Academic journal article Science Scope

Deriving Ohm's Law Using a Guided-Inquiry Investigation

Academic journal article Science Scope

Deriving Ohm's Law Using a Guided-Inquiry Investigation

Article excerpt

Active learning strategies have been shown to be excellent pedagogical tools, as they keep students engaged in a lesson (Michael 2006). Prior research has shown that students are able to construct and retain new knowledge when they are directly involved in creating those connections, as opposed to listening passively to explanations or presentations from the teacher (Freeman et. al. 2014). This article describes a middle school science activity based on Ohm's law that asks students to derive the mathematical relationship between voltage and the current flowing through a resistor. At the end of the investigation, they "define" the mathematical relationship of Ohm's law based on experimental and graphical evidence. The entire activity uses a hands-on, guided-inquiry approach where students are given a series of prompts to enable them to carry out their own investigation without being completely left to their own devices. Prior to conducting this activity, it is essential that students know that electricity involves the flow of electrons.

Engage

As a warm-up to the activity to elicit students' prior knowledge, we ask them about their ideas about what "resistance," "voltage," and "current" mean to them. Students come up with various responses such as "things that block" or "resisting change." (Students define the terms after deriving the equation.)

FIGURE 1: Lab instructions

1. Set the knob to 2000 [OMEGA] or x100 or R x 10. Test the resistance of the resistor by touching the multimeter probes to each metal end of the resistor. Record the resistance. (If using x 100, then multiply the signal by 100, if using R x 10, multiply the signal by 10.)

2. Set up the circuit shown in Figure 2a.

3. Set the multimeter to 20 or 10 in the DCV section.

4. Touch the multimeter probes to each metal end of the resistor. Record the voltage.

5. Open the circuit by undoing one of the clamps on the battery.

6. Add another battery by sliding another battery holder into place.

7. Close the circuit then test and record the voltage.

8. Open the circuit, add a third battery, and repeat.

9. Add the multimeter to the circuit (after opening the circuit) as shown in Figure 2b, but only use one battery.

10. Switch the knob to 200m or 250 in the DCA or DCmA section. Record the current in amps. (Remember, the number shown is in milliamps, not amps.)

11. Open the circuit, add a second battery as shown in Figure 2b, and record the amps.

12. Repeat with a third battery.

13. Graph the data in Excel using voltage as the x-axis and current as the y-axis.

14. Add a trend line (line of best fit) and record the equation (y = mx + b).

15. Answer the postlab questions on your lab paper.

To enhance connections to everyday life, we ask students to think about how water flows from a higher level to a lower level and the idea that something flows because there is a "potential difference" between two points. We ask students to imagine that they are trying to push water through a straw or a hollow pipe containing debris. The debris represents the "resistance" the water will experience. The force needed to push the water through to the other end represents the potential difference. The actual amount of water that can flow through indicates the current flowing through the straw. To enhance understanding of what to expect during the activity, we ask students to predict what will happen to the flow of water if the amount of debris is increased or decreased. Would the flow of water be affected if there were a stronger pump pushing the water through or if there were a mechanism in place to pull the water faster from the other end? Students predict what they would see based on previous experiences. These imaginative scenarios force students to predict what they would expect to see based on their previous experiences. …

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