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SMC|Academic Programs|Physical Sciences|Predicting E and V for charge distributions

Predicting E and V for charge distributions

EM Field Laboratory

PURPOSE:

To qualitatively investigate how the electric field and electric potential vary around charges and charge distributions.

PROCEDURE:

1. In the box below, draw a sketch of your prediction of the electric field around a +5 point charge. Also think about the electric potential and draw lines that connect five different sets of points that have equal potential. These are called equipotential lines or equipotentials. (So you should have drawn five different equipotentials.)

 

 

 

 

 

 

 

 

 

 

 

 

2. Describe in words how and why you expect the electric field to vary as you move around and away from the +5 charge. Also describe how and why you expect the electric potential to change as you move around and away from the +5 charge.

 

 

 

 

 

 

 

 

 

 

 

 

3. In the box below, draw a sketch of your prediction of the electric field around a -5 point charge. Also think about the electric potential and draw lines that connect five different sets of points that have equal potential - that is, five different equipotentials.. 

 

 

 

 

 

 

 

 

 

 

 

 

4. Start the EM Field Program (either on the desktop or in the Vernier folder under Programs.)

5. Choose "Point charges" under the "Sources" menu choice. Also choose "Show Grid" under "Display".

6. Place one +5 source in the middle of the screen. By clicking on the screen at the positions shown below, show the electric field vectors. Click on the same locations to find the electric potential values. Click on points to draw five different equipotentials around the charge. In the box below draw the electric field vectors, electric potential values and equipotentials that you saw.

 

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

7. Remove the +5 and place one -5 source in the middle of the screen. By clicking on the screen at the appropriate positions, show the electric field vectors. Click on the same locations to find the electric potential values. Click on points to draw five different equipotentials around the charge. In the box below draw the actual electric field, electric potential and equipotentials that you saw.

 

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

8. What do you notice about the values of the electric potential for the -5 charge compared to the +5 charge? Give an explanation.

 

 

 

 

 

 

 

 

 

 

9. In the box below, draw a sketch of your prediction of the electric field around a dipole made of +5 and -5 point charges. Also think about the electric potential and draw lines that connect five different sets of points that have equal potential.  Make predictions for the VALUES of the potential, given your results from Q6, Q7 and Q8.

 

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

 

 

10. Place one +5 and one -5 source horizontally in the middle of the screen. By clicking on the screen at the appropriate positions, show the electric field vectors. Click on the same locations to find the electric potential values. Click on points to draw at least five different equipotentials around the charge. In the box below draw the actual electric field, electric potential values and equipotentials.

 

 

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

 

11. Open the File "QPLATE.EMF" under the menu choice "File" and "Get charges or currents from file". (This represents a plate of positive charge, seen edge on.) Make a PREDICTION as to the electric field and five equipotentials for the indicated points below.

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12. Use the EM Field program to actually find the electric field, electric potential values and equipotentials predicted above.

 EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12. Open the File "QPLATES.EMF" under the menu choice "File" and "Get charges or currents from file". (This represents a capacitor, seen edge on.) Make a PREDICTION as to the electric field, potential values and equipotentials at the same points as was indicated in the picture above.

EM FIeld Diagram

 

 

 

 

 

 

 

 

 

 

 

 

13. Use the EM Field program to actually find the electric field, electric potential values and equipotentials predicted above for the capacitor.

 EM FIeld Diagram


 

 

 

 

 

 

 

 

 

 

 

 

14. Make some comments or observations about electric fields and electric potential in the box below.