Week 8: 10/20/09 - 10/27/09
Environmental Physics    [You might attach this to the front of your homework.]
Ben Brabson

Readings for this week:
T Oct. 20        Ch. 8.1-8.7    (Cooke, Halgren, Steffen) + Electric energy & power
R Oct. 22       Ch 8.1-8.7      (Chadwick) + Electric Storage, Batteries, Fuel Cells
T Oct. 27       Ch. 9.1-9.6     Generation & Use of AC Power                 HW6 due
R Oct. 29                             (Regular classroom meeting at 3:35 pm, and leaving
                                       right after class for supper at Ben's House - Tel: 332-6507
                                       2000 Crandall Court in Hyde Park)

Homework #6: MH&C: 8.6, 8.7, 8.22 and the three special problems below.  Problem 8.22(b) requires the reformation of Hydrogen from CH4.  Let's assume that the reformation process is the catalytic process, CH4 + O2 --> CO2 + 2H2 that produces two moles of H2 for every mole of CH4.

           Special Problem #1: The mechanical power required at the rear wheels to drive a 2-ton car at constant speed of 40 mi/hr is approximately 9 kW.  Consider a typical automobile battery with the following characteristics [V = 12.0 volts, Capacity = 96 A h, Volume = 440 in2, Weight = 29 pounds, Cost = $70.00].  How many batteries would be needed to go 100 miles?  How much weight and volume?  If the energy for recharging a battery is purchased from the power company at 8 cents/kWh, what is the cost of going the 100 miles, and how does this compare with that of gasoline for an ordinary auto?
              Special Problem #2: It is often said that, since light bulbs use much more power just after being turned on, one should leave the lights on when leaving the room for less than 5 or 10 minutes.  There is some basis for this argument; a 100 W bulb has a resistance of about 144 ohms at its operating temperature but a resistance of only 16 ohms when it is cold, and it therefore does use more power just after being turned on.
    a.) How much power does a cold 100-W bulb use when connected to a 120 volt line?
    b.) A bulb takes about 0.1 second to reach its operating temperature.  Is it a good idea to leave the light on when you plan to be out of the room for 5 minutes?
               Special Problem #3: How much time is required to place a 25-mm chromium layer on a 4000-cm2 car bumper with a 250-A current? (The atomic weight of chromium is 52, its density is 7.2 g/cm3, and its valence is +2.) [Ans: 17 min 50 sec].

News & Events This Week:
1.) Physics - 4:00 pm, Wednesday, Oct. 21, 2009, SW119, Eric Adelberger, U. of Washington, A low-energy frontier of particle physics.
2.) Geography - 4:00 p.m. Friday, October 23, 2009, SB150, Sara Pryor, IUB, Climate Variability, predictability, and change in the Mdiwestern USA.
3.) Geology - 4:00 pm, Monday, Oct. 26, 2009, Geology, Mike Snow, IUB, What scientists learn when they slow down and scatter neutrons.