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Coulomb Balance
Performed: 2/1/07, Due: 2/8/07
Theory:
According to Coulomb’s law the magnitude of the electric force between two
point charges is directly proportional to the product of the charges and inversely
proportional to the square of the distance between them. This law manifests itself in the
formula above. The equation shows that 1/ε
0
is the proportionality constant, which for
any charge gives the correct force as the left hand expression of the equation. ε
0
is a
constant known as the vacuum permittivity. The inverse of this permittivity gives the
scale for the strength of the electrostatic interaction between charges.
In a parallel plate capacitor whose dielectric is vacuum or air (we assume
equality), if a voltage (V) is maintained between the plates by a power supply, the plates
will have equal and opposite charges to each other. The opposite charges on the plates
cause an attractive force between them which is given my the second equation, where A
stands for the area of each plate in square meters, V is the potential difference in volts,
and d is the distance between the two plates in meters, and F is the force in Newtons. We
should find that the attractive force is equal to the 50mg mass we place at the center of,
the top plate of the apparatus during setup, allowing us to find experimental values of ε
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 Spring '07
 Budick
 Charge, Force

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