Chapter 10: part 2Ohms 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 headfor 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

SuperconductivityMajor problem with energy transfer: transmission losses ~10%High temperature superconductors; greatly reduce losses

High temperature superconductors-will conduct at temperaturesAchievable 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 willStay 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 producesMore 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 energySaving equipment with savings on energy cost.

Quote from Prizewinning Engineer

What will the lights of the future be?

L.E.D.sLight EmittingDiodes

Lumens per Watt

Lumens: measureOf light intensity

How do incandescentsMercury, halogensLow pressure sodiumFluorescents measureUp?

L.E.D.s How They Work

Semi-conductor

N-type layer-Supplies electrons

P-type layer:supplies positiveCharges or holes

In the active layerPhotons of lightEmitted.

Solar cells: also useSemi-conductorsN and P type layers

Lighting Whales with LEDsCan’t use visible light? Why?

Light is in near infra-red

Visible to videotape but not to whales

LEDS allow selection of wavelengthOf 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 CellsFuel cell: combines a fuel (Often natural gas or hydrogen)With oxygen. Uses the chemical Energy to produce electricity.

Present cost: $3000 to $4000 perKilowatt: too expensive

Greenhouse Gas Emissions

Why are zero emissionsVehicles (electric cars) Not necessarily the bestChoice?

Cost for Fuel Cells :Medium TermLife cycle costs: centsPer mile

Yellow: FuelPurple: ElectricityDark blue: MaintenanceBrown: Fuel StorageRed:BatteryLight blue: Fuel CellGreen:Basic Vehicle Cost

Long Term: Costs for Fuel CellsLife cycle costs: centsPer mile

Yellow: fuelPurple: electricityDark blue: MaintenanceBrown: Fuel StorageRed:BatteryLight blue: Fuel CellGreen: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 enginesDrawbacks: platinum catalyst in short supply

Fuel Cell: Central Park, New York

Fuel Cell Powered Bus

Fuel Cells: The FutureDaimler/Chrysler and General Motors: Fuel cell powered carBy 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 hydrogenFor 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.