Download Introduction to Electric Fields

Electric Field Lesson Plan
Introduction to Electric Fields
Grade Level: 9 - 12
OBJECTIVES
Following this activity, students will be to:
 Calculate the electric forces on a charge at different locations, given
the magnitude of the electric field at these locations.
 Explain why the electric field of an object does not depend on the
mass of the other charged objects placed in the field. Justification is
based on the field model.
 Compare and contrast the gravitational field of a planet or moon
with an electric field of a charge.
MATERIALS
Each student will be provided the following: Computer with internet connection
 Printer to print and submit the assignment
 Link to the online simulation tool
http://www.compadre.org/osp/items/detail.cfm?ID=10312
 Worksheet for Electric Field (Attached as a separate document)
PREREQUISITE Students should know:
KNOWLEDGE
 The direction of the magnetic field at any location in space is the
equilibrium direction of the north end of a compass placed at that
point.
 The magnetic field strength decreases with increasing distance from
the magnet.
 The gravitational field strength at any point in space around a planet
(or moon, or star) can be measured by hanging a unit mass on a
stationary spring scale.
 The direction of the gravitational field is the direction of a plumb
line, toward the center of the object causing the gravitational.
 Magnetic and gravitational fields can be represented by field
diagrams, obtained by plotting field-strength arrows at different
locations around the object producing the field.
 How to draw force diagrams for mutually attracting and repelling
objects i.e., why forces are drawn from the center of attracting and
repelling objects.
 Coulomb’s Law.
PROCEDURE
The five step procedure of the lesson plan is discussed below:
1. Teacher Demonstration 1
 Using the ElectricField simulator (the link provided in the Materials
section), the teacher shows the students what happens when a small
positive charge, called a test charge, is moved around a positive
*Adapted from http://www.compadre.org/portal/document/ServeFile.cfm?ID=10312&DocID=1816&DocFID=3422&Attachment=1
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Electric Field Lesson Plan

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point charge.
The teacher explains that “The arrow (vector) represents the electric
field strength at a particular location, which is the electric force on
each unit of charge at that location. This can be calculated by
dividing the force by the charge: E = Fe/q. The direction of the field
arrow is the direction of the force on the positive test charge.”
The teacher repeats the demonstration for a negative charge.
Students are asked to complete Question 1 in Worksheet: Electric
Field Simulation.
The figure below shows the simulation screen for demonstration 1.
2. Teacher Demonstration 2
 The teacher turns on the Forces and Test charge grid.
 This field diagram shows the electric field strength of a charge at
several locations around the charge.
 Question: Why are the electric field strength vectors in the field
diagram shorter and shorter as the distance from the charge
increases? “The vectors get smaller because the Coulomb’s law
states that the magnitude of the electric force is inversely
proportional to the square of the distance between two charged
particles.”
 Students complete Questions 2 in Worksheet.
 The figure below shows the simulation screen for demonstration 2.
*Adapted from http://www.compadre.org/portal/document/ServeFile.cfm?ID=10312&DocID=1816&DocFID=3422&Attachment=1
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Electric Field Lesson Plan
3. Collaborative Group Discussion Questions
 The collaborative group discussion questions in the class are as
follows:
 Does the electric field of a charge depend on the mass of the charge
or the mass of the test charge?
 Does the electric field of a charge exist even if there are no test
charges?
 Students fill in Question 3 in worksheet.
4. Concept Development
 Groups share their responses and reasoning to the two questions,
and teacher leads the class discussion.
 The correct response is “The field of a charge is always there, even
if the charge is not interacting with any other charges. The
magnitude of the field at any location depends only on the
magnitude of the charge, not on the mass of the charge.”
 Students fill in Question 4 in Worksheet.
 Teacher demonstrates how to use the Electric Field simulator to
determine the electric field strength (E) at different locations around
a positive charge, and how to calculate the electric force on a
specified charge placed at these locations.
 Students complete Question 5 in their Worksheet.
5. Application of Concepts
 Activity 2 - Forces on a Positive Charge in the Field of a Positive
Charge.
 Students in collaborative groups use the Electric Field Simulation to
determine the electric field strength of a positive charge at two
different locations around the charge.
 Students then calculate the electric force on a specified charge
*Adapted from http://www.compadre.org/portal/document/ServeFile.cfm?ID=10312&DocID=1816&DocFID=3422&Attachment=1
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Electric Field Lesson Plan
placed at these locations.
 For each location, students draw a force diagram of the two charges.
Students complete Questions 6-9 in their Worksheet.
 Teacher leads a class discussion of group results, including the force
diagrams.

Activity 3. Forces on a Positive Charge in the Field of a Negative
Charge.
 Repeat of Activity 2 with a negative source charge.
 Students complete Questions 10-13 in their Worksheet.
 Teacher leads a class discussion of group results and a comparison
of the results for Activity 2 and Activity 3.

Activity 4. Comparison of the Gravitational Field of a Planet
and the Electric Field of a Point Charge.
 Students individually complete a table summarizing the similarities
and differences between the gravitational field of a planet and the
electric field of a point charge (Question 14).
 Teacher leads a class discussion of similarities and differences.
The worksheet with the answer key for has been attached as a separate word document.
Lesson Plan Flow Chart
*Adapted from http://www.compadre.org/portal/document/ServeFile.cfm?ID=10312&DocID=1816&DocFID=3422&Attachment=1
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