Energy in Electrical Systems

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Energy in Electrical Systems

• 5.3

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• Capacitors
• A. Electrical device that stores energy in an
  electric field using a pair of parallel plates
• B. Potential difference source removes
  electrons from one plate and deposits them on the
  other plate
• C. Charge separation and the buildup of
  electric field and voltage continue until
  potential difference across the capacitor equals
  that of the power supply
• D. Two conductors separated by an insulator

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II. Capacitance A. Proportionality constant
between charge and potential difference (C) B.
Q C ?V C. Charge capacitance x potential
difference between plates D. Farad (F)
coulomb per volt (C/V) E. Most
capacitorsmicrofarads (µF) 10-6F or picofarads
(pF) 10-12F
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III. Potential Energy in Capacitors A. PE ½ C
?V2 B. Potential Energy Stored in a Capacitor
½ (capacitance) (potential difference)2 C. 1J
1F V2
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IV. Magnetic Fields and Induced EMF A.
Electric field creates a magnetic field B.
Concentric circles around a wire C. Two
wiresopposite fields attract, alike fields
repel D. Coil or solenoidseries of wire loops
to make a helix (see p. 267)
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E. Electromagnetic Induction 1. Electric
field can cause current to flow and therefore
produce a magnetic field. 2. If a loop of wire
moves through a magnetic field, current is
produced in the wire.
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F. Electromotive Force 1. Induced voltage in
a wire when a magnetic field moves past the wire
or if a wire moves past a magnetic field 2.
Increase by a. Using a larger magnet b.
Using a coil with a larger diameter c. Using
a coil with more turns of the wire d. Moving
the magnet faster
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3. Lenzs LawThe changing magnetic field
caused by the moving magnet induces a current,
and the direction of the induced current is such
that its own magnetic field opposes the changes
responsible for producing it.
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V. Inductors A. Electrical device that stores
energy in a magnetic field B. Solenoid or coil
of wire VI. Inductance A. Proportionality
constant (L) between the EMF and rate of change
of current B. EMF -L ?I / ?t C. Henry (H)
1 volt per ampere per second (1Vs/A)
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• VII. Potential Energy in Inductors
• A. PE ½ LI2
• B. Potential energy stored in an inductor ½
  (Inductance) (current)2
• C. 1 J 1 H A2
• Controlling Energy in Electrical Systems
• A. Filter circuitssmooth out voltage changes
  or current changes
• B. Electric motors are frequently equipped with
  capacitors or inductors to help the motors start.