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 = I 2 * 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 layer- Supplies 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 Honda: Fuel cell powered car by 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.