PHYS 142 Lecture Notes - Lecture 2: Electric Field

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PHYS 142: Electromagnetism and Optics - Lecture 2: Coulomb’s Law and the Electric Field
Coulomb’s Law:
When two charged particles of respective charges q1 and q2 are a distance r apart, each
particle exerts a force on the other of magnitude:
kq1¿q2¿
r2
F=¿
K is called the electrostatic constant. In SI units K = 8.99×109 N m2/C2.
These forces are equal in magnitude and opposite in direction; they are directed along the
line joining the two particles. They are repulsive for two like charges and attractive for two
opposite charges.
Another way to write Coulomb’s law is:
¿q1¿q2¿
r2
F=1
ϵo
¿
where
ϵo=¿
8.85×10-12
C2/Nm2
ϵo
is called the permittivity constant
Electric forces can be superimposed (addition of vectors)
The Electric Field:
Consider the space surrounding a charge Q1. Any charge q placed in that space will
experience an electric force. We can calculate the electric force acting on q at any point in
space. The collection of all these force vectors is the electric field created by a charge Q1.
A charged particle with charge q at a point in space where the electric field is experiences
an electric force:
Fon q =q
E
Thus, the electric field can be represented as:
E=kq
r2
̂
r=1
ϵo
q
r2
̂
r
where
̂
r
represents the direction
The SI unit of electric field is N/C
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Document Summary

Phys 142: electromagnetism and optics - lecture 2: coulomb"s law and the electric field. When two charged particles of respective charges q1 and q2 are a distance r apart, each particle exerts a force on the other of magnitude: k q1 q2 r2. In si units k = 8. 99 109 n m2/c2. These forces are equal in magnitude and opposite in direction; they are directed along the line joining the two particles. They are repulsive for two like charges and attractive for two opposite charges. Another way to write coulomb"s law is: Electric forces can be superimposed (addition of vectors) is called the permittivity constant. Consider the space surrounding a charge q1. Any charge q placed in that space will experience an electric force. We can calculate the electric force acting on q at any point in space. The collection of all these force vectors is the electric field created by a charge q1.

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