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PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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Problem 32-7 The current in a coil changes from 3.50 A to 2.00 A in the same direction in 0.500 s.
If the average Emf induced in the coil is 12.0 mV, what is the inductance of the coil?
Self Inductance: The changing flux through the circuit and the resultant induced emf arise from the
circuit itself. Recall Faraday’s Law mf  
d B
and that  B  B  I , therefore the self-inducced
dt
emf is always proportional to the time rate of change of the current:
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I Ideal L ….with no resistance
PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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II Resistance is a measure of opposition to current
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1.
PHYS 2114
Capacitors are devices that produce a uniform electric field and therefore have the capacity to store
energy…potential energy. U = (CV2)/2
2.
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LECTURE 18
Instructor: Professor Donna Bandy
C depends on the geometry
Inductors are devices that produce a uniform magnetic field. The practical uses come when large
magnetic fields are necessary to the engineering system. L/l = on2A
L depends on the geometry;
N/l = n
Potential difference across inductor: Two important instances (a) and (b)
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PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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Inductors
:
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PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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Problem: A 1.0 A current passes through a 10 mH coil. What potential difference is induced across the coil if
the current drops to zero in 5 s?
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PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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Energy in Magnetic Fields
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PHYS 2114
LECTURE 18
Instructor: Professor Donna Bandy
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Typical Problem: Text 32.48 (Oscillations in an LC Circuit) A 1.05-H inductor is connected in series
with a variable capacitor in the tuning section of a short wave radio set. Calculate the capacitance that tunes
the circuit to a signal from the transmitter broadcasting at 6.30 MHz.
LC Oscillations Without resistance
Eight Stages in a Single Cycle of Oscillations
of LC Circuit without resistance.
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