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 electrical engineers research, design, develop, and install electrical systems for everything from digital cameras, roller coasters, communication systems, and huge power grids that light up cities to devices smaller than a millimeter that tell a car’s airbag when to inflate.

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:

• Ohm’s Law shows that the change in current is proportional to the change in voltage in a circuit when resistance is held constant.
• The equation for Ohm’s Law is V= IR
• V = voltage in volts, I = current in amps, and R = resistance in ohms. The symbol for ohms is the Greek letter omega, Ω.
• When two resistors are place end to end or in series, they can be thought of as making a single resistor with a greater length.
• When two resistors are placed in parallel, the effect on resistance is similar to using a resistor with a larger diameter.

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

LEARN THE LabLearner LINGO

• There are no new Key Terms introduced in Investigation 2.

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. Student answers may vary.

• How is the current related to the voltage?
• What happens to the current if the resistance changes?

• As a class, briefly summarize what was learned in Investigation One.

Note: In Investigation One, the current was increased in a circuit by increasing the number of batteries. The increase in current was proportional to the increase in voltage. When the resistor in the circuit was changed, the amount of current also changed, but by a smaller amount than in the first circuit. This increase was also proportional to the increase in voltage.

• Ask students to define resistance.

Note: Resistance is the slowing of electrons in a circuit.

• Ask students to explain Ohm’s Law and the equation which represents this Law.

Note: Ohm’s Law states that current increases proportionally as voltage increases. Ohm’s Law is represented by the equation V = IR, where V = voltage, I = current, and R = resistance. The equation can be re-written as R = V/I, so resistance is the ratio of voltage to current.

• Ask students how they proved that resistance is a constant.

Note: In Investigation One, the ratio of voltage to current was constant in each circuit regardless of the number of batteries.

• Remind students that in Investigation One, resistance remained constant but the current changed when the number of batteries changed, demonstrating that Ohm’s Law was in effect.
• Ask students if they think Ohm’s Law will apply if the resistors change while the number of batteries remains constant.

Note: Student answers will vary.

• Inform students that during this Investigation, they will continue their examination of the relationship between voltage, current, and resistance by studying what happens to current when voltage is held constant but resistance changes.
• 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.