Transcript Energy in Electrical Systems

Energy in Electrical
Systems
5.3
I. 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
II. Capacitance
A. Proportionality constant between charge
and potential difference (C)
B. Q = C ΔV
C. Charge = capacitance x potential
difference between plates
D. Farad (F) = coulomb per volt (C/V)
E. Most capacitors—microfarads (μF) 10-6F
or picofarads (pF) 10-12F
III. Potential Energy in Capacitors
A. PE = ½ C ΔV2
B. Potential Energy Stored in a Capacitor =
½ (capacitance) (potential difference)2
C. 1J = 1F · V2
IV. Magnetic Fields and Induced EMF
A. Electric field creates a magnetic field
B. Concentric circles around a wire
C. Two wires—opposite fields attract, alike
fields repel
D. Coil or solenoid—series of wire loops to
make a helix (see p. 267)
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.
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
3. Lenz’s Law—The 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.
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 · ΔI / Δt
C. Henry (H) = 1 volt per ampere per
second (1V·s/A)
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
VIII.Controlling Energy in Electrical Systems
A. Filter circuits—smooth out voltage
changes or current changes
B. Electric motors are frequently equipped
with capacitors or inductors to help the
motors start.