WELCOME TO HELP SESSION 3: ALTERNATIVE FORMS OF ENERGY

Transcription

1 WELCOME TO HELP SESSION 3: ALTERNATIVE FORMS OF ENERGY The final exam is Mon, Apr 29, at 6:00 pm (same room as your midterm exams) Review sessions: Thurs, 4/25, 7:00 pm and Fri, 4/26, 1:00 pm in 2005 Smith. Drop in: Mon, Apr 29, 2:00 5:30 in 2005 Smith Be sure to bring a calculator to the exam!

2 Alternate Forms of Energy Solar energy (electromagnetic radiation from the Sun) Water energy (including tidal and geothermal) Wind energy Biomass energy

3 Radiant energy (electromagnetic radiation) Radiant energy results from vibrations of charges. As the charges vibrate, they produce waves of energy. Waves of electromagnetic radiation travel at a speed of 3 x 10 8 (300,000,000) meters/second in a vacuum.

4 Wavelength, period, and frequency The wave s period is the time it takes to complete one cycle. The wave s frequency is how often it completes a cycle. Wave Length Wave Length Distance Wave Period Wave Period Time Lower frequency Higher frequency

5 Wave speed and frequency s = f L s = speed at which radiant energy travels (meters/sec or mi/sec) f = frequency (cycles/sec, or Hertz) L = wavelength (in meters, miles, or feet) frequency = 1/period Frequency is measured in Hertz (Hz) 1 Hz = 1 cycle/second

6 Fusion in stars: the proton-proton chain Stars smaller than 1.2 times the mass of the Sun use a hydrogen-burning proton-proton chain as their primary fusion process. 1) two hydrogen nuclei (protons) fuse to form a nucleus of deuterium. 1 H + 1 H 2 H + e + + n e (+1.44 MeV) 2) Deuterium fuses with another hydrogen to form an isotope of helium called tritium. 2 H + 1 H 3 He + g ( MeV) 3) Two tritium fuse to form a stable helium nucleus plus two hydrogen nuclei. 3 He + 3 He 4 He + 1 H + 1 H ( MeV)

7 Fusion Combining of nucleons or small nuclei Exothermic Fission Breaking apart of large nuclei Exothermic Total number of nucleons

8 Energy in the early universe The Universe began with an explosion: The Big Bang. As the Universe expanded and cooled, increasingly complicated structures formed. The energy per photon can be found from the temperature: with E = 3 k T E = energy (in joules or electron volts ev) k = Boltzman s constant = 1.38 x J/K or 8.62 x 10 5 ev/k T = temperature (in kelvin)

9 Hubble s constant Hubble s Law: The speed of a galaxy increases in direct proportion to its distance from an observer. The recessional velocity of an object is the rate at which it appears to be moving away. The Hubble constant (H o ) is the slope of the graph of velocity of galaxies vs. their distance. The inverse of the Hubble constant, (1/H o ) gives an estimate of the age of the Universe.

10 Formation of chemical elements Most of the hydrogen, helium and lithium in the Universe was created during the Big Bang. Carbon is formed when two alpha particles fuse to form an unstable isotope of beryllium. 4 He + 4 He 8 Be ( 0.1 MeV) If a 3 rd alpha is added before the beryllium nucleus decays back into two alphas, carbon is formed. 8 Be + 4 He 12 C (+ 7.4 MeV)

11 Formation of heavy elements Elements through iron are formed when stars more massive than 5 times the mass of the Sun collapse violently. Increasingly massive elements are fused until iron is produced. Elements heavier than iron are formed when large stars collapse one last time and explode violently in a type II supernova. Enough energy is released to begin endothermic fusion reactions of heavy elements. These reactions require both activation energy and energy to produce the endothermic reaction.

12 Doppler effect A stationery light source emits waves of light uniformly in all directions. If the same light source moves to the right, the wavelengths are no longer evenly spaced. Light from a receding source has longer wavelengths, and the light is shifted to the red end of the spectrum. The redshift of distance stars shows they are moving away from the Earth. Spread of waves over time

13 Hertzsprung-Russell diagram of stars

14 Source:

15 Focusing radiant energy Light reflected from concave and convex mirrors. Focus A Concave Mirror Focuses Radiant Energy A Convex Mirror Spreads Radiant Energy

16 Focusing radiant energy Light passes through concave and convex lenses. Focus A Concave Lens Spreads Radiant Energy A Convex Lens Focuses Radiant Energy

17 Orientation of a solar collector In the northern hemisphere, solar collectors face south. In winter, the collector angle equals the latitude + 15 o. In summer, the collector angle equals the latitude - 10 o. 15 o 40 o Columbus, OH in winter 10 o Columbus, OH in summer

18 Features of a solar house Deciduous trees or a roof overhang on the south side of a house to shade windows from the direct sun in the summer, but allow the sun to shine in through windows in the winter when the sun is lower. Embankments and non-deciduous trees on the north side of the house to block winter winds. A thermal mass may be used to store solar energy gathered during the day for use at night when the temperature drops. Rooftop solar collectors to supplement the heating system and to generate electricity. Fiber optic light pipes to bring outside light into the interior of the house. Insulation of walls and attic to reduce heat transfer. Vents to exhaust hot air from the house.

19 Solar cells Solar cells use the photoelectric effect to produce electricity. When electrons in the cell absorb photons of radiant energy, some electrons have enough energy to escape from their atom and form an electric current. Light Rays + Output Voltage _

20 Photon Time 1: A photon is absorbed by an electron. Time 2: The electron escapes from the atom. When an electron in a solar cell absorbs a photon with sufficient energy, the electron can escape from the atom s electron cloud. These unbound electrons form an electric current.

21 Visible light spectrum Source:

22 Energy of a photon The energy of a photon is related to the frequency and wavelength. E = h f = (h c)/l E = energy of a photon (joules) h = is a constant = 6.63 x joule sec f = frequency (Hertz) c = speed of radiant energy = 3 x 10 8 m/s L = wavelength (meters).

23 Power from a solar cell The power generated by a solar cell depends on the amount of solar insolation striking the cell the size (area) of the cell the efficiency of the solar cell where P = I x A x Eff P = power (in watts) I = solar insolation ( in watts/meter 2 ) A = area of collector (in meters 2 ) Eff = the efficiency of the solar cell

24 Source:

25 The Earth s water cycle Water from oceans, lakes, rivers, and the soil evaporates when radiation from Sun warms the Earth s surface. Water vapor rises, is cooled, and condenses on dust particles, forming clouds. When clouds become saturated, precipitation falls as rain or snow. Precipitation eventually runs back into lakes and oceans and the cycle repeats. Latent heat of vaporization is removed from the atmosphere when water evaporates and is added when water vapor condenses. Solar energy drives the water cycle.

26 Energy from ocean tides The moon s gravitational force causes the oceans to form two bulges, one on each side of the Earth. As the Earth spins on its axis, land bordering the oceans passes through both bulges each day. This produces two high tides and two low tides per day. The gravitational attraction between the Earth and the moon causes the water on the side facing the moon to be pulled toward the moon. On the opposite side of the Earth, water tries to continue moving away from the Earth, forming a bulge. Tide_overview.svg

27 Tidal generators

28 Electricity from geothermal energy Heat in the Earth s core is the result of radioactive decay. Thermal energy is conducted from the core through the Earth s mantle. This thermal energy can produce the steam needed to turn generator turbines This type of geothermal energy is available only in geologically unstable areas, such as volcanically active Iceland. _Faithfull-pdPhoto.jpg

29 Consequences of melting glaciers Mountain glaciers will disappear, many before Billions of people depend on glacial melt water. Consequences: Glacial melt water is the primary source of the water used to generate hydropower. Other energy sources will be needed to replace this hydropower. Much irrigation water comes from lakes that are replenished by glacial melt water. Other sources of drinking water will be needed. Many glacial lake dams could fail, flooding valleys.

30 Energy from wind Wind pattern due to convection of warm air from the equator to the high latitudes. Wind pattern due to convection AND the Coriolis force of the rotating Earth. 5currents1.html

31 Daytime: Warm air rises above the land. Cool air over the water flows toward the land. Night: Warm air rises above the water. Cool air over the land flows toward the water.

32 Wind turbines The moving blades turn a shaft connected to a generator. This motion spins magnets near coils of wire. Best locations: shorelines flat plains, and mountain ridges. Advantages: A renewable resource, no atmosphere pollution Blades are fatal to birds, bats, and insects. 250 feet Objections to the noise of the spinning blades and appearance of the large towers. s/1/14/wind_turbine_holderness.jpg&imgref

33 Fuel from biomass Biomass: plant material or animal waste used as a fuel. Bioethanol is ethyl alcohol that is distilled from plant material, such as corn, sugar cane or switchgrass. Biodiesel is produced from vegetable oils and animal fats, such as used cooking oil. Adding ethanol to gasoline reduces the amount of fossil fuel needed. Alcohol combustion may produce less soot than oil. The CO 2 released by the burning biofuel is equal to the uptake of CO 2 from the atmosphere by the plants that produced the biofuel. Thus, biofuel is considered carbon neutral.

34 Carbon cycle Carbon_cycle.jpg&imgref

35 The carbon budget The carbon budget is the balance of the carbon exchanges between carbon sinks and sources. A carbon sink is a component of the carbon cycle that absorbs and stores more carbon than it releases. A carbon source emits more carbon than it absorbs. The oceans are the largest active carbon sink on the planet. Human influence on the carbon budget 1) combustion of fossil fuel 2) deforestation 3) acid rain has makes sea water more acidic 4) the manufacture of concrete

36 Energy Advantages Disadvantages Fossil Plentiful (at least for now) and inexpensive greenhouse gases, acid rain, soot. Non-renewable Biomass Wind Tidal plentiful, inexpensive, renewable Inexpensive to operate, renewable Renewable. No atmospheric pollution Renewable. No atmospheric pollution Soot. (No net carbon dioxide is released.) Expensive to install, noisy, affects scenic vistas, can harm birds Limited locations. Can change aquatic ecosystem Dams can change the aquatic ecosystem Nuclear Hydroelectric Geothermal Solar No atmospheric pollution Thermal pollution. Possible nuclear accidents. Storage of radioactive waste. Limited atmospheric pollution. No atmospheric pollution. Renewable Large quantities available only in areas with hot rock close to the surface. Low efficiency, expensive, not always available.

37 Heat flow energy transferred time OR E t E t K A ( Thot Tcold ) L A ( T hot Tcold ) R K = the thermal conductivity (J/s m o C or BTU inch/hour foot 2 o F) A = the cross sectional area (meters 2 or feet 2 ) T = temperature ( o C or o F) L = thickness (meters or inches) R = insulation value = L/K T hot Heat flow L Area T cold

38 The cost of using electricity Electric companies charge for electricity in units of kilowatt hours (kwh). One kilowatt hour = 1,000 watts of power provided for one hour. To find the number of kilowatt hours, 1) divide watts by 1,000 to find kilowatts 2) multiply kilowatt by the number of hours of use. To find the cost of using electricity, multiply the kilowatt hours by the cost per kilowatt-hour

39 Payback time How long it takes to recover the cost of purchasing a more expensive appliance from the savings in energy. The total cost of using an appliance is the purchase price plus the cost of operation: Total cost = purchase price + (cost/year x # of years) An energy-efficient dishwasher costs $80 more than a less efficient dishwasher. The energy-efficient dishwasher saves $20 each year in operating costs. What is the payback time for the dishwasher? additional cost = $80 x 1 year = 4 years savings each year $20

40 FOR THE FINAL EXAM The final exam is Mon, Apr 29, at 6:00 pm (same room as your midterm exams) Review sessions: Thurs, 4/25, 7:00 pm and Fri, 4/26, 1:00 pm in 2005 Smith. Drop in: Mon, Apr 29, 2:00 5:30 in 2005 Smith Be sure to bring a calculator to the exam!