Download Lecture14_Electricity

ELECTRICITY
Electricity per person per year = 22 trillion kWh / 7 billion =
3000 kWh
(United States = 14,000 kWh)
Originally, Electric Utilities  Vertically Integrated
Regional monopolies, highly regulated
This ended in 1978 with PURPA (Public Utility Regulatory
Policies Act)
 Divided energy industry into Generation, Transmission, and
Distribution
 Opened the door to independent power producers
Originally, Electric Utilities  Vertically Integrated
Regional monopolies, highly regulated
This ended in 1978 with PURPA (Public Utility Regulatory
Policies Act)
 Divided energy industry into Generation, Transmission, and
Distribution
 Opened the door to independent power producers
Many states encourage transition to renewable energy
sources through Renewable Energy Portfolio Standards
(RPS)  Example: 10-20% of energy must come from
renewable sources by a certain date
What is electricity?
What is electricity?
Flow of electrons
Atomic Models
Atomic Models
What are the 4 forces of
the universe?
Gravity
Strong Nuclear Force
Weak Nuclear Force
Electromagnetism
Suppose I push against the wall…..what force am I using?
Suppose I push against the wall…..what force am I using?
Electromagnetism
Suppose I push against the wall…..what force am I using?
Electromagnetism
Can I ever actually touch the wall?
Suppose I push against the wall…..what force am I using?
Electromagnetism
Can I ever actually touch the wall?
No!
How does a flashlight work?
How does an electrical circuit work?
How does an electric car work?
How does an electric car work?
What is the current in the circuit?
What is the current in the circuit?
V = I R (Voltage = Current x Resistance)
 I = 8 amps
Appliances in Series:
If V = 120 volts and
R1 and R2 are both 5
ohm, what is the
current in the circuit?
Appliances in Series:
If V = 120 volts and
R1 and R2 are both 5
ohm, what is the
current in the circuit?
V=IR
120 = I x 10
 I = 12 amps
Appliances in Series:
If V = 120 volts and
R1 and R2 are both 5
ohm, what is the
current in the circuit?
V=IR
120 = I x 10
 I = 12 amps
What happens to the
voltage around the
circuit?
Appliances in Series:
If V = 120 volts and
R1 and R2 are both 5
ohm, what is the
current in the circuit?
V=IR
120 = I x 10
 I = 12 amps
What happens to the
voltage around the
circuit?
It drops in stages
Gullfoss, Iceland
Appliances in Series:
What happens to the
current if you keep
adding resistors?
Appliances in Series:
What happens to the
current if you keep
adding resistors?
V=IR
120 = I x (5+5+5+5)
 I = 6 amps
The current drops
Appliances in Parallel:
If V = 120 volts and R1
and R2 are both 5
ohm, what is the
current in the circuit?
Niagara Falls
Appliances in Parallel:
If V = 120 volts and R1
and R2 are both 5
ohm, what is the
current in the circuit?
1 / Rtot = 1/5 + 1/5
1/Rtot = 2/5
Rtot = 2.5
V=IR
120 = I x 2.5
 I = 48 amps
Appliances in Parallel:
If V = 120 volts and R1
and R2 are both 5
ohm, what is the
current in the circuit?
1 / Rtot = 1/5 + 1/5
1/Rtot = 2/5
Rtot = 2.5
V=IR
120 = I x 2.5
 I = 48 amps
What happens to the
voltage across them?
Appliances in Parallel:
If V = 120 volts and R1
and R2 are both 5
ohm, what is the
current in the circuit?
1 / Rtot = 1/5 + 1/5
1/Rtot = 2/5
Rtot = 2.5
V=IR
120 = I x 2.5
 I = 48 amps
What happens to the
voltage across them?
It is the same = 120 V
Appliances in Parallel:
What happens to the current
if you keep adding
resistors?
Appliances in Parallel:
What happens to the current
if you keep adding
resistors?
1 / Rtot = 1/5+1/5+1/5+1/5
1/Rtot = 4/5
Rtot = 1.25
V=IR
120 = I x 1.25
 I = 96 amps
It increases
Why do you want Christmas lights to be in parallel, not series?
Why do you want Christmas lights to be in parallel, not series?
Because if one bulb fails, the whole circuit doesn’t stop
Why do you want Christmas lights to be in parallel, not series?
Because if one bulb fails, the whole circuit doesn’t stop
Why might this still be a problem?
Why do you want Christmas lights to be in parallel, not series?
Because if one bulb fails, the whole circuit doesn’t stop
Why might this still be a problem?
Power delivered = volts x current
P = VI
P = (IR)I
P = I 2R
The power increases with the square of the current, and current
is greater for parallel circuits  you are more likely to blow a
fuse.
Appliances in Parallel:
Table 10-2a, p. 340
An Electric Current in a wire generates a magnetic field
rotating around it!
An Electric Current in a wire generates a magnetic field
rotating around it!
 The “right-hand rule” gives the direction
A Solenoid
A Solenoid and Bar Magnet have the same magnetic field!
Cylindrical convection in the outer core creates the
geomagnetic field
https://www.youtube.com/watch?v=XU8nMKkzbT8
The opposite works too!!! If you move a magnet through a coil of
wire, you create an electric current in the wire!!
 Electricity Generator (you just need a way to move the magnet)
 https://www.youtube.com/watch?v=CQSIdbY4XTU
Hydroelectric Turbines  use water to turn the the coils of wire
through a magnetic field
Electricity is
transmitted over
high voltage lines
A Transformer: Converts a current at one voltage into a current in
a separate circuit at a different voltage
 Entirely depends on the relative numbers of coils
A Transformer: Converts a current at one voltage into a current in
a separate circuit at a different voltage
 Entirely depends on the relative numbers of coils
Remember….power is proportional to the square of the current:
P = I2R
The power lines have a small resistance, and so the power lost to
heat will be P = I2R
 Need to reduce the current to reduce power lost!
For the Transformer, V(in) x I(in) = V(out) x I(out)
If you go from 120 V to 120,000 V, your current is 1000 times less,
and your power loss is a million times less!!