circuits, switches, and electrical appliances. Students may indicate that electricity cannot be seen, but that its presence can be detected through the operation of televisions, radios, computers, light bulbs, and other electrical devices.

• As a class, discuss students’ prior knowledge of the concept of electricity as a form of potential energy. Ask students to explain why a battery is a potential source of energy.

Note: Batteries contain chemicals that serve as a source of charges. Each battery terminal is served by a different chemical. When placed in a closed circuit, the charges move through the wires from one terminal to the other. The movement of charges is responsible for generating electricity. Electrons move from the negative to the positive terminal of the battery. The direction of current flow, however, is designated from the positive to negative terminal of the battery.

• The Law of Conservation of Energy states that energy is neither created nor destroyed, it merely changes form. Ask students to explain how the movement of electric charge through a simple circuit of a battery and a light bulb is an example of conservation of energy.

Note: The battery terminals are sources of electrical potential energy. Electrons flow from the negative terminal to the positive terminal through the light bulb. The flow of electrons through the filament of the light bulb causes it to heat and glow, producing light. Heat and light are forms of kinetic energy. The electrons collect at the positive terminal of the battery, becoming potential energy again.

• As a class, discuss students’ prior knowledge of voltage and current. Ask students what they think the difference is between voltage and current.

Note: Student answers will vary. Voltage is the difference in potential between two points. In a battery, the voltage is the difference in potential between the positive and negative terminals. Current is the flow of charges in a circuit due to the difference in potential between the terminals. Current flows from areas of high electric potential to areas of low electric potential.

• As a class, discuss students’ prior knowledge of resistance. Ask students what the term resistance means to them.

Note: Student answers will vary. Some students may suggest that resistance implies an unwillingness to perform a task or change an opinion. Others may equate resistance with an inability of an object to yield, such as a heavy rock remaining still despite a large amount of applied force. The rock is resistant to movement.

• Inform students that in the context of this Investigation, resistance will be used to refer to the ease with which electricity passes through a material.
• Play the video below. Stop to ask students questions or answer students’ questions when necessary. Remind students to follow along with their SDRs and make any notes that they think might be helpful.
• After the video, direct students to divide into their lab groups to discuss their strategy for the lab. For example, they may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow students to anticipate the laboratory experience they will soon encounter. Students should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.

HOMEWORK

Tell students that they should review the Investigation in preparation for the Lab.