More on Black Bodies

What we strictly have to cover in the Syllabus

8.5.3.2.1  That is focus area 5 column 2 point 1

define the relationship between the 
temperature of a body and the
dominant wavelength of the radiation
emitted from that body 

On the most basic level a body is an object of more than a few hundred atoms, and the hotter it is the more blue it is.

Blackbodies are a class of bodies that were theoretically discussed in 1860 by a scientist call Kirchoff,
Simply put anylight falling on them get absorbed so that any light coming from them has been generated by the body. Now for the next 40 years scientist fooled around making blackbody radiators, then taking spectra. Finally they got black body spectra and Planck modeled it and this lead to Modern Physics, but that is another story

 1900 was close enough to make do calculations. 2009 we are getting close but we are still not there, light goes in and never comes out, only the heat light comming from the body.  So far "blackbody" only really turns up next year in the HSC Astrophysics Option.

So the modern defintion of a Blackbody radiator is

A blackbody allows all incident radiation to pass into it (no reflected energy) and internally absorbs all the incident radiation (no energy transmitted through the body). This is true of radiation for all wavelengths and for all angles of incidence. Hence the blackbody is a perfect absorber for all incident radiation

Siegel, Robert; Howell, John R. (2002). Thermal Radiation Heat Transfer; Volume 1 (4th ed.). Taylor & Francis. p. 7. ISBN 1-56032-839-8. http://books.google.com/books?id=O389yQ0-fecC&pg=PA7.

So here is my summary from the point of view of a spectroscophist, baring in mind

Most things coffee cups and stars, are good black body radiators in the visible, perfect in the infrared, and to varying degrees poor in the UV. So if you use the black body Weins law that looks at the peak wavelength, you get a good temperature, if you use an infrared bolometer that looks at the curve in the IR you get a great reading, and UV you get a more or less view of the structure of what you are looking at.  That is how different it is from a little Pt box with carbon nano tubes in it.

This is a plot of how badly stars deviate from the BBR curve (black) in the UV which people dont use to determine temperature, because the curve is not valid there.  Basically the is not a fix surface for a surface temperture.  Stars get hotter in the inside, and so there is no defined temperature.  Supergiants have colder outer layers to the UV escape surface is higher. The curves above  represent UV deficit

More in depth is given in this web text http://cseligman.com/text/sun/blackbody.htm

This is from, http://homepages.wmich.edu/~korista/sun-images/solar_specbb.jpg  as you can see

1. IR good
2. Peak fair
3. UV lousy

I would interpret this as the UV light powering, more visible light from the sun but this is an observation not a published piece of science.

Planck's Vision

How to understand Electrons

1. Metals are regular 3D array of positive nuclei (example Mg++ nuclei)
2. Electrons(example e- and e- from the Mg++) swim around the nuclei

2.1 Here is a realistic picture of electrons swimming around a metal, They are not "classical electrons" but actually give bulk to the metal (dont worry until you do Quantum Mechanics at UNI)

3. Electrons are like trout in a tank, the walls are like the WORK FUNCTION

4. There are three ways to get electrons out of a metal

4.1 Fire an ion from a low pressure gas (throw a rock in the trout pond and trout will jump out)

4.2 Heat up the metal called THERMIONIC EMISSION (Heat it up Elmo?)

4.3 Hit out the electrons with UV light PHOTOELECTRIC effect (Laser)





Is there a relationship between metal lattice distances and resistivity?

What a great site Web Elements is !
The red ones are the d block standard metals.
Copper, silver gold are in a line copper silver gold
Iron is dark grey, mercury light grey.
The last period is has many null values

What do you think? Does a large r (top) lead to low resistivity (bottom)?  

Do magnetic field lines exert a pressure?

There is a model of magnetic field taught in New South Wales schools that predicts how two magnets or a magnet and wire will behave:

Step 1: For two devices draw independent field.

Step 2: Draw the resultant fields.

Step 3: The resultant diagram has area of high and low field density, the field lines are given the properties of gas molecules that exert some sort of packing pressure against items in the diagram.

So in the above diagram there are

(A) 6 lines outside 4 lines inside ....outside wins the wires attract.

(B) 6 lines outside 12 inside  ..... to crowded inside repel.

Here is for a motor from Electrical Science Fundamentals Handbook

This is a neat visualization guide,  if the lines where springs they would push the conductor.

Comment 1: The maths F = BilSin(theta) considers the field only at the conductor.
Comment 2: The fields do not interact, but sum.
Comment 3: Faraday was completely non mathematical, and offered "lines of force" as a non scientific guide.  Maxwell tried to develop this into "tubes of force" to attempt a mathematical explanation. This was abandoned some 150 years ago.
Comment 4: The discovery of the electron and special relativity means magnetic fields from currents are understood as an extension of electrostatics.  Magnetic fields from permanent magnets are explained by Quantum Mechanics and special relativity. This presents a problem to a high school teacher as this is outside the breadth of school physics.
Comment 5: This path back to electrostatics still does not clear away for deep understanding.  Force at a distance can be managed by the construct of fields, which is a mathematical device that overlays an answer field.  The exchange of virtual particles radiating over distance is used by Quantum Field Theory and Feymann
diagrams.  The curvature of space, created by mass or charge, then telling the other particle how to move has been developed by Einstein's General Relativity. The most up to date theory is 'bane' theory, string theory or M theory.


This a to look at

How to Study Lectures

Space Physics Brain Teasers

Can you figure out the Rocket Science Equation that goes with this picture?

..... or this one ?

... or this one ?

Chemicals on the web - Cubane.

Computer simulated molecules are a great way to learn Chemistry.  When I found out about Cubane C8H8 I thought it was time to review how to "Surf" the web and see new molecules.


There are a number of great web rendering of  molecules: 

1. JMOL  
How?  Search your molecule on Google + "JMOL"
Good things - any browser, any molecule
Bad - can bend bonds


2. CHIME
How? 1. Download Chime plugin,  send in info to publisher
then search Chime + Molecule.
Good things: Can "Scupt" molecules and get a real feel for them
Bad things: you can only show your class on your data projector/ IWB

3. CanvasMOL
How? Just follow this link
Good things: Fast and molcule focused.

Cubane!

Gravity acts through out an object in free fall !

Penrith High reaches + 9 g force in Lab.

Actually it was just swirling a marble in a mop bucket.

The bucket wall was 84 degrees. g x 1/cos(84) = 9.5 g.

Students were asked to calculate the mass required to cause this acceleration at 15 cm in the center of the bucket.

The difference between the bucket and gravitation is that the bucket applies a force at the point of contact of the marble and force pushes and stress through out the marble, where as a gravitational field would tug uniformly throughout the marble. Gravitation gently accelerates the whole marble.

If you were in the marble, in the bucket you would be crushed to death, were as in the gravitational field as the force is spread evenly through out your body you would feel "Weightless". This is also why comets are not crushed as they swing near the Sun.

I am always looking for this explanation in Textbook, as without it it is most confusing.