Two Oppositely Charged Parallel Plates
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Consider two metallic plates, each of area A, aligned parallel to one another and separated by distance r, which is small relative to the width of one plate. Evacuate the space between the plates and attach a battery to each, charging one plate with a positive charge of magnitude Q, the other with a negative charge of the same magnitude. The charges create an electric field between the plates and the plates exert attractive forces on one another.
The field Eo between the plates is the surface charge density, that is, it is the charge per unit area on one plate,
Eo = Q/A
Simulation
1. Check the force at point A. Write your observation.
2. Check the force at point B in the simulation. Write your observation.
3. Is the force same at all points between the two plates?
4. What is the force in the outer region of the plates?
Challenge Question
1. Experimenter A uses a very small test charge qo, and experimenter B uses a test charge 2qo to measure an electric field produced by two parallel plates. A finds a field that is
A. greater than the field found by B
B. the same as the field found by B
C. less than the field found by B
D. either greater or less than the field found by B, depending on the accelerations of the test charges
E. either greater or less than the field found by B, depending on the masses of the test charges
Answer: B
An electric field exists regardless of the amount of charge placed in it, and regardless of whether any charge at all is placed in it. So both experimenters must measure the same field (though they will measure different forces on their test charges).
The field Eo between the plates is the surface charge density, that is, it is the charge per unit area on one plate,
Eo = Q/A
Simulation
1. Check the force at point A. Write your observation.
2. Check the force at point B in the simulation. Write your observation.
3. Is the force same at all points between the two plates?
4. What is the force in the outer region of the plates?
Challenge Question
1. Experimenter A uses a very small test charge qo, and experimenter B uses a test charge 2qo to measure an electric field produced by two parallel plates. A finds a field that is
A. greater than the field found by B
B. the same as the field found by B
C. less than the field found by B
D. either greater or less than the field found by B, depending on the accelerations of the test charges
E. either greater or less than the field found by B, depending on the masses of the test charges
Answer: B
An electric field exists regardless of the amount of charge placed in it, and regardless of whether any charge at all is placed in it. So both experimenters must measure the same field (though they will measure different forces on their test charges).