Course Webpage: http://panda.unm.edu/Courses/Thomas/Phys161fa10/P161Syllabus.htm

Course Grading Policy

You will want to get Mastering Physics and an iClickerRegistration info on the webpage

Key Points:

Seven Midterms (Drop lowest score)No makeup examsScantron but NOT multiple choiceModel Exams Posted at least 2 weeks before midterm0.1% of missed exam points for each problem done/ clicker quiz

(up to a maximum of 50%)

Chapter 17 Young&FreedmanSome things are hot, some things are cold.

Heating (usually) causes expansion.

In thermal contact, two objects (eventually) reach the same temperature.

Daniel Gabriel Fahrenheit (1686–1736)Fahrenheit temperature:

The zero point was determined by placing the thermometer in brine: a mixture of ice, water, and ammonium chloride, a salt. This is a frigorific mixture.

96 degrees, was the level of the liquid in the thermometer when held in the mouth or under the armpit of his wife.

Celsius used ice/water and water/steam for 0 and 100.

Gases also expand on heating.

Demo

Kelvin temperature

€

TF =9

5TC + 32°

TK = TC + 273.15 Units: K

The ‘size’ of 1K = 1°C

What is the approximate boiling temperature of water, in K?

A] 100 K

B] 212 K

C] 273 K

D] 373 K

E] 485 K

Solids also (usually) expand on heating.

If I heat this metal annulus,The hole will:

A] get smaller

B] get bigger

C] stay the same size

Last time: Heat = Energy (that is transferred because of a difference in temperature).[The temperature difference may be VERY small!]

“Specific Heat”, c, is the amount of heat needed to raise the temperature of a mass of material a degree (or a Kelvin)

Q=mc

“Latent heat” (of vaporization, or of fusion) is heat per mass of material needed to boil (vaporize) or freeze (fuse).

Today: equilibration of water & icemechanisms of heat transfer

Mixing Ice & Water

Mechanisms of heat transfer

1. Conduction 2. Convection (flow of fluid, like air)3. Radiation

Two square (in cross-section) glass rods connect very large copper blocks held at

different temperatures.

Which rod conducts heat faster?

A] Rod A

B] Rod B

C] They conduct heat at the same rate

Radiation.

Hot objects emit light (glowing red hot, white hot, light bulb filaments, etc.)

€

dQ

dt= AeσT 4 e = emissivity, e=1 is a ‘BLACK BODY’

Room temp: infrared emission Very hot: white emission VV hot: blue

We can measure (approximately) the temperature of an object by looking at

its black body spectrum. (This assumes that emissivity is

independent of wavelength, which is often nearly true.)

If an object can emit EM radiation (light, or infrared or UV etc.),then it must also absorb EM radiation.

Consider an object in a vacuum box with perfectly reflective walls at temperature T. In thermal equilibrium, the object is emitting

radiation:

Since it does not change temperature, it must absorb the same amount of radiation.

So e= emissivity = absorptivity!Black objects heat up faster in the sun, but cool off faster at night! €

dQ

dt= AeσT 4

The ideal gas law:

A] Works with T (temp) in celsius or Kelvin, but you need to use a different R for each.

B] Works with T in °C, °F, or K, but you need to use a different R for each.

C] Works with T in °C or K, but if you use °C you need to use the “gauge pressure”, not absolute pressure

D] Works only and exclusively with T in Kelvin.

An ideal gas at 200 K occupies 2 liters at a pressure of 1 atm.

If the gas is compressed to 1 liter of volume, what will be its temperature?

A] 200 K

B] 400 K

C] 800 K

D] There is not enough information to determine this!

An ideal gas at 200 K occupies 2 liters at a pressure of 1 atm.

If the gas is compressed to 1 liter of volume, and the pressure is 2 atm, what will be its temperature?

A] 200 K

B] 400 K

C] 800 K

D] There is not enough information to determine this!

20 liters of Argon are in thermal equilibrium with 20 liters of Helium. (These are monatomic gases, Mar=40, Mhe=4.)

Which molecules have more kinetic energy, on average?

A] Argon

B] Helium

C] Both have the same

Which molecules are moving faster, on average? HELIUM

MON Aug 30

W= Work Done BY a Gas =

€

pdVV1

V2

∫Memorize!

When gas does work, it loses internal energy

(unless energy is added, via heat.)

When it does negative work, it gains internal energy

A gas in a piston is taken from state 1 to state 2. The outside pressure is higher than the pressure in the cylinder.

For which path does the gas do the largest positive work? A

For which path does the gas do the most negative work?(I.e. for which path is the most work done ON the gas)

Or chooseE] no path does work of this sign

In the isobaric process shown, W is: +

A] +

B] -

C] 0

D] cannot determine

In the isobaric process shown, U is: +

In the isobaric process shown, Q is: +

In the isochoric process shown, W is: 0

A] +

B] -

C] 0

D] cannot determine

In the isochoric process shown, U is: -

In the isochoric process shown, Q is: -

In the isothermal process shown, W is: +

A] +

B] -

C] 0

D] cannot determine

In the isothermal process shown, U is: 0

In the isothermal process shown, Q is: +

Let’s do this quantitatively.

Wed Sept 1

On expanding isothermally from 2L to 4L, an ideal gas does 6J of work, as the pressure drops from 2 atm to 1 atm.

By how much must it expand to do an additional 6J of work?

A] It must expand an additional 2L, to reach 6L

B] It must double again, to 8L

C] It must increase four-fold, to 16L

D] It can do no more work, as it has reached 1 atm.

E] Cannot determine without knowing T

In the mystery path process shown, W is: D

A] larger than for an isothermal process from A->B

B] smaller than for an isothermal process from A->B

C] 0

D] cannot determine

In the mystery path process shown, U is: 0

In the mystery path process shown, Q is: D

How much work is done when an ideal gas is expandedfrom V1 to V2 at constant pressure?

A] 0

B] nRT2

C] nRT1

D] nR(T2-T1)

E] it depends on whether is it monatomic or diatomic.

What is the difference in internal energy of the gas at points 1’ and 2 ? A

For the cyclic process shown, W is: D

A] 0, because it’s a loop

B] p0V0

C] - p0V0

D] 2 p0V0

E] 6 p0V0

For the cyclic process shown, U is: A

For the cyclic process shown, Q is: DFor ONE cycle:

Fri sept 3

For the constant pressure ideal gas process shown, The change in internal energy U of the gas is

A] nCv

B] nCp

C] 0

D] cannot determine

If the gas is monatomic and ideal, for the constant pressure process shown, the change in internal energy can also be expressed as:

A] pV

B]

C]

D] €

12 pΔV

€

32 pΔV

€

52 pΔV

(use a paper & pencil)

A non-ideal gas is taken from A to B. The gas does 3 J of work; 6 J of heat is added to the gas.What is the internal energy of the gas at B?

A] 3 J

B] 9 J

C] 10 J

D] cannot determine, since gas is non-ideal

E] the numbers given are not physically possible

A non-monatomic ideal gas is taken from A to B. The gas does 3 J of work; 6 J of heat is added to the gas.What is the internal energy of the gas at B?

A] 3 J

B] 9 J

C] 10 J

D] cannot determine, since gas is non-monatomic

E] the numbers given are not physically possible