Swain Hall West- 1st Floor

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Web site: http://physics.indiana.edu/~courses/p340/S10/

Swain Hall West- 2nd Floor

AI office on third floor 340

LibraryPhysics Forum Lectures

CALM system

NOTE: To get full credit for the semester’s CALM portion of the course, you need to answer 75% of the semester’s CALM questions.

P340 Lecture 2-- CALM• Concisely describe the fundamental physical

significance/meaning of the absolute temperature of an object. (no response from 8 students; 5 others gave answers not covered by the following)• It is the tempurature from which the object is relative to

absolute 0. (concentrates on “absolute”, I was trying to emphasize “temperature”; about 3 responded like this).

• The significance is that absolute temperature measures the energy (heat) of an object. (8 responses like this).

• The absolute temperature of an object is the hotness measured on some definate scale (4 responses)

• The last of these is the best, (right from the book), but what is “Hotness”. Temperature is that quantity that tells us how heat flows when two objects are in thermal contact

P340 Lecture 2-- CALM

• THERMAL EQUILIBRIUM: • Two systems are said to be in thermal equilibrium if,

when they are brought into thermal contact, NO NET HEAT EXCHANGE takes place.

• Zeroth law of thermodynamics• If two systems (A and C) are both in thermal equilibrium with a third

system (B), then they are in thermal equilibrium with each other. (conventional statement)

• “There exist things called thermometers” (DVB’s statement; thermometers allow you to predict how and whether heat will flow when two objects are brought into thermal contact, but quantifying their “hotness”)

P340 Lecture 2• THERMOMETERS:

• Primary (PT): Some easily measureable physical quantity is a well-understood function of temperature

– Ideal gas (constant volume) thermometer: P =(N/V)kBT

– Black Body Radiation: (I(n) =(8ph/c3)(1/(exp(hn/kBT) -1))

– Paramagnetic Salt magnetization: (M = cH/(T –q))

– Johnson Noise of a resistor: (vrms = (4kBTR)1/2

• Secondary (ST): Some easily measureable physical quantity is a well-characterized function of temperature

– Thermal expansion (Hg, alcohol, bimetallic strips, etc.)

– Electrical resistance of Pt, Ge, carbon, Si diodes etc.

– Thermocouples

• The difference is the universality of the relationship between the measured quantity and the temperature. PT’s tend to be complicated to use, most often one uses calibrated ST’s.

One or at least few points needed for calibration;NIST worries about these

P340 Lecture 2“CMB fit to BB spectrum”

http://www.astro.ucla.edu/~wright/CMB.html

• The plot on the right shows data from the FIRAS instrument on the original COBE satellite experiment. The measurement of interest here was the set of residuals (i.e. the lower plot of the differences between the measured spectrum and that of a true black body)

• The curves correspond to various non-ideal BB spectra:• 100 ppm reflector (e)• Effect of hot electrons adding extra

60ppm of energy just about 1000 yrs after the big bang (m just before 1000 yrs, y just after)

P340 Lecture 2“Practical Thermometry”

• International Temperature Scale (ITS-90)

• This is the accepted standard against which secondary thermometers are typically calibrated (it deviates from absolute temperature in certain regions by several mK).• 0.65-5K (3He or 4He equil. vapor pressure over liquid)

• 3.0 to 24.5561 K (He gas thermometer calibrated at defined fixed points)

• 13.8033 to 1234.93 K (Pt resistance thermometer calibrated at defined fixed points with set interpolation scheme).

• Above 1234.93 K: Planck radiation law.

P340 Lecture 3(Example: Adiabatic compression)

P340 Lecture 3(CALM)

Recalling your knowledge of quantum systems from P301, concisely describe how the micro states available to a system may be influenced by the system’s macrostate (e.g. its volume, energy etc.).• The macro-state of a system determines the micro-states that are available to

the system by, for example:• Defining the quantum states available to the “individual” particles (e.g.

linear dimensions, magnetic field strength and orientation, etc.)• Defining the number of such microstates.• Putting limits on which of those ‘defined’ states can actually be occupied.

(e.g. if the energy of the whole system is E, you can’t put more than that much energy into any one particle!)

• Important point: the microstate of the whole system is what we are concerned with (complete set of quantum numbers of ALL particles, not just the state of a single particle; or classically, specifying the momentum and position of each particle in the system).

P340 Lecture 3“Probability and Statistics”

• Bernoulli Trials• REPEATED, IDENTICAL, INDEPENDENT, RANDOM

trials for which there are two outcomes (“success” prob.=p; “failure” prob=q) – EXAMPLES: Coin tosses, queuing problems, radioactive

decay, scattering experiments, 1-D random walk,…

• A question of fundamental importance in these problems is: Suppose I have N such trials, what is the probability that I have “n” successes? The answer is:

P(n) = N!/[n!(N-n)!] pn(1-p)N-n

We will spend a bit of time looking at this distribution.