Coulomb’s Law Basics

Unit: Exploring Atomic Structures

Lesson: 5 of 10

Duration: 45 minutes

Class Size: 30 Students

Grade: 10th Grade

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NGSS Alignment

Disciplinary Core Ideas (DCI):

• PS2.B: Types of Interactions — Electric forces can be attractive or repulsive, and their strength depends on the magnitude of electric charges and the distance between them.

Science and Engineering Practices (SEP):

• Developing and Using Models
• Analyzing and Interpreting Data

Crosscutting Concepts (CCC):

• Cause and Effect
• Scale, Proportion, and Quantity

Performance Expectations (PE):

• HS-PS2-4: Use mathematical representations of Coulomb’s Law to describe and predict the force between charged objects.

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Learning Objectives

By the end of this lesson, students will be able to:

• Explain the relationship between electric force, charge magnitude, and distance as described by Coulomb’s Law.
• Mathematically represent Coulomb’s Law: ( F = k \frac{|q_1 q_2|}{r^2} ).
• Analyze how changes in charge or distance affect the magnitude and direction of electrostatic forces.
• Apply Coulomb’s Law to solve basic problems involving charged particles.

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Materials Needed

• Whiteboard or smartboard
• Student handouts with Coulomb’s Law formula and example problems
• Small charged objects or simulations (e.g., virtual PhET simulation: “Charges and Fields”)
• Calculators
• Graph paper

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Lesson Procedure

1. Engage (5 minutes)

• Phenomenon Prompt: Show an image or animation of two charged particles either attracting or repelling each other. Ask: What causes charged objects to push or pull one another?
• Solicit quick student ideas and connect their responses to electric forces.
• Set purpose by introducing the term Coulomb’s Law, highlighting that today they will discover how physicists measure that force.

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2. Explore (10 minutes)

• Hands-on Activity: In pairs, students use small charged objects (e.g., balloons rubbed on hair and paper scraps) or an interactive simulation to observe attraction/repulsion at varying distances. Ask students to note qualitative changes in force as distance changes.
• Students discuss with their partner: What happens to the force when distance doubles? What might happen if charge changes?

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3. Explain (15 minutes)

• Direct Instruction:

  • Introduce Coulomb’s Law formula:
    [ F = k \frac{|q_1 q_2|}{r^2} ] where:

    • (F) = magnitude of force (Newtons)
    • (k) = Coulomb’s constant (8.99 \times 10^9 , Nm^2/C^2)
    • (q_1, q_2) = magnitude of charges (Coulombs)
    • (r) = distance between charges (meters)

  • Explain the concepts of electric charge magnitude and distance and how they affect force strength (inverse square relationship).

• Work through 2-3 example problems on the board demonstrating:

  • How to substitute values
  • How doubling distance reduces force by a factor of 4
  • How increasing charge increases force linearly

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4. Elaborate (10 minutes)

• Group Activity:
  • Students work in small groups on a worksheet with 3 problems requiring use of Coulomb’s Law.
  • At least one problem involves changing variables to predict the effect on force (e.g., “If the distance is halved, what happens to the force?”).
  • Encourage students to sketch forces as vectors, including direction (attraction vs repulsion).

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5. Evaluate (5 minutes)

• Exit Slip: Individually, students answer two questions on a small card:

  1. Write the formula for Coulomb’s Law and explain what happens to the force if the distance between two charges doubles.
  2. Calculate the force between two charges of ( +3 \times 10^{-6} C ) and ( -2 \times 10^{-6} C ) separated by 0.5 meters. (Provide constant on sheet if needed)

• Collect exit slips for formative assessment.

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Differentiation Strategies

• For Students Needing Support: Use visual aids and simplified math steps; allow use of calculators; pair with peer tutors.
• For Advanced Students: Provide real-world scenarios involving multiple charges or ask them to rearrange the formula to solve for (r) or (q).

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Reflection and Extension

• Ask students to reflect on how Coulomb's Law relates to atomic structure and forces between subatomic particles (foreshadowing upcoming lessons).
• Extension at home or next class: Investigate how Coulomb’s Law underpins technologies, such as capacitors and electrostatic precipitators.

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Teacher Notes

• Emphasize the importance of units and signs of charges.
• Prior lessons should have introduced electric charges and basic atomic structure for context.
• Ensure students understand vector nature of forces beyond just magnitude.

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This lesson plan carefully integrates hands-on investigations, conceptual understanding, mathematical application, and assessment while aligning strictly with NGSS expectations for HS-PS2-4. It balances engagement and rigor appropriate for 10th graders and paves the way for deeper quantum and electromagnetic studies.