PHY 2049: Physics II
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Tutoring Center is open in room NPB 1215,
M-F 12:00AM -4:00PM. It is free.
Exam II
25
20
15
10
5
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11
hitt
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A square loop of current-carrying wire with
edge length a is in the xy plane, the origin
being at its center. Along which of the
following lines can a charge move without
experiencing a magnetic force?
A. x = 0, y = a/2 B. x = a/2, y = a/2
C. x = a/2, y = 0 D. x = 0, y = 0,
E. x = 0, z = 0
Ch. 30 Induction and Inductance
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Magnetic Flux
Faraday’s Law of Induction
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Inductors
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Lenz’ law
Self and Mutual
Series RL circuits
Magnetic Energy
PHY 2049: Physics II
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Faraday’s Law:
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Electric generators
Electric guitars
Engine starters, cars, scooters etc.
Induction stoves
The basic idea: When a magnetic field changes in
time, it produces an electric field
PHY 2049: Physics II
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Some concepts:
 B   B.dA
Faraday’s law
V   E.dl
Lenz’ law:
the kickback
 B
V  
t
PHY 2049: Physics II
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Things that matter
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Pole
Direction of motion
PHY 2049: Physics II
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Seen From left
Switch turned on
Switch turned off
PHY 2049: Physics II
Self inductance
PHY 2049: Physics II
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Self inductance
NΦB = Li
Analogously mutual
inductance.
PHY 2049: Physics II
di
e  iR  L
dt
e
 Rt / L
i  1 e
R
  L/R


PHY 2049: Physics II
When the switch is first thrown
The inductors block any current. All
current flows through the middle
resistance. I = V/R
Later, the inductors are all closed and
the current is then I = 3V/R.
How much time does it take for the
current to rise?
PHY 2049: summary
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Faraday’s Law
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Lenz’ Law
the minus sign
Inductance self and mutual
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V = -dΦ/dt
V = L dI/dt
Time evolution of current
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Time constant t = L/R
Transformers