Transcript 5.3 Electrical Energy Notes

Chapter
5.3 Notes
Electrical Energy
A Capacitor is an electrical
device that stores energy in an
electric field.
Leyden Jar
Capacitor Demo
A power supply removes
electrons from one plate in
a capacitor and places them
on a second plate.
This causes the plate that
loses electrons to become
positively charged and the
plate that gains electrons to
become negatively charged.
The work done to create this
electric field is equal to the
potential energy stored in the
field.
• Equation for Work in
an electric field = ½
x charge x Voltage
•W=½qV
• If the charge is 10 and
the change in Voltage is
6, what is the work
done?
• W=½qxV
• W = .5 x 10 x 6
• W = 30 J
The charge on either
plate of a capacitor is
equal to the
Capacitance x voltage
Capacitors have fixed
values of capacitance.
The constant for a capacitor
is called capacitance and is
represented by the letter C.
Charge of a plate in a
capacitor = Capacitance x
voltage
q=CxV
• If the Capacitance is
.0005 and the Voltage is
200 V, what is the
charge?
• q=CxV
• q = .0005 C/V x 200 V
• q = .1 C
• Potential energy in
a capacitor = ½
(Capacitance)
2
(Voltage)
2
• PE = ½CV
• If the Capacitance is .0005
and the Voltage is 200 V,
what is the Potential Energy
stored?
2
• PE = ½CV
2
• PE = ½ (.0005)(200)
• PE = ½ (.0005)(40,000)
• PE = 10 J
If an electric charge is
moving, it will create a
magnetic field.
A magnetic field is a circle
with the current in the center:
Ferro Fluid Demo
If two currents
are in the same
direction, the
wires are
attracted.
If two currents
are in opposite
directions, the
wires are
Repulsed.
The Earth’s magnetic field is
caused by currents in the molten
iron core found at the center of
the earth.
The Earth’s Magnetic Field causes
the Northern Lights by attracting
electrically charged particles given
off by the sun.
A magnetic field can also
create an electric field. This
is called electromagnetic
induction (EMF).
If a loop of
wires move
through a
magnetic
field, a
current is
produced in
the wire.
Demonstration
To increase the electricity
created by a magnetic field:
Use a larger magnet
Use a coil (wire) with a
larger diameter
Use more turns of the wire
Move the magnet faster
A capacitor stores energy in an
electric field and an inductor is
an electrical device that stores
energy in a magnetic field.
The amount of energy that an
inductor can hold is called
inductance.
Use the symbol L to represent
Inductance.
Equation for EMF = inductance (current/time)
EMF = -L (I/t)
• A coil with an inductance of
.0045 Hertz a current of 1000
amps in 2 seconds. What is
the EMF?
• EMF = -L (I/t)
• EMF = -.0045 (1000/2)
• EMF = -.0045 (500)
• EMF = -2.25 V
• Potential energy in
inductors (Equation)
= ½ inductance
2
(current)
2
• PE = ½ LI
• A coil with an inductance of
8 Hertz and a current of 15
A has how much PE stored?
2
• PE = ½ LI
2
• PE = ½ (8) 15
• PE = ½ (8)(225)
• PE = 900 J