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SI unit for charge is coulomb ( C )
E = 1.6 x 10^19 C
P = 1.6 x 10^19 C
How much charge in 1 g of iron?
Iron – 26 protons, 26 electrons, 30 neutrons. Mass of an atom of iron is (30+26) x mass =
56 x 10^27kg = 9.52 x 10^26 = mass = 10^22 g
1 gram must have 10^22 atoms – each atom w/ 26 protons or elections therefore the
charges are
26 x 10^22 x 1.6 x 10^19 = 41.6 x 10^3 C
Coulomb’s Law
the law quantifying the force acting btw 2 charges is similar to the one
w/ gravitational forces.
F = k [q1q2]
R^2
K = 8.988 x 10^9 N* m^2 / C^2
Direcetion of force depends on the relative sign of the charges.
Iron 41600 C
2 protons at a distance r from eachother
(9x10^9 * (1.6x10^19 * 1.6 x10^19)) / r^2
Gravity is 1 billion, billion, billion, billion times weaker than electricity!
Electric Field
Start w/ empty space
Than insert a charge somewhere
This charge creates an affect around the space surrounding it. If another charge is present
somewhere in space, it will feel a force due to the first charge. This is called an electric
field.
Given a certain charge distribution, we want to be able to characterize the forces
generated bys cuh charges in an absouluted way.
Operational definition of electric field due to a given charge distribution:
1)
position at P an arbitrary positive test charge q0
2)
measure the electric force F felt by q0
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divide the F by q): this is the value of the field
E= F/q0
Units of electric field : N/C
Electric field genereated by a point charge:
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 Spring '08
 Conetti
 Physics, Charge, Mass, Neutron

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