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Transcript
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 1 Electric Field Lesson Plan 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 2 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 3 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. *Adapted from http://www.compadre.org/portal/document/ServeFile.cfm?ID=10312&DocID=1816&DocFID=3422&Attachment=1 4