Lectronic Plates Notes.docx - PhET

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					PhyzSim: ’Lectronic Plates Notes (PhET Capacitor Lab v1.00)
UNIFORM ELECTRIC FIELDS

SETUP
1. Launch the PhET Sim: Capacitor Lab. For this activity, remain in the Introduction tab.
2. From the Control Panel View section, activate the Plate Charges option.
3. From the Control Panel View section, Electric Field Lines can be activated or not: your call.
4. Click the on-screen button to Disconnect Battery.
5. Use the on-screen arrow control to set the Plate Area to approximately 200 mm2 (between 195
mm2 and 205 mm2).
                The closest I’ve been able to get is 199.8 mm2
6. Use the on-screen arrow control to set the Separation to 7.5 mm (7.4 mm—7.6 mm).
                7.5 mm can be obtained
7. From the Control Panel Meters section, activate the Electric Field Detector. Make sure the
“Show Values” option is activated. The detector’s sensor should appear between the parallel
plates.
8. Using the on-screen Plate Charge slider, increase the charge until the electric field between the
plates is nearly 1450 V/m (1400 V/m—1500 V/m). Use the detector’s display zoom controls as
needed.
                1444 V/m is a nice round number, but others are acceptable
9. Activate the Plate Charge display.
                A field of 1444 V/m requires a plate charge of 0.26E–11 C

VARY THE VARIABLES
1. What relationship—if any—is there between the plate charge and the resulting electric field?
Describe your evidence.
Electric field is directly proportional to plate charge: E  Q
Increasing plate charge increases the electric field strength.

2. What relationship—if any—is there between the plate area and the resulting electric field?
Describe your quantitative evidence.
Electric field is inversely proportional to plate area: E  1/A
When the area is doubled to 400 mm2, the field decreases to 721 V/m
When the area is halved to 100 mm2, the field increases to 2886 V/m.

3. What relationship—if any—is there between the separation distance and the resulting electric
field? Why do you suppose this surprises some people?
Electric field is independent of plate separation. Some would expect the field
to decrease with increasing separation distance.




The Book of Phyz by Dean Baird: http://phyz.org
CHARGE DENSITY
4. A student suggests that the strength of the electric field is constant for a given charge density.
That is, the plate charge can be varied and the plate area can be varied, but as the electric field
value will remain constant as long as the ratio between the two is constant.
a. The symbol for charge density is  (lowercase sigma). What are the units of charge density?
 = Q/A so its units are C/m2.

b. Cite numerical evidence from sim experimentation to accept or reject the student’s claim.
Accept: The field of 1444 V/m occurs when the charge density
is 0.26E–11 C / 199.8E–3 m2
A field of 1443 V/m occurs when the charge density
is 0.51E–11 C / 400E–3 m2

STRONGEST FIELD
5. What is the strongest electric field you can create in the sim?
6000 V/m
b. Comment on each parameter in the configuration, indicating whether it should be at a
maximum, minimum, or if it’s irrelevant: plate charge, plate area, and separation.
Q: maximum A: minimum d: irrelevant

c. How can you maximize charge density? Discuss in terms of plate charge, area, and separation.
Maximize charge and minimize area; separation is irrelevant.

THE BATTERY
Click the on-screen button to Connect Battery.
6. What is the strongest electric field you can create in the sim with the battery connected?
300 V/m
b. Comment on each parameter in the configuration, indicating whether it should be at a
maximum, minimum, or if it’s irrelevant: battery voltage, plate area, and separation.
V: maximum A: irrelevant d: minimum

c. How can you maximize charge density? Discuss in terms of battery voltage charge, plate area,
and separation.
Maximize voltage and minimize separation; area is irrelevant.




The Book of Phyz by Dean Baird: http://phyz.org

				
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posted:11/2/2011
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