Coulomb’s Law of Force - Complete Toolkit

Objectives

1. To understand that objects are charged if there is an imbalance of protons and electrons and to calculate the amount of charge on an object if given the number of excess protons or electrons.
2. To use Coulomb’s Law equation to make predictions of the effect of alteration in the quantity of charge or the separation distance upon the amount of electrostatic force.
3. To use Coulomb’s Law equation to algebraically solve for an unknown quantity (F, d, Θ₁ or Θ₂) in a physics word problem.
4. To combine Coulomb’s Law equation with Newton’s second law, free-body diagrams and trigonometric functions to analyze physical situations that include interacting charges.

 

Readings from The Physics Classroom Tutorial

1. The Physics Classroom Tutorial, Static Electricity Chapter, Lesson 3

 

Interactive Simulations

1. Coulomb’s Law Interactive
   
   Many students can do the math involved with Coulomb’s equation, but may have little comprehension of its significance. This simulation lets students visualize charge interaction to see why Coulomb’s Law works mathematically. Switch the sign of the charge, change quantity of charge, and move the charges around on a grid. Students will see a mathematical pattern emerge that relates force to separation distance and magnitude of charge.
   
   
   
    
2. PhET:  Charges and Fields
   
   In this model, learners move charges around a simulated electric field to determine how certain variables affect interactions among charged bodies. First, drag a positive or negative charge (or both) onto the field, then place small positive test charges. Drag a sensor to display the voltage at any point on the field or plot equipotential lines. A virtual tape measure is also provided to calculate distance. Force vectors are automatically generated. Register with PhET (it’s free) to access a set of teacher-contributed lessons, Student Guides, and Power Point presentations developed specifically to go with this simulation.
   
   
    
3. Point Charge Forces in 1D Model
   
   This very simple Java model investigates the electric force that one particle exerts on another. It promotes understanding of Coulomb’s Law in three ways:  1) Vector arrows provide a visual way to connect the magnitude of force with changing position; 2) Particle 2 can be dragged left or right to sample the force at various locations; and 3) A graph can be displayed that shows electric force as a function of time. Force values are generated in a table. 
   
    

 

Video and Animations

 

Labs and Investigations

Digital Labs

Demonstration Ideas

 

Minds On Physics Internet Modules:

The Minds On Physics Internet Modules are a collection of interactive questioning modules that target a student’s conceptual understanding. Each question is accompanied by detailed help that addresses the various components of the question.

1. Static Electricity, Ass’t SE8 -  Coulomb’s Law Equation as a Guide to Thinking
    
2. Static Electricity, Ass’t SE9 -  Coulomb’s Law Calculations

 
 
 

Concept Building Exercises:

1. The Curriculum Corner, Static Electricity, Coulomb’s Law

 

 

Problem-Solving Exercises:

1. The Calculator Pad, Static Electricity, Problems #1 - #14
   
   Link: http://www.physicsclassroom.com/calcpad/estatics

 

 

Science Reasoning Activities:

1. Science Reasoning Center, Electrostatics, Charge Interactions
    
2. Science Reasoning Center, Electrostatics, Sticky Tape Experiments
   
   Link: http://www.physicsclassroom.com/reasoning/electrostatics

 

Historical Connections:

1. Charles-Augustin de Coulomb
        
   This short biography from Magnet Academy at Florida State University takes a look at the contributions of Charles Augustin de Coulomb, the 18^th Century French scientist whose experiments with a torsion balance gave rise to one of the fundamental principles of electromagnetism. Coulomb’s Law defines the mathematical relationship between electrically-charged particles and was a cornerstone in the development of electromagnetic theory.
   
   
   
   
   
   
   
    
2. Magnet Academy:  The Torsion Balance 
   
   This tutorial from the National High Magnetic Field Laboratory explores the historic instrument known as a torsion balance. By carefully recording the measurements obtained with a torsion balance, Coulomb was able to establish the law that bears his name. 
   
   
   
   
   
   
    

Common Misconception:

1. A Coulomb of Charge
   
   Students mistakenly believe that a Coulomb of charge is a small amount of charge. After all, “there is just 1 coulomb … not 20 or 200 or 2 million.” Convince students that a Coulomb of charge is a very large amount of charge by calculating the force of interaction between two balloons with a Coulomb of charge located at your school and some distance away at the next nearest high school. The calculation quickly convinces students that a Coulomb of charge is a very large amount of charge. An object with 1 C of charge has gained or lost 6.25x10¹⁸ electrons. For comparison sake, briskly rubbing a balloon on your head 10 times may contribute 2-trillion (2x10¹²) electrons to the balloon. This figure is far short of the 6.25x 10¹⁸ electrons required for a Coulomb of charge. The fact that a Coulomb of charge is a large amount of charge explains why many Coulomb’s law problems express the quantity of charge in units of microCoulombs (µC) and nanoCoulombs (nC).
   
   
   
    
2. Separation Distance
   
   The Coulomb’s Law equation presumes that charged objects act as point charges, with all their charge concentrated at a point. As such, the separation distance d in the Coulomb’s law equation is the distance between these two points. Since objects generally do not occupy points in space, it is important that the measurement of separation distance be made from the centers of the two interacting objects (or at least from the centers of their charge). Students often self-define separation distance to be the distance between the nearest edges of the two interacting objects. 
   
    

 

Elsewhere on the Web:

1. MIT Open Courseware:  Coulomb’s Law Lecture Notes
   
   This is a freely-accessible chapter from MIT’s TEAL Project (Technology Enabled Active Learning) related to Coulomb’s Law. The 45-page document takes a deep dive into the Coulomb interaction for two point charges, as well as multiple charges. It’s a great resource for teachers wanting to brush up or broaden their understanding of electric dipole, forces on charged particles, and problem-solving with 3-and 4-point-charge systems.
   
   
   
    
2. CASES Online:  A Tale of Two Charges
   
   This activity developed for Emory University’s Cases Online presents a unique task: Write a 21^st-Century encyclopedia article about Coulomb’s Law. The article must be scientifically accurate and provide links to digital media that illustrate the concept (to include animations, simulations, and tutorials). Teacher-generated ideas are kept to a minimum, challenging students to locate, analyze, and evaluate resources themselves.  Editor’s Note: Access to CASES Online is free, but requires user registration to open lesson plans and Student Guides. 

 



 

Standards:

A. Next Generation Science Standards (NGSS)
 

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

• HS-PS2.B.1:  Coulomb’s Law provides the mathematical model to describe and predict the effects of electrostatic forces between distant objects.
• HS-PS2.B.2:  Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. 

• Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanation of phenomena.
   

• The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs. 
•  Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small.
   

• Complex and microscopic structures and systems can be visualized, modeled, and used to describe how their function depends on the shapes, composition, and relationships among its parts, therefore complex natural structures/systems can be analyzed to determine how they function. 

• Construct an explanation that includes qualitative or quantitative relationships between variables that predict phenomena.
• Construct and review an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, simulations, and peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

• Develop and/or use a model to generate data to support explanations, analyze systems, or solve problems.
• Use a model to provide mechanistic accounts of phenomena.

• Evaluate the validity and reliability of multiple claims that appear in scientific and technical texts or media reports, verifying the data when possible.
• Critically read scientific literature adapted for classroom use to determine central ideas and obtain scientific/technical information. 

• Use mathematical representations of phenomena to describe explanations.
• Create or revise a simulation of a phenomenon, designed device, process, or system.