Lab: Storing Energy in Uniform Electric Fields

In this lab you will use the Electric Field, Uniform simulation to determine how a test charge moves in a uniform electric field.

 

Purpose

 

In this lab activity you will use a computer simulation to collect data enabling you to answer the following questions:

  • How does a test charge move in a uniform electric field?
  • How can this motion be explained using physics principles?

Procedure

 

 Step 1: Open the Electric Field Potential, Uniform simulation and enter the settings below. Note that in this simulation the electric field is not varying as it is in the region surrounding a single point charge. The electric field in this simulation is uniform in strength and direction once the “play” button is pressed.

  • Enter the following values for the electric field: 10.0 V/m at 0°. (Note that the unit for field used here,the volt per metre, is equivalent to a newton per coulomb. You will learn more about this later in the lesson.)
  •  Ensure that Electric Field Vector is displayed
  •  Enter the following values for the initial velocity: 5.0 m/s at 0°.
  •  Position the test charge (red dot) to the following location: (x,y) = (100,0).


If you choose to rewind, you can return to these initial settings at any time during this lab
activity. However, if you use the “reset” button, you would have to re-enter all these initial
settings.

Step 2: For the analysis, you must collect the following data from the screen:
    E→ = __________            v→ = ____________
qtest = ___________   mtest = _____________


Step 3: Press play, and observe the motion of the test charge until it reaches the point (x,y) =
(300,0). Then, press the “pause” button. Use “rewind” if it takes several attempts to achieve
(300,0). Record the final velocity for the particle when it has reached (300,0). You will use this value for
the analysis.

vf→= ___________


Analysis

 

Self-Check

Answer the following self-check (SC) questions then click the "Check your work" bar to assess your responses.

 

SC 12.

  1. Calculate the magnitude and direction of the electrostatic force acting on the test charge (+2.0 C) at the starting location (A=100 m) and and the point end point (B =300 m) if the electric field strength is 10.00 N/C.

  2. Draw a free-body diagram to show the force acting on the particle at the points A and B 

  3. Refer to your answer to SC 12.b.  How is this free-body diagram different from the one that you drew in the previous lab activity when the electric field was non-uniform?

  4. Use your values for electrostatic force to calculate the acceleration of the test charge at locations A and B.

   Self-Check Answer

SC 12.

a.

Given

 

Required

The magnitude and direction of the electrostatic force at 100 m and 300 m, 

 

Analysis and Solution
  • The electric field is directed from left to right, so the electrostatic force acting on a positive test charge will also be from left to right.

  • The electric field has the same magnitude in both locations, so the magnitude of the electrostatic force will be the same in both locations for a given test charge.

Paraphrase

The electrostatic force will be 20 N [right] in both locations.



  2.   When the electric field is uniform, the electrostatic force vectors have the same magnitude and direction in all locations. This stands in contrast to the situation in the previous lab activity where the electrostatic force vectors decreased in magnitude as the distance increased from the source.


Given

 

Required

The acceleration of the test charge at 100 m and at 300 m.

 

Analysis and Solution

The acceleration will be the same at both locations because the electrostatic force is the same at each location.

 

 

Paraphrase

The acceleration of the text charge is 6.7 m/s 2  [0°] at both 100 m and 300 m.

  

Conclusion

 

Before continuing to page 10 of this lesson, review the content in the uniform electric field link.