PH 102

Activities

Winter 2009-2010

1. Monday, Nov. 16 --  class list, syllabus, labs
Macroscopic and microscopic approaches to thermodynamics
Zeroth law of thermodynamics
Various thermometers - metal rod, liquid in open container, liquid in closed container, wire or thermister
Temperature scales - Fahrenheit, Celsius, Kelvin - and conversions between them
Triple point of water - 273.16 K at a vapor pressure of 4.58 torr
Thermal expansion of solids in one and two dimensions
Problem 13.18: Calculate the change of area of a rectangular plate when it is heated and its temperature increases by
ΔT.
Bimetallic strips, Demos: steel/brass strip heated in a flame;  ball and ring
2. Wednesday, Nov. 18
  Thermal expansion of solids in three dimensions - equation for the change of volume.  Table 13-1 on p. 358.
Video 1 - "Thermal Expansion:  Liquids", Video 2 - "Phase Change Expansion:  Ice Bomb"
Video 3 - "Thermal Expansion:  Breaking Rod", Video 4 - "Linear Expansion:  Determination of Alpha"
Ideal gases - Boyle's law, Gay-Lussac's law, Charles' law      Periodic Table
Animation-1 and Animation-2 illustrate these laws
Ideal gas law (Equation of State of an Ideal Gas)
Universal gas constant:  R = 8.314 J/mol-K = 0.08206 liter-atm/mol-K
Avogadro's number:  NA = 6.022 x 1023 molecules/mol
Boltzmann's constant:  k = R/NA = 1.38 x 10-23 J/K
Kinetic Theory of Gases, rms (root mean square) velocity, ave. KE per mole, ave. KE per molecule
3. Friday, Nov. 20
  Speed distribution of molecules in a gas - physlet - After it comes up and runs for awhile, click on "Average" and watch the graph evolve.
Graph of distribution of velocities in a gas (Nv vs. v).  Shows vrms, vave and vp (most probable).
Video 5 - "Kinetic Model: Temperature Effects on Gases", Video 6 - "Cryogenics: Organic Materials"
Review (Jacques) Charles law ...
Demo - cool things with liquid nitrogen: balloon, banana, plant leaves, ...
Video 7 - "Induced Phase Change: Solid N2"
Evaporation... Maxwell velocity distribution, demo - glass of water, explanation via the graph...
Relative humidity and vapor pressure
Video 8 - "Cryophorous: Cooling by Evaporation", Video 9 - "Induced Phase Change: Boiling by Cooling"
Video 10 - "Condensation: Formation of a Cloud"
Saturated vapor pressure (SVP), relative humidity (RH), partial pressure (PP), RH = 100*PP/SVP
Demo - humidity gauge
Fog, smog, vog (volcanic gas + fog) - CO2 and sulfur
Problems from Chapter 13.        Table 13-3
4. Monday, Nov. 23 - Chapter 14 - Heat - Q4
  Definitions:  calorie, kilocalorie (= food Calorie), Btu
Conversions:  1 kcal = 4186 J,  1 Btu = 252 cal
Mechanical equivalent of heat = J = 4.186 J/cal = W/Q  (Joule's law)
      heat absorbed = Q = m c ΔT,   where m = mass, c = specific heat,   ΔT = temperature change,  Table 14-1, p. 387
      heat gained = heat lost           (conservation of energy)
      latent heat of fusion of water = LF = 79.7 cal/g (at 0oC)
      latent heat of vaporization of water = LV = 539 cal/g (at 100oC)
If a substance changes phase:   heat gained (or lost) = mass x latent heat,  Q = m L
Problem:  Drop ice cubes into some water.  Calculate the final temperature.
      heat of combustion = heat given off in burning
      heat conduction - heat transfer occurs by molecular collisions with no net movement of the molecules
      rate of heat flow = H = Q/Δt = k A ΔT /
l    where k = thermal conductivity, A = area, l = thickness, Table 14-4, p. 396
Demo - touch metal, then an insulator (like wood) at the same temperature - which feels colder?
Video 11 - "Thermal Conduction:  Propagation in a Metal Rod", Video 12 - "Thermal Conductivity:  A Two Rod Combination"
5. Wednesday, Nov. 25 - Q5
  R-value = R = l / k,   rate of heat flow = H = Q / Δt = A ΔT / R,     Table 14-5, p. 397
Review - various forms of energy ... (10 listed in class)
Demo - happy ball, sad ball, energy conservation; push book along the table
Heat is another form of energy:  Q = mcΔTQ = mL
Three types of heat transfer:  conduction, convection, radiation
Convection:  when "hot" molecules are physically transported from one region to another. Convection may be natural - caused by variations of fluid density in a gravity field, or forced - caused by a fan.
Rate of heat flow = Q / Δt = h A ΔT
Wind chill temperature index - chart (National Weather Service)
Demo - Bunsen burner shadow... variation of air density
Video 13 - "Thermal Convection:  Induced Fluid Flow", Video 14 - "Thermal Convection:  Projection of Currents".
Radiation - heat is transferred from one molecule to another by electromagnetic waves.
Thermograms - Fig. 14-14, p. 402,  human bodies
Video 15 - "Thermal Radiation:  Transmission Using Parabolic Mirrors", Video 16 - "Thermal Radiation:  Black Body Effects", Video 17 - "Thermal Radiation:  Leslie's Cube".
Problem 14-44 on page 406.
6. Monday, Nov. 30 - Chapter 15.  The Laws of Thermodynamics
  The 1st Law:  All the heat (energy) added to a closed system (constant mass) can be accounted for as mechanical work, an increase in internal energy, or both.  In equation form: ΔU = Q - W
Various processes:  isothermal, isometric, isobaric, adiabatic
Internal energy of an ideal gas:  U = 3/2 nRT
Work = area under the PV curve
For an adiabatic process,
PV γ = constant
Video 18 - "Pressure and Temperature:  Piston in a Cylinder".
Human metabolism - conversion of internal energy (food - chemical energy) by an organism into other forms of energy:
     work, heat, waste products - metabolic rate (Table 15-5 on p. 415) varies like mass3/4
7. Wednesday, Dec. 2 - Q7
  Heat engines - a device for obtaining mechanical work out of the heat energy of fuel - 2-stroke engine (lawn mower, ...)
4 stroke gasoline engine (internal combustion) - Figure 15-13, p. 417
Two-cylinder four stroke motor
Flash Physics Animations:  2 stroke engine, 4 stroke engine
2nd Law of Thermodynamics
   Kelvin statement:  It is impossible to construct an engine that, working in a cycle, has no effect other than the
                              extraction of heat from a reservoir and the performance of an equal amount of work.
   Clausius statement:  It is impossible to construct an engine that, working in a cycle, has no effect other than the
                                  transfer of heat from a colder to a hotter body.
Coefficient of performance
Entropy
Problems from Chapter 14.
8. Friday, Dec. 4
 

Review:  1st Law of Thermo, ΔU = Q - W,  Drawings for a Real Heat Engine and a Real Refrigerator
2nd Law of Thermodynamics, Boltzmann's definition: S = k ln D, D = disorder parameter ΔS
0 for an isolated  system, ΔS = Q/T
Carnot Cycle - proposed by Sadi Carnot in 1824 - its a reversible heat engine with two adiabatic
                      and two isothermal processes, efficiency = e = W/QH = 1 - TL/TH.
Example:  Hot cup of coffee, find ΔS.   Video 19 - "Entropy - Mixing of a Dye"
Problems from Chapter 15.

9. Wednesday, Dec. 9 - Chapter 16 - Electric Charge and Electric Field
  Video 20 - "Electrostatics - Interaction of Charge", Video 21 - "Distribution of Charge on a Conductor",
Video 22 - "Induction of Charge".
Design and operation of an electroscope.
Nine basic experimental results:

1.  Electric charges are of two kinds, positive and negative.
2.  Like charges repel each other and unlike charges attract each other.
3.  Substances differ in electrical conductivity:  (a) conductors - have many "free" electrons,
     (b) insulators - have very few free electrons, (c) semiconductors - have some free electrons.
4.  The surplus charge on a solid or hollow conductor resides entirely on its exterior surface.
5.  Electric charge concentrates at edges and pointed surfaces on a conductor.
6.  When charges are separated by contact (rubbing things together), equal amounts of positive and negative
     charge are produced.  This is the Law of Conservation of Charge.  (Charge can be moved around but it cannot
     be created or destroyed.)
7.  Electric forces act at a distance.
8.  A body can be charged by conduction or induction.
9.  Higher humidity increases charge "leakage".

Demos:  (a) charged cassette case picks up shredded paper, (b) charge an electroscope by conduction and later by induction using various items - glass rod (+) and silk (-), PVC (-) and fur (+), (c) a charged balloon (rubbed on fur) "hangs" on a wooden door - and maybe other things, (d) a charged rod is brought near a falling thin stream of water - and deflects it - via induction.
10. Friday, Dec. 11 - Q10
  The Triboelectric Series - shows how strongly various materials hang on to their electrons when you rub them together.
List of items from Wednesday plus a few others, in order from most positive to most negative:
     1.  animal fur (+)
     2.  glass rod (+)
     3.  acrylic (+)
     4.  nylon (+)
     5.  wool (+)
     6.  silk (+)
     7.  paper
     8.  cotton
     9.  wood
    10. steel
    11. amber (-)
    12. rubber rod (-)
    13. brass, silver (-)
    14. polyester
    15. styrene (Styrofoam)
    16. saran wrap
    17. polyurethane
    18. polyethylene (like scotch tape)
    19. polypropylene
    20. vinyl (PVC)
    21. silicon
    22. Teflon (very negative)
Coulomb's Law - what you use to calculate the force between pairs of charges.
Superposition Principle - For multiple charges, the vector force on each one is the sum of the vector forces
                                    from all the others.
Charge and mass of the (1) electron, (2) neutron, and (3) proton
Analogy:  force between masses - force between charges
Definition of an electric field, E  =  Fe q  = k Q/r2
Technique for tracing electric field lines
Result: electric field lines always originate on positive charges and end on negative charges.  Fig. 16-30Fig. 16-31
Computer drawings - EM Field program - 3D sources - electric field vectors (E) and electric field lines
11. Monday, Dec. 14 - Went over Test 1
 

Video 23 - "Corona Discharge - Electronic Precipitator", Video 24 -  "Electric Fields:  Mapping of Force Fields"
Video 25 - "Electrostatics:  Force Exerted between Charges"
Applications of Electrostatics - How Photocopiers Work - Fig. 16-46How Laser Printers Work - Fig. 16-47
Chapter 17.  Electric Potential - Picture of Lightning on p. 470.
Telescope with Lightning - Kitt Peak telescope in Arizona - Picture hanging in the lobby of the John Deere Planetarium.
Night lightning on Jupiter - cloud tops illuminated by sunlight reflected from the moon Io - photos taken by the spacecraft Galileo in October, 1997.
Video 26 - "Corona Discharge:  Lightning Model" -  Lightning
Van de Graaff generator  -  transparency  --  demo: stack of aluminum plates, etc., volunteer

12.

Wednesday, Dec. 16
  Potential difference - gravitational and electrical
Electric potential difference, ΔV
The "ground symbol", definition of voltage:  potential difference with respect to ground.
Over short distances, points connected by a (metal) wire are at the same potential (ΔV = 0).
All points on the outside surface of a conductor are at the same potential.
An equipotential surface is one for which all points are at the same potential.
Around a point charge q, the equipotential surfaces are spherical shells.  V = kq/r where r = radius of the shell.
Equipotential surfaces are everywhere perpendicular to the lines of force (i.e. the electric field lines).
Computer drawings - EM Field program - 3D sources - electric potential, V     Fig. 17-6,   Fig. 17-7
For a charge q moving through a potential difference V, the change of potential energy is ΔPE = qV.
Definition:  1 electron volt = (electron charge) (1 volt),  That is,  1 eV = 1.60 x 10-19 C x 1V = 1.60 x 10-19 J.
Corona discharge - discharge of a conductor into the air producing a visible glow or spark.  Demo - high voltage source
Problems from Chapter 16.

13.

Friday, Dec. 18 - Q13
 

Capacitors - Any two conductors separated from one another by an insulator is a capacitor.
Definition:  capacitance = C = Q/V   where Q is the amount of charge on one of the conductors and V is the difference in potential between the conductors.   Units:  1 farad = 1 coulomb/volt,  1 F = 1 C/V
General equation for a parallel plate capacitor, C = K εoA /dK = dielectric constant (Table 17-3, p. 483),
     εo
 = permittivity of free space = 8.85 x 10-12 C2/N m2, A = area of one plate, d = plate separation.
Demo - large aluminum capacitor - measure C with a digital capacitor meter
More on corona discharge -- Video 27 - "Jacob's Ladder" (#8 - start at 3:40)
Inside a dielectric sandwiched between the plates of a capacitor, there is an induced polarization of the atoms.  This increases C, as shown in the demonstration.
Four kinds of capacitors:
   1.  cylindrical - low voltage - sheets of foil and paper wrapped up
   2.  nested parallel plate - high voltage - silicon oil for a dielectric
   3.  cylindrical - electrolytic - low voltage - high charge, high C, contains a liquid
   4.  variable - low C - air dielectric - interleaved metal plates - one set rotates
Video 28 - "Parallel Plate Capacitor"
Capacitors in parallel:  Cp = C1 + C2 + C3 + ...
Capacitors in series:  1/Cs = 1/C1 + 1/C2 + 1/C3 + ...
Energy storage in capacitors:  Demo - flash attachment, W  = 1/2 QV  = 1/2 CV2

14. Monday, Jan. 11
  Demo - high voltage (1000 V) applied to 5 capacitors in parallel (26 mF) - BOOM! - release of 13 J
Video 29 - "Energy Stored in a Capacitor"
Explanation of a cathode ray tube (CRT) - oscilloscope -  Fig. 17-20 on p. 486, TV - Fig. 17-21.
Chapter 18 - Electric Currents
Explanation of a zinc-carbon battery
Definition of emf (electromotive force) - a source of emf is any device that will transform nonelectrical energy into electrical energy.  e.g. battery, electric generator, solar cell
Video 30 - "Operation of a Battery"
Definition - electric current =
I = ΔQ / Δt , unit for current:  ampere (A).   1 A = 1 C/s
Analogy:  fluid flow - electric circuit
Definition - the direction of conventional current flow is opposite to the direction the electrons flow
Drift velocity - it is extremely slow - typically about 1 m per 5.5 hours!

15.

Wednesday, Jan. 13
 

(Georg) Ohm's Law - resistance = voltage / current
Demo - pass around a box of resistors, including one that has been cut open
Resistivity  ρ  of a wire of length L, cross-sectional area A and resistance RR = ρ L / A.    Table 18-1.
Variation of resistivity with temperature
Demo - heat a carbon resistor - R decreases slightly; cool it in liquid nitrogen - R increases
Video 31 - "Temperature and Resistance"
Color codes for resistors - page 499 - Fig. 18-12
Joule's Law for resistors:  power = P = I2R = VI = V2/R
Fuses and circuit breakers - page 505 - Fig. 18-19
Three-way switches, four-way switches

16.

Friday, Jan. 15 - Q16
  Demo - electrocuting a hot dog.  So what is in hot dogs to make them behave like semiconductors?
Superconductors - materials for which the resistivity  ρ  becomes zero as you lower the temperature through the phase transition temperature, Tc.   Graph of  R  vs. T.   Use a 4-point connection to avoid measuring contact resistance - demo
Superconductivity discoveries:
  1.  In 1911 in mercury by Kamerlingh-Onnes (Tc = 4.15 K)
  2.  In 1986 in La2CuO4 by Karl Muller and George Bednorz (who received the Nobel prize) (Tc = 35 K)
  3.  In 1987 in YBa2Cu3O7  (this is also called the "1-2-3 superconductor") by two groups (Tc = 92 K).
Demo - magnetic levitation with a 1-2-3 disk, a styrofoam boat, liquid nitrogen (T = 77 K) and a small magnet.
Video 32 - "Superconductivity:  Zero Resistance and the Meissner Effect"
Theory of superconductivity - Hyperphysics - Georgia State University - C. R. Nave
Superconductors Web site - includes the history
Superconductivity applications:
  1.  At Fermilab magnetic windings (wires) are cooled with liquid helium (4.2 K) so the wires are below Tc resulting in
      a tremendous savings in electricity (practically no "Joule heating").  The magnetic field of each 7-meter tubular
      magnet is 4.5 tesla.
  2.  "maglev" (magnetic leviation) trains in Japan, Germany and China (Shanghai).

  3.  Superconducting magnet in Science 114 - part of the 400-MHz NMR (nuclear magnetic resonance) equipment.  The
       outer part is cooled by liquid nitrogen (77 K).  The inner part is cooled by liquid helium (4.2 K).  The magnetic field is
       very strong (9.7 tesla) and is well regulated.  This field is created by means of a solenoid (coil of wire).  The wire
       consists of very fine strands of superconducting niobium-titanium clad in copper.  This is a Type II superconductor
       with a critical temperature Tc = 10 K.  NMR slides taken Jan. 20, 2004.  NMR cutaways - JEOL
Unassigned problem - 18-9 on page 516.

17.

Wednesday, Jan. 20
  Chapter 19.  DC Circuits
Kirchhoff's First (junction) Rule:  The algebraic sum of the currents at any junction in a circuit is zero.
Kirchhoff's Second (loop) Rule:  The algebraic sum of the changes in potential around any closed path in a circuit is zero.
Potential difference in a circuit - resistors, batteries
Demo:  6V battery, (variable) resistance box, two DMM's, wires  -  measure E and I, calculate R
Demo:  add a second resistance box.   Results:  spreadsheet with graph
Example of using Kirchhoff's rules - two batteries, 7 resistors
Internal battery resistance (ranges from 0.05 ohms for new batteries to 100 ohms for old ones)
Resistors in series:  Rs = R1 + R2 + R3
Resistors in parallel:  1/Rp = 1/R1 + 1/R2 + 1/R3
Demo:  three resistors (33 ohm, 56 ohm and 100 ohm) placed in series and then parallel  - measure R

18.

Friday, Jan. 22
  Video 33 - "Series and Parallel Circuits"
"Use of a Working Hypothesis" - series and parallel
Combining emfs in series and in parallel
Example of using Kirchhoff's rules - 3 equations in 3 unknowns
Program Kirch
! A True BASIC program that solves circuit problems using Kirchhoff's rules.
dim A(3,3), B(3,3),
I(3), V(3)
mat read A         ! read the coefficients
data 1,1,-1          !       
I1 +    I2       - I3  =    0
data -30,5,0        ! 
-30 I1   + 5 I2           =  -10
data 0,5,20         !             
5 I2 + 20 I3  =   10
mat read V          ! read the voltages
data 0,-10,10
mat B = inv (A)    ! find the inverse of matrix A
mat I = B*V         ! solution - calculate the currents
print "  The currents are:"
print "   
I1 = "; I(1)
print "   
I2 = "; I(2)
print "   
I3 = "; I(3)
end

When the program is RUN, the results are:

  The currents are:
   
I1 = 0.35294118
   
I2 = 0.11764706
   
I3 = 0.47058824

An Excel spreadsheet and a TI-83 method for solving this same problem.

RC circuits, time constant =  τ = RC
19. Monday, Jan. 25
  Chapter 20 - Magnetism
A magnetic field is caused by moving charges - Lorentz force equation - Fm = q v x B
Diagram showing magnetic field lines for several kinds of magnets - bar, neodynium, horseshoe
Demo - zinc coated iron fillings on overhead, magnetic field lines - applet
Video 34 - "Mapping Magnetic Field Lines"

(magnetic declination) = (direction of true north) - (direction of magnetic north)   |   map (Figure 3)
Dip needle -  here in the Quad Cities we are currently at about 55 degrees and the (magnetic declination) = 2oE.
Cross product of two vectors A and BC = A x B, three ways to find the direction of C ...
Magnitude of Fm = q v B sin θ
Video 35 - "Forces on an Electron Beam"

20.

Wednesday, Jan. 27
 

Demo:  Three glass tubes have a high voltage applied creating a plasma (bluish glow due to ionization of air molecules), deflect the beam with a magnetic field, round tube shows some fluorescence (green) when electrons hit the glass
Force on a current segment in a magnetic field, magnitude of the force = Fm = I L B sin θ
Magnetic field around a current carrying wire, B = μ0
I / 2 π r      μ0 = permeability of free space = 4π x 10-7 T-m/A
Two parallel current carrying wires
Video 36 - "Forces on a Current Carrying Wire"
Current balance apparatus used in lab - photo
Magnetic field at the center of a long solenoid, B = μ0 n
In = the no. of turns per unit length
Demo:  solenoid, DC power supply, digital Tesla meter, magna probe
Circular orbits of an electron in a uniform magnetic field, centripetal force = magnetic force

21.

Friday, Jan. 29
  Examples:  the Tevatron at Fermilab and the Large Hadron Collider at CERN
 v not parallel to B:  spiral path.  Occurs in nature around BEarth -  produces the aurora borealis
photos of Nov. 5, 2001  |  SpaceWeather.com  |  Aurorawebcam.com

Hall effect, Hall voltage = V = vd B l         Demo: digital Tesla meter, magnet...

Fractional quantum Hall effect
Nobel prize in physics in 1998
Dr. Daniel C. Tsui
Augustana graduate - 1961
Professor of Electrical Engineering at Princeton University
Book (in the Augustana library): "The Joy of the Search for Knowledge"
Scanning electron microscope lab (Science 115) named in his honor
Daniel and Linda Tsui Scholarship at Augustana College
Honorary degree from Augustana - May, 2004 - photos


Torque on a current loop (suspended vertically) in a magnetic field, 
τ = N I A B sin θ
How does a DC electric motor work?
Demo:  function generator - speaker - square wave - low frequency
How does a loudspeaker work?   Fig. 20-38
22. Monday, Feb. 1    Q22
 

Chapter 21.  Electromagnetic Induction and Faraday's Law - AC Circuits
Hans Christian Oersted (1819) - an electric current produces a magnetic field (Chapter 20)
Michael Faraday (1829) - a magnetic moving near a wire can produce an electric current
(Heinrich) Lenz's law:  An induced emf tends to set up a current whose action opposes the change that caused it.
Fig. 21-2.  Thrust a bar magnet into a coil connected to a galvanometer - illustration
Video 37 - "Induction of Current"

Definition:   magnetic flux  = 
Φ  =  B A cos θ,   unit for flux:  weber (Wb)
Faraday's law of induction:  Induced emf  =
ξ = - N ΔΦ / Δt  = - N Δ (BA cos θ) / Δt 
So changes of B, A, or θ
 will produce and induced emf.
The negative sign reflects Lenz's law: "An induced emf always produces a current whose magnetic field opposes the original change of flux."

Demo:
drop strong, small neodymium magnets into three tubes (PVC, aluminum, copper), time the fall, try two magnets.  Explanation...

23.

Wednesday, Feb. 3
  Motional emf, induced current in a circuit
Applications:  recording and playback heads in tape recorders, VCRs, floppy disks, hard disks
Electric generator (dynamo), motor - electrical to mechanical, generator - mechanical to electrical
Fig. 21-15 and Fig. 21-17.  An ac generator.
Generator theory: 
 ξ N B A ω sin (ω t),  ω =  the angular frequency (in rad/s),  ω = 2 π f, f = frequency in Hz.
Demo:  generator #1 - incandescent bulb (digital multimeter to measure ac volts), flicker bulb
Demo:
  generator #2 - (a) nothing - turns easily, (b) flashlight bulb, (c) a wire near a compass, (d) wrap the wire around the compass, what if there were several turns? (e) thermoelectric heat pump - Peltier (pelt-ee-yay) effect - turn crank one way (hot) and then the other (cold).  This is how the Coleman thermoelectric heat pump works.

Ring launcher - various rings - demo

24.

Friday, Feb. 5
  Solenoid doorbell (p. 567)   Fig. 20-27
Demo
: run a DC generator backwards - its a DC motor!
Alternator - demo - show an actual automobile alternator 

Transformers - Java applet - show examples - Fig. 21-25.
Video 38 - "Voltage Transformer"

Eddy currents are circular currents induced in the plane of a metal plate when passing through a changing magnetic field.
Demo:
  aluminum plate on a wooden pendulum swinging through a strong magnetic field
Video 39 - "Eddy Currents:  Force Acting on a Moving Conductor"

Inductance, L   Demo: various inductors (coils),
                       measure with a digital LRC meter
From experiment, induced emf =
ξ = - L ΔI / Δt
    Combine with Faraday's law to get  L = NBA /
I
    For a solenoid:  B =
μ0n I   so  L = μ0N2A / l
Energy (in joules) stored in a coil (inductor), i.e. in a magnetic field:  U = ½ L
I 2
LR circuit (battery, switch, inductor and resistor in series)
      Equation for
I ...,  time constant  = τ   = L / R
Chapter 18.  Section 7 - Alternating Current.
      AC voltage = V = V0  sin 2
πft
      AC current =
I = V / R = I0  sin 2πft        Fig. 21-35
      power delivered = P =
I 2R = I02 R sin 2πft
      
  Irms = 0.707 I0
         Vrms = 0.707 V0
         Ohm's law: Vrms =
Irms R

AC Instruments
An oscilloscope displays the instantaneous voltage V and the amplitude V0.
A digital multimeter connected across R and set on ac volts reads the rms voltage Vrms.
A digital multimeter connected in series with R and set on ac amps reads the rms current
Irms.
25. Monday, Feb. 8
  Demo - all in parallel:  function generator, resistor (100 Ω), speaker (8 Ω), DMM (ac volts), oscilloscope
        Results:  DMM (digital multimeter) reads Vrms = 0.707 volts
                     The oscilloscope displays the sine wave with amplitude = V0 = 1.00 volts
       (average power delivered) = Pave = Irms2 R = Vrms Irms

Chapter 21.
  Sections 12-14. 
       (inductive reactance) = XL = 2
π f L                  Fig. 21-36
       (capacitive reactance) = XC = 1/(2
π f C)           Fig. 21-37

R circuit
V and I are in phase:
φ = 0o

L circuit
V leads I :
φ = +90o

C circuit
V lags I :
φ = -90o

       RLC series circuit                  Fig. 21-39
          V = V0 cos (2
π f t +φ)
          impedance = Z = square root ( R2 + (XL - XC)2 )
         
φ = phase angle
          tan
φ = (XL - XC) / R
          phasor diagrams

Resonance in a series RLC circuit, equation for the resonant frequency... (when
φ = 0)
Demo - series RLC circuit - show input (across the function generator) and output (across R) on the oscilloscope
Computer simulation of an RLC circuit  - M1 - "Resonance", tuning a radio
Power in ac circuits, Pave =
Irms Vrms cos φ, φ = phase angle

26.

Wednesday, Feb. 10
 

Chapter 22.  Electromagnetic Waves

In 1865 James Clerk Maxwell published a set of four equations that basically unified electricity and magnetism.
Two results:  1. A changing magnetic field produces a changing electric field.
                    2. A changing electric field produces a changing magnetic field.
Electromagnetic waves are produced by accelerating charges.
Snapshot of an E-M wave, velocity c = f
λ,   Eo/Bo = c = 2.99792458 x 108 m/s (exact value - 1983)
Basic properties of electromagnetic waves...
Intensity of an E-M wave, energy density of E-M radiation
Fig. 22-8 (p. 620) - electromagnetic spectrum - sorted by wavelength (long to short):
   1. radio waves - AM/FM radio, TV
   2. microwaves - radar, cell phones, ovens
   3. infrared - remote controls, thermal radiation
   4. visible - human vision, solar energy - Roy G. BV (no I for indigo)
   5. ultraviolet - fluorescence of minerals, skin cancer
   6. x-rays - medical applications, reveal tooth decay, sample analysis (x-ray diffractometer - Room 114)
   7. gamma rays - tracers, cancer treatment

Video 40 - "Tesla - Master of Lightning" - watch the first part.  To be continued on Friday.

             There will be one or two questions on Test 3 about what you learn from this video.

Go to the Web page Tesla - Life and Legacy to read more about each section of the video.
  1.  Tesla's Early Years
  2.  Coming to America
  3.  War of the Currents
  4.  Harnessing Niagara
  5.  High Frequency
  6.  The Wireless?
  7.  Race of Robots - Cosmic Waves
  8.  Colorado Springs
  9.  Tower of Dreams
 10.  Poet and Visionary - Modern Prometheus
 11.  The Mad Scientist
 12.  A Weapon to End War
 13.  The Missing Papers
7:20
6:52
4:43
4:17
6:37
5:39
4:32
5:26
6:57
4:57
4:20
7:45
11:10
 
14:12
18:55
23:12
29:49
35:28
40:00
45:26
52:23
57:20
61:40
69:25
80:35


Nikola Tesla at age 29.

27.

Friday, Feb. 12
  Video: "Tesla - Master of Lightning" - watch the remainder.
Go to the Web page "Tesla - Inside the Lab" to obtain a description of Tesla's most important inventions:
    1. AC Motor
    2. Tesla Coil
    3. Radio
    4. Remote Control
    5. Improved Lighting
Explanation of the Tesla coil - demo
Tesla unit (1960)
Last update:  Feb. 9, 2010