Electric Fields and Coulomb's Law

Active learning helps students grasp abstract concepts like charge conservation and energy transfer because circuits allow direct observation of invisible processes. When students manipulate real components and measure changes, they build lasting mental models instead of memorizing formulas.

• Year 12
• Physics
• 3 activities
• 20 min–60 min

Learning Objectives

1. Define electric field strength and state its unit.
2. Calculate the magnitude and direction of the electrostatic force between two point charges using Coulomb's Law.
3. Compare the electric forces acting on charges in different configurations.
4. Explain the concept of an electric field as a region of space where a charge experiences a force.

Stations Rotation

⏱ 60 min·Small Groups

Stations Rotation: Component Characteristics

Students move between stations to measure I-V characteristics for a filament lamp, a diode, and a fixed resistor. They must use their data to explain why some components do not follow Ohm's Law as they heat up.

Prepare & details

Explain how electric current is defined as the rate of flow of charge and derive the relationship I = ΔQ/Δt from first principles.

Facilitation Tip: During Station Rotation: Component Characteristics, place a labeled diagram of the circuit at each station to reduce setup errors and focus attention on the behavior of each component.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Inquiry Circle

⏱ 50 min·Small Groups

Inquiry Circle: The Potential Divider Challenge

Groups are given a sensor (LDR or thermistor) and must design a circuit that turns on an LED when it gets dark or cold. They must calculate the required fixed resistor values before building and testing their design.

Prepare & details

Analyse how the mean drift velocity of free electrons determines current magnitude using I = nqvA, comparing values in metals and semiconductors.

Facilitation Tip: In Collaborative Investigation: The Potential Divider Challenge, assign roles (recorder, measurer, builder) so every student contributes to the data collection and analysis.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Think-Pair-Share

⏱ 20 min·Pairs

Think-Pair-Share: Internal Resistance Mystery

Show a battery measuring 9V when 'open' but 8.5V when connected to a bulb. Students work in pairs to hypothesize where the 'lost volts' went, leading to a class discussion on internal resistance and emf.

Prepare & details

Evaluate how the electron model of conduction accounts for the differences in electrical conductivity between conductors, semiconductors, and insulators.

Facilitation Tip: For Think-Pair-Share: Internal Resistance Mystery, provide pre-calculated examples of expected vs. measured values to guide students toward identifying the mismatch without giving away the answer.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Teaching This Topic

Teach Kirchhoff’s Laws as the ‘accounting rules’ for circuits: charge in equals charge out, and energy in equals energy out. Use analogies like a river’s flow for current and a toll booth for potential drop. Avoid teaching Ohm’s Law as a universal rule; instead, emphasize that resistance is a property of a component, not a circuit law.

What to Expect

By the end of these activities, students will confidently apply Kirchhoff’s Laws to circuit calculations and explain how internal resistance affects terminal potential difference. They will also distinguish between emf and pd using data from their own measurements.

Watch Out for These Misconceptions

Common Misconception

During Station Rotation: Component Characteristics, watch for students who assume the current decreases after passing through a resistor because the voltage drops.

What to Teach Instead

Use the multimeter to measure current at three points in a simple series circuit with one resistor. Have students record the values and note they are identical, then revisit the misconception by asking them to explain why the same number of charges pass each point per second.

Common Misconception

During Collaborative Investigation: The Potential Divider Challenge, watch for students who confuse emf and terminal pd when the circuit draws a small current.

What to Teach Instead

Ask students to measure the emf of their battery with no load and then measure the terminal pd with their potential divider connected. Have them calculate the difference and relate it to the energy ‘lost’ inside the battery, using the formula V = ε - Ir to link the data to the concept.

Assessment Ideas

Quick Check

After Station Rotation: Component Characteristics, ask students to draw a series circuit with three identical resistors and mark the current and voltage at each point. Collect their diagrams to check for correct labeling of identical current values and proportional voltage drops.

Exit Ticket

During Think-Pair-Share: Internal Resistance Mystery, give students a circuit diagram with a battery of emf 6.0 V and internal resistance 2.0 Ω connected to a 10 Ω resistor. Ask them to calculate the terminal pd and the current, then explain in one sentence why the terminal pd is less than the emf.

Discussion Prompt

After Collaborative Investigation: The Potential Divider Challenge, facilitate a class discussion where groups present their findings on how changing a resistor value affects the output voltage. Ask students to explain the relationship using Kirchhoff’s Laws and to predict what would happen if the supply voltage were doubled.

Extensions & Scaffolding

• Challenge: Ask students to design a potential divider that produces a specific output voltage using only two fixed resistors and a thermistor.
• Scaffolding: Provide a partially completed data table for the Potential Divider Challenge with missing values for students to calculate before measuring.
• Deeper exploration: Have students research how a strain gauge works as a potential divider and present a one-slide explanation linking the change in resistance to the change in voltage.

Key Vocabulary

Electric Field	A region around an electrically charged object where another charged object will experience a force. It is represented by field lines indicating direction and strength.
Coulomb's Law	A law stating that the electrostatic force between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.
Point Charge	An idealized electric charge located at a single point in space, with no spatial extent.
Electrostatic Force	The attractive or repulsive force between two electrically charged objects. Like charges repel, and opposite charges attract.