Transcript 17.9 Storage of Electric Energy

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17.7 Capacitance
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Ratio of the charge on a
conductor to the potential
difference between the
conductors.
Q
C
V
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Units of farads (F)
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Usually in μF or pF (10-12 F)
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17.7 Capacitance

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A
For a parallel-plate capacitor: C   o
d
Applications: cameras, computers, TVs, noise filters,
starter motors, etc.
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17.8 Dielectrics
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An insulating material placed between
plates of a capacitor that increases the
capacitance: C = κCo
The polarization of the dielectric will
cause an decrease in the electric field.
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Application: measure humidity in air
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17.9 Storage of Electric Energy
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Work done to move Δq through V is ΔW= VΔq
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PE stored = ½QV = ½CV2 = Q2/2C
The energy is stored in the electric field between the
plates with a density of ½ εoE2.
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Total work = ½QV
Defibrillators
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17.9 Storage of Electric Energy
1) Battery Compartment
10
2) Capacitor
3
7
3) Transformer
4) Capacitor
11
5) Diode
1
4
6
6) Transformer
7) Neon Indicator Light
8
8) Capacitor
9
9) Resistor
2
10) Flash Tube
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11) Transistors
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17.11 The Electrocardiogram
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Cell area ~ 105 m2
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Charge per surface ~ 10-8 C
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Depolarization
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17.11 The Electrocardiogram
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