physics 2b: lecture 1 secs. 11.1 - 11mulligangroup.ucr.edu/2bw2017lecture1.pdf · clicker questions...
TRANSCRIPT
Physics 2B: Lecture 1 Secs. 11.1 - 11.5
course organization
basic thermodynamics
course outline and organization
ALL THIS STUFF CAN BE FOUND ON THE ILEARN WEBSITE
course outline and organization
ALL THIS STUFF CAN BE FOUND ON THE ILEARN WEBSITE
course outline and organization
course outline and organization
Physics 2B: thermodynamics, fluids, and electricity and magnetism
8:10-9:00 AM MWF - Michael Mulligan
12:10-1:00 PM (full) and 3:10-4:00 PM (open) MWF - Stephen Wimpenny
office hours: Monday 9:30-11:30 AM
MS&E 342
textbook: University Physics for the Life Sciences by Knight, Jones, and Field
course outline and organization
Grading Policy:
discussion problems (once a week): 10%
midterm exam (February 6 from 8:10-9:00 AM): 20%
final exam (March 22 from 3:00-6:00 PM): 40%
homework (3 problem sets each week): 15%
in-class clicker problems (every class): 15%
course outline and organization
Grading Policy:
discussion problems (once a week): 10%
midterm exam (February 6 from 8:10-9:00 AM): 20%
final exam (March 22 from 3:00-6:00 PM): 40%
homework (3 problem sets each week): 15%
in-class clicker problems (every class): 15%
in previous years, about 85-90% of people passed with a grade of C- or better, 15-25% have gotten A- or better
approximate lower grade cutoffs (absolute grading scale): A-: 75%, B-: 60%, C-: 45%
clicker questions
CLICKER PROBLEMS BEGIN NEXT LECTURE (WEDNESDAY)
in-class clicker problems (every class): 15%
Grading scheme
correct answer: 3 points
incorrect answer: 1 points
no answer: 0 points
clicker questions
CLICKER PROBLEMS BEGIN NEXT LECTURE (WEDNESDAY)
in-class clicker problems (every class): 15%
Grading scheme
correct answer: 3 points
incorrect answer: 1 points
no answer: 0 points
clicker problems: based on the reading assignments for the current lecture — see Class Calendar tab in iLearn — or previous lecture
Clicker Test
Who is this?
A. Isaac Newton
B. Albert Einstein
C. Ludwig Boltzmann
D. Gandalf the Grey
Clicker Test
Who is this?
A. Isaac Newton
B. Albert Einstein
C. Ludwig Boltzmann
D. Gandalf the Grey
clickers
If you haven’t done so, please make sure you purchase and register a clicker by next class.
Note: Physics 2000 no longer supports IR clickers.
If you have one of these (yellow, orange, green stick-type clickers) you’ll need to replace it with the new grey model.
homework
homework (3 problem sets each week): 15%
accessible via Mastering Physics on iLearn
typical homework schedule:
Monday assignment is due Wednesday at 11:50PM
Wednesday assignment is due Friday at 11:50PM
Friday assignment is due the following Monday at 11:50PM
a guide to registering is in the Class Organization tab in iLearn
all assignments for a particular topic released on first lecture on that topic — 3 assignments released TODAY with the first due WEDNESDAY
homework
LATE HOMEWORK SUBMISSIONS WILL NOT BE ACCEPTED
if the graded homework assignments aren’t enough, we’re also providing additional problems that have some type of biological application for the concepts
these are NOT graded, even though, they have due dates
discussion sections
discussion problems (once a week): 10%
you should only attend the discussion section you’ve signed up for
discussion sections begin this Wednesday, January 11
these sessions will go over problem solving strategies while working problems and (hopefully) help you learn the material better
exams
Midterm: Monday, February 6 from 8:10 - 9:00 AM
Final: Wednesday, March 22 from 3:00 - 6:00 PM
midterm review session: Friday, February 3 sometime
final review session: Friday, March 17 sometime
exams
Midterm: Monday February 6 from 8:10 - 9:00 AM
Final: Wednesday March 22 from 3:00 - 6:00 PM
seating is un-assigned for the midterm and assigned for the final
things to know:
exams will begin on time and no additional time given if you arrive late
you need some type of picture ID for the exams
exams are closed book and notes; basic formulas and numerical constants will be provided
under normal circumstances: early or make-up exams will NOT be offered
Labs: Physics 2LB
the labs are run independently of Physics 2B
questions: please contact Prof. Hanson, who will be responsible for Physics 2LB this quarter
first lab sessions begin TODAY
course outline — see Course Calendar for details
thermodynamics: chapters 11 - 12 (2 weeks)
fluids: chapter 13 (1 week)
electricity and magnetism: chapters 20 - 25 (6 weeks)
we’ll go thru about one chapter each week
there are a lot of different concepts to learn and we’ll move fast
thermodynamics
goals/topics for this lecture
sections: 11.1-11.5
heat and the first law of thermodynamics
what’s thermodynamics?
what’s thermodynamics?
thermodynamics is the study of what can be said about a system without knowledge of its microscopic details
what’s thermodynamics?
thermodynamics is the study of what can be said about a system without knowledge of its microscopic details
in Physics 2A, you studied Newton’s law and its consequences
~F = m~a
what’s thermodynamics?
thermodynamics is the study of what can be said about a system without knowledge of its microscopic details
in Physics 2A, you studied Newton’s law and its consequences
~F = m~a
in the thermodynamics part of Physics 2B, we’ll study systems composed of “a lot” of particles in a box
our goal: to say what we can about the many-particle system
what’s thermodynamics?by “a lot,” I mean something like Avogodro’s number of particles 1023
in classical mechanics, to specify the “state” of the system, we’d need to specify the positions and velocities of each particle
keeping all of this information is rather challenging; furthermore, doing something with it is even harder
instead of keeping track of each particle individually, we think of them collectively in terms of macroscopic properties like
total mass of the system (kg)
pressure (Pa = N/m^2)
volume occupied (m^3)
number of particles
average kinetic energy (J)
what’s thermodynamics?
total mass of the system (kg)
pressure (Pa = N/m^2)
volume occupied (m^3)
number of particles
average kinetic energy (J)
these macroscopic properties describe the “state" the system
thermodynamics can sometimes be hard because not all of these macroscopic properties are independent (the minimal number of things you need to completely specific a system) or you can often say the same thing in many different ways
what this means is that you’ll have to familiarize yourself with this redundancy
macroscopic properties of a system
the average kinetic energy of a particle defines the system’s “temperature” T:
T / Kaverage
possible units for measuring temperature:
Kelvin (K)
Fahrenheit ( )�F
Celsius ( )�C
T (�C) =5
9
⇣T (�F )� 32�
⌘
T (K) = T (�C) + 273
temperature
T (K) � 0
temperature
the average kinetic energy of a particle defines the system’s “temperature” T:
T / Kaveragebecause we are thinking of temperature as the average kinetic energy — a non-negative quantity — we use Kelvin as our temperature unit
Lord Kelvin
temperature
T =2
3
Kaverage
kB
Natoms
= number of atoms
Ethermal
= Natoms
Kaverage
=3
2N
atoms
kBT
Boltzmann
0s constant = kB = 1.38⇥ 10
�23J/K
thermal energy
thermal energy is linearly proportional to temperature and number of particles
thermal energy
Ethermal
= Natoms
Kaverage
=3
2N
atoms
kBT
SI units for thermal energy: Joules (J)
another option: calories
1 calorie = 4.186 Joules
1 calorie is the energy needed to raise 1 gram of water 1 degree K
forms of energy (not entirely distinct)kinetic energy of motion: translations and rotations
potential energy: gravitational (later, we’ll study electromagnetic)
forms of energy (not entirely distinct)kinetic energy of motion: translations and rotations
potential energy: gravitational (later, we’ll study electromagnetic)
chemical energy: energy held in bonds between collections of atoms (again, we’ll study this more precisely later in the course)
forms of energy (not entirely distinct)kinetic energy of motion: translations and rotations
potential energy: gravitational (later, we’ll study electromagnetic)
chemical energy: energy held in bonds between collections of atoms (again, we’ll study this more precisely later in the course)
thermal energy: average kinetic energy
for the most part in the thermodynamics part of the course, we’ll only be interested in thermal energy and ignore these other forms
when there is friction, the plane and block heat up and gain thermal energy
thermal equilibriumtwo systems in thermal contact with one another are in thermal equilibrium if they have the same temperature: T1 = T2
suppose:T1 < T2
T1 < Teq < T2
then thermal energy will generally transfer between the two systems so that they equilibrate to the same temperature Teq
Teq Teq
T1 T2
thermal equilibriumtwo systems in thermal contact with one another are in thermal equilibrium if they have the same temperature: T1 = T2
suppose:T1 < T2
T1 < Teq < T2
then thermal energy will generally transfer between the two systems so that they equilibrate to the same temperature Teq
Teq Teq
T1 T2
Clicker Question (not for credit, only for fun)
In the previous example, where the two systems are each a collection of atoms in a box,
T1 < T2
T1 T2
are the (absolute) thermal energies of the two systems necessarily equal after they have equilibrated ?
A. YesB. No
T1 = T2
Clicker Question (not for credit, only for fun)
In the previous example, where the two systems are each a collection of atoms in a box,
T1 < T2
T1 T2
are the (absolute) thermal energies of the two systems necessarily equal after they have equilibrated ?
A. Yes
B. No
Why? soEthermal =3
2NkBT E1 6= E2 if N1 6= N2
T1 = T2
heat and the first law of thermodynamics
in this example, the change in the thermal energy of the two systems are of equal magnitude, but opposite sign
in this example, this change is called heat energy Q
Q1 = �Q2
T1 < T2
T1 T2
so �E1 = Q1 > 0
�E2 = Q2 < 0
Note: the change in energy of the total system composed of system 1 and system 2 does not change — energy conservation
heat and the first law of thermodynamics
T1 < T2
T1 T2
more precisely, we’ll typically consider two distinct ways that the thermal energy of a system can change:
1. transfer of heat to or from the system
2. performing work on or by the system
in this example, no work is done on system 1 (or system 2), only heat energy is transferred between the two systems
typically, if there is no work done on the system, but the thermal energy changes, there must have been some heat transfer
heat and the first law of thermodynamics
we’ll define work thru the typical example that we’ll consider
increase the pressure on a box of gas and don’t allow heat transfer
Ti 7! Tf
Ti < Tf
thermal energy change is equal to the work done if no heat is transferred
�E =3
2NkB(Tf � Ti) = W
heat and the first law of thermodynamics
we’ll define work thru the typical example that we’ll consider
increase the pressure on a box of gas and don’t allow heat transfer
Ti 7! Tf
Ti < Tf
thermal energy change is equal to the work done if no heat is transferred
�E =3
2NkB(Tf � Ti) = W
heat and the first law of thermodynamicsin general, the change of thermal energy of a system is due to heat loss or gained and work given or received
first law of thermodynamics
�E = Q+W
system environment
heat and the first law of thermodynamicsin general, the change of thermal energy of a system is due to heat loss or gained and work given or received
first law of thermodynamics
�E = Q+W
system environment
heat and the first law of thermodynamics�E = Q+W
Qs > 0 :system absorbs heat
Qs < 0 :system loses heat
Ws > 0 :work is done on the system
Ws < 0 :system does work
�Es > 0 : system gains thermal energy
�Es < 0 : system loses thermal energy
heat and the first law of thermodynamics�E = Q+W
Qs > 0 :system absorbs heat
Qs < 0 :system loses heat
Ws > 0 :work is done on the system
Ws < 0 :system does work
�Es > 0 : system gains thermal energy
�Es < 0 : system loses thermal energy
Clicker Question (not for credit, only for fun)
What is true about the heat ?
A.B.
Qs
C.
Suppose the environment does positive work on the system, but the temperature of the system does not change . Ti = Tf
0 < Ws = 35J
Qs = 35J
Qs = �35J
Qs = 0J
Clicker Question (not for credit, only for fun)
What is true about the heat ?
A.B.
Qs
C.0 =
3
2NkB(Tf � Ti) = Qs +Ws
Suppose the environment does positive work on the system, but the temperature of the system does not change . Ti = Tf
0 < Ws = 35J
Qs = 35J
Qs = �35J
Qs = 0J
summary
Ethermal =3
2NkBT
�Ethermal = Qs +Ws
next lecture
Secs. 11.5-11.7
heat engines and heat pumps