Chapter 10: part 2
Ohms Law
Superconductivity
Parallel and Series Circuits
Delivery of Power in a Circuit
Pricing Energy
Fuel Cells
Energy in the News
Ohm’s Law
V=I*R
V= voltage, units of volts
I= current, units of amperes
(coulombs per second)
R =resistance, units of ohms
Physical Meaning
Resistance: resistance to flow of electrons
(pipe: wire)
Voltage: electrical potential ( like pressure head
for a pump driving flow= potential energy per unit charge)
1 volt = 1 Joule per coulomb
Current: quantity of electrons flowing
Toaster
What is the current?
Resistive Heating
Power = Voltage * Current
P= V*I
Plug in ohms law, V= I* R
P = I2 * R
Electric stoves, toasters and hair dryers: What do
they have in common? Expected wattage?
Electrical Energy: Work or Heat
Superconductivity
Major problem with energy transfer: transmission losses ~10%
High temperature superconductors; greatly reduce losses
High temperature superconductors-will conduct at temperatures
Achievable with liquid nitrogen (still pretty cold!!)
Ceramics: latest superconductors. Normally insulators.
Structure of ceramics: like high pressure silicates (Walker)
High pressure pressure at LDEO.
Simple Circuits
Parallel: everything connected by the same circle of
Wire
Series: a set of interconnected circular circuits
Meissner Effect
Superconducting materials exclude magnetic fields
Therefore, a magnet near a superconductor will
Stay in the air
Result: magnetic levitation (MAGLEV)
Bullet trains in Japan and Germany use MAGLEV
Series and Parallel Circuits
Parallel circuits:
Resistances add
Series circuits:
Currents add
Household circuits:
Which type?
Fire danger?
How to reduce fire hazard?
Batteries: Series and Parallel
Which arrangement produces
More voltage?
More current?
More resistance?
More power?
Typical Household Circuit
What should be included to ensure safety?
Prices of Energy
Typical prices of energy per kilowatt hour?
Locally (on Long Island)?
Nationally?
Rates for wind power?
Payback Time on Energy Efficiency
Energy efficiency is an investment
Example; compact fluorescent bulbs
Cost; $10 each (10 times as much), last 10 times as long
Use 1/4 the energy of incandescent bulbs.
Payback time=time to pay back the extra cost for energy
Saving equipment with savings on energy cost.
Quote from Prizewinning Engineer
What will the lights of the future be?
L.E.D.s
Light Emitting
Diodes
Lumens per Watt
Lumens: measure
Of light intensity
How do incandescents
Mercury, halogens
Low pressure sodium
Fluorescents measure
Up?
L.E.D.s How They Work
Semi-conductor
N-type layerSupplies electrons
P-type layer:
supplies positive
Charges or holes
In the active layer
Photons of light
Emitted.
Solar cells: also use
Semi-conductors
N and P type layers
Lighting Whales with LEDs
Can’t use visible light? Why?
Light is in near infra-red
Visible to videotape but not to whales
LEDS allow selection of wavelength
Of light.
LEDS work well at high pressures
1 atmosphere per 10 meters of water
Common Uses of LEDs
Upper left; SGT
Pepper costumes
Upper Right;
Traffic light
Lower Right;
Taillights, turn
signals
Lower left: signs
Fuel Cells
Fuel cell: combines a fuel (
Often natural gas or hydrogen)
With oxygen. Uses the chemical
Energy to produce electricity.
Present cost: $3000 to $4000 per
Kilowatt: too expensive
Greenhouse Gas Emissions
Why are zero emissions
Vehicles (electric cars)
Not necessarily the best
Choice?
Cost for Fuel Cells :Medium Term
Life cycle costs: cents
Per mile
Yellow: Fuel
Purple: Electricity
Dark blue: Maintenance
Brown: Fuel Storage
Red:Battery
Light blue: Fuel Cell
Green:Basic Vehicle Cost
Long Term: Costs for Fuel Cells
Life cycle costs: cents
Per mile
Yellow: fuel
Purple: electricity
Dark blue: Maintenance
Brown: Fuel Storage
Red:Battery
Light blue: Fuel Cell
Green:Basic Vehicle Cost
Types of Fuel Cells
PEM: Proton exchange membrane
Fuel cell cars: can be refueled in minutes (unlike ZEVs)
Range similar if natural gas or methanol powered, Very Quiet!!
Use 2/5 of energy of typical cars with internal combustion engines
Drawbacks: platinum catalyst in short supply
Fuel Cell: Central Park, New York
Fuel Cell Powered Bus
Fuel Cells: The Future
Daimler/Chrysler and General Motors: Fuel cell powered car
By 2004.
Honda: Fuel cell powered car by 2003.
Roughly 2.5 to 3 times as efficient as typical gasoline powered cars.
Wind farms on 6% of land in Great Plains: enough to produce hydrogen
For all USA cars and light trucks if all fuel cell powered!!
Photovoltaic cells (solar cells) on 1% of US land needed to provide
hydrogen for US Fuel cell fleet.