Winter wk 8 – Thus.24.Feb.05 Review Ch.30 – Faraday and Lenz laws Ch.32: Maxwell Equations!...
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Transcript of Winter wk 8 – Thus.24.Feb.05 Review Ch.30 – Faraday and Lenz laws Ch.32: Maxwell Equations!...
Winter wk 8 – Thus.24.Feb.05
Review Ch.30 – Faraday and Lenz laws
Ch.32: Maxwell Equations!
• Gauss: q E
• Ampere: I B
• Faraday: dB/dt E (applications)
• Maxwell: dE/dt B
Magnetism in matter
Energy Systems, EJZ
Gauss: charge q E field
0
E dA encE
q
B dA 0B ��������������
No magnetic charges
Practice: P2 (p.883)
Lenz’s law tells DIRECTION of
Induced emf opposes change in flux:
Induced current Ii creates an induced field Bi to oppose any change in the external flux.
In what direction does current flow, in each diagram?
Bd
dt
Generators & Transformers
cos sind
BA t NBA tdt
N
1 2
1 2
2
1
1 1 2 2
2
1
:
________
________
B
B
d
dtshared flux
d V V
dt N N
V
V
Power I V I V
I
I
V N
AC power depends on transformers
Step-up transformer: higher voltage, lower current
Step-down: lower voltage, higher current
Induced magnetic fields: dE/dt B
BdE ds
dt
����������������������������
Recall Faraday: changing magnetic flux E field
Symmetry: changing electric flux B
0 0Ed
B dsdt
����������������������������
Practice: P 5, 10 (p.884)
Ampere-Maxwell Law
What can cause a magnetic field B?
Ampere: Current IB:
Maxwell: changing EB: 0 0Ed
B dsdt
����������������������������
0 enci B ds ����������������������������
0 0 0E
enc
dB ds i
dt
����������������������������
Practice with magnetic induction
Q1 (p.882): Is E increasing or decreasing?
Q2: Which loop has the greatest magnetic circulation?
Maxwell Eqns EM waves
Next week we will combine the Maxwell equations to
• Derive electromagnetic waves
• Derive the speed of light