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Electromagnetism in one slide
• Electric charges
q
establish electric fields
E
everywhere
in space.
• An electric charge experiences an electric
force
F
E
=q
E
,
where
E
is the electric field at the charge’s position, and
q
is the magnitude of the charge.
• Moving electric charges result in electric currents;
electric currents establish magnetic fields
B
everywhere
in space.
• A moving charge
q
experiences a magnetic force
F
B
=q
v
×
B
, with
v
the velocity of the charge and
B
the
magnetic fields at the location of the charge.
• Magnetic fields can also be established by
timevarying
electric fields.
Likewise, electric fields result from time
varying magnetic fields.
These coupled effects produce
electromagnetic waves.
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View Full Document Electric charge
•
Protons possess a charge
q
p
=+e
, electrons
q
e
=e
, with
e=
1.6
×
10
19
Coulomb(C).
• Experimentally
q
p
+q
e
/e
<10
21
, the electron charge is
equal and opposite
the proton charge.
• The total charge is
Q=(N
p
N
e
)e
, with
N
p
,N
e
the number of
protons,electrons.
• Ordinary matter is electrically neutral:
Q=
0
, so
N
p
=N
e
.
• In a typical material, water, there are ~10
6
C/mole, or
5
×
10
4
C/cm
3
of proton charge and an equal amount of
electron charge.
Let’s try the clickers
•
How many protons are to needed for 1 C of charge?
A. 1.6×10
19
B. 1
C. 6.2×10
18
D. 6.0×10
25
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View Full Document The Efield of 1 charge
•This is the basic building block of electric fields:
– The first factor is the charge
Q
. Fields point away from
positive charges and towards negative charges.
– The second factor
k=1/4
πε
0
≈
9
×
10
9
Nm
2
/C
2
is, as we shall see,
a measure of how strong electric forces are.
The peculiar
way of writing
k
in terms of another constant
ε
0
=8.85
×
10
12
C
2
/Nm
2
will be explained later.
– The third factor
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This note was uploaded on 05/11/2010 for the course ＰＨＹ 214 taught by Professor Timothybolton during the Spring '10 term at Kansas State University.
 Spring '10
 TimothyBolton
 Charge, Electric Fields, Magnetism, Force

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