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Review for Test 3
Introduction Section 0 Lecture 1 Slide 1
Lecture 27 Slide 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Review for Test 3
Introduction Section 0 Lecture 1 Slide 2
Lecture 27 Slide 2
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet
*Homework Handout
PHYSICS OF TECHNOLOGY - PHYS 1800 ASSIGNMENT SHEET
Spring 2009 Date Day Lecture Chapter Homework Due Feb 16 17 18 19 20
M Tu W H F*
Presidents Day Angular Momentum (Virtual Monday) Review Test 2 Static Fluids, Pressure
No Class 8 5-8 5-8 9
-
Feb 23 25 27
M W F*
Flotation Fluids in Motion Temperature and Heat
9 9 10
6
Mar 2 4 6
M W F*
First Law of Thermodynamics Heat flow and Greenhouse Effect Climate Change
10 10 -
7
Mar 9-13 M-F Spring Break No Classes Mar 16 18 20
M W F*
Heat Engines Power and Refrigeration Electric Charge
11 11 12
8
Mar 23 25 26 27
M W H F*
Electric Fields and Electric Potential Review Test 3 Electric Circuits
12 13 9-12 13
-
Mar 30 Apr 1 3
M W F
Magnetic Force Review Electromagnets Motors and Generators
14 9-12 14
9
Apr 6 8 10
M W F*
Making Waves Sound Waves E-M Waves, Light and Color
15 15 16
10
Apr 13 15 17
M W F*
Mirrors and Reflections Refraction and Lenses Telescopes and Microscopes
17 17 17
11
Apr 20 22 24
M W F
Review Seeing Atoms The really BIG & the really small
1-17 18 (not on test) 21 (not on test)
No test week 12
May 1 F Final Exam: 09:30-11:20am * = Homework Handout
Review for Test 3
Introduction Section 0 Lecture 1 Slide 3
Lecture 27 Slide 3
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Notes on Test
1. Covers Chapters 9-11
2. ~8 short answer problems or questions (5 point each)
3. 3 Numerical problems based heavily on the material from the homework and Lab/Demo sessions (20 points each). One problem each from Chapters 9, 10 and 11.
4. You will have a formula sheet just like the one in the handout.
5. Test is Thursday March 26 1:30-2:45 in ESLC 46.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 4
Lecture 27 Slide 4
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Introduction and Review
Review for Test 3
Introduction Section 0 Lecture 1 Slide 5
Lecture 27 Slide 5
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
What Do We Need To Measure?
• What is the minimum about things we need to know?
• Where things are—a length, L• When things are there—a time, t
• How thing interact with gravity—a mass, M• How things interact with E&M—a charge, Q
• How thing inter act with weak nuclear force• How things interact with strong nuclear force
• Random collections of objects—a temperature, T
Review for Test 3
Introduction Section 0 Lecture 1 Slide 6
Lecture 27 Slide 6
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Describing Motion and InteractionsPosition—where you are in space (L or meter)
Velocity—how fast position is changing with time (LT-1 or m/s)
Acceleration—how fast velocity is changing with time (LT-2 or m/s2)
Force— what is required to change to motion of a body (MLT-2 or kg-m/s2 or N)
Inertia (mass)— a measure of the force needed to change the motion of a body (M)
Energy—the potential for an object to do work. (ML2T-2 or kg m2/s2 or N-m or J)
Work is equal to the force applied times the distance moved. W = F dKinetic Energy is the energy associated with an object’s motion. KE=½ mv2
Potential Energy is the energy associated with an objects position.Gravitational potential energy PEgravity=mghSpring potential energy PEapring= -kx
Momentum— the potential of an object to induce motion in another object (MLT -1 or kg-m/s)
Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT-1 or kg/s) and (MLT-2 or kg m/s2 or N)
Review for Test 3
Introduction Section 0 Lecture 1 Slide 7
Lecture 27 Slide 7
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Newton’s Laws in Review
• 1st Law —a special case of the 2nd Law for statics, with a=0 or Fnet=0 • An objects velocity remains unchanged, unless
a force acts on the object.
• 2nd Law (and 1st Law)—How motion of a object is effected by a force.– The acceleration of an object is directly
proportional to the magnitude of the imposed force and inversely proportional to the mass of the object. The acceleration is the same direction as that of the imposed force.
• 3rd Law —Forces come from interactions with other objects.• For every action (force), there is an equal but
opposite reaction (force).
F ma
units : 1 newton = 1 N = 1 kgm s2
Review for Test 3
Introduction Section 0 Lecture 1 Slide 8
Lecture 27 Slide 8
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Energy: The potential to do work.Conservation of Energy: The total
energy of a closed system remains constant.
– Energy can be converted from one form to another.
– Not all forms of energy can be fully recovered.
Conservation of Energy
Time
Ene
rgy
Review for Test 3
Introduction Section 0 Lecture 1 Slide 9
Lecture 27 Slide 9
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Momentum and Impulse• Multiply both sides of Newton’s second law by the time interval over which the force acts:
• The left side of the equation is impulse, the (average) force acting on an object multiplied by the time interval over which the force acts.
• How a force changes the motion of an object depends on both the size of the force and how long the force acts.
• The right side of the equation is the change in the momentum of the object.
• The momentum of the object is the mass of the object times its velocity.
vF
vaF
mt
tmm
net
net
p mv
Review for Test 3
Introduction Section 0 Lecture 1 Slide 10
Lecture 27 Slide 10
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Impulse-Momentum Principle
The impulse acting on an object produces a change in momentum of the object that is equal in both
magnitude and direction to the impulse.
impulse = change in momentum
= p
In analogy,
work = change in energy= ΔE
Review for Test 3
Introduction Section 0 Lecture 1 Slide 11
Lecture 27 Slide 11
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Formulas We Know and Love
Formulas as They Will Appear on the Test Sheet
221 tatvd o 2
21 tto
r
vac
2
t
ddv of
t
of
2r
mmGF ba
gravity
t
vva of
tof
22
3
2
3
4a
b
b
a
a Gm
T
R
T
R
amF Inet G=6.67·10-11 N-m2/kg2
dFW lF g=9.8 m/s2 2
21 mvKEtrans 2
21 IKErot mghPEgravity
tFp tL
mvp IL xkFelastic
t
WPower
2mrI 2
21 xkPEelastic
Review for Test 3
Introduction Section 0 Lecture 1 Slide 12
Lecture 27 Slide 12
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Review for Test 3
Introduction Section 0 Lecture 1 Slide 13
Lecture 27 Slide 13
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Test 3 Review ConceptsConcepts and Terms to Be Familiar With
Know what pressure and density are and how this relates to fluids.Know Pascal’s Principle and how to apply it to hydraulics problems.Know how buoyant force is related to pressure and Archimedes’ Principle.Know what an ideal gas is and what the ideal gas law says about pressure volume and temperature of an ideal gas.
Understand how conservation of mass is related to flow rate.Understand the difference between laminar and turbulent flow.Understand Bernoulli’s Principle as a fluid form of the conservation of energy.
Be able to state the four laws of thermodynamics.Be able to define heat and temperature and explain how they are different.Understand heat capacity, heat of fusion (melting), and heat of vaporization (boiling).Be able to do simple calorimitry problems.Be able to qualitatively explain the difference between the three forms of heat transfer: conduction, convection and radiation.
Be able to explain what a heat engine is and what the components of work, high temperature reservoir and low temperature reservoir.What is efficiency of a heat engine? Of a Carnot engine?
Review for Test 3
Introduction Section 0 Lecture 1 Slide 14
Lecture 27 Slide 14
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Formulas We Know and Love
New Formulas as They Will Appear on the Test Sheet
AFP / Vm / TNkPV B kB=1.38 10-23 J/K
Avrateflow constant221 hgvP VPW
TcmQ H
CHH Q
QQQWe
/
H
CHCarnot T
TTe
Review for Test 3
Introduction Section 0 Lecture 1 Slide 15
Lecture 27 Slide 15
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Fluids and Pressure
Review for Test 3
Introduction Section 0 Lecture 1 Slide 16
Lecture 27 Slide 16
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Test 3 Review Concepts
Concepts and Terms to Be Familiar With
Know what pressure and density are and how this relates to fluids.
Know Pascal’s Principle and how to apply it to hydraulics problems.
Know how buoyant force is related to pressure and Archimedes’ Principle.
Know what an ideal gas is and what the ideal gas law says about pressure volume and temperature of an ideal gas.
Understand how conservation of mass is related to flow rate.
Understand the difference between laminar and turbulent flow.
Understand Bernoulli’s Principle as a fluid form of the conservation of energy.
Fluids and Pressure
Review for Test 3
Introduction Section 0 Lecture 1 Slide 17
Lecture 27 Slide 17
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
States of Matter
Review for Test 3
Introduction Section 0 Lecture 1 Slide 18
Lecture 27 Slide 18
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Pressure
• The man weighs more, so he exerts a larger force on the ground.
• The woman weighs less, but the force she exerts on the ground is spread over a much smaller area.
• Pressure takes into account both force and the area over which the force is applied.– Pressure is the ratio of the force to
the area over which it is applied:
– Units: 1 N/m2 = 1 Pa (pascal)– Pressure is the quantity that
determines whether the soil will yield.
P F
A
Review for Test 3
Introduction Section 0 Lecture 1 Slide 19
Lecture 27 Slide 19
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Dennison’s Laws of Fluids
• When push comes to shove, fluids are just like other stuff.
• Pascal’s Principle: Pressure extends uniformly in all directions in a fluid.
• Boyle’s Law: Work on a fluid equals PΔV
• Bernoulli’s Principle: Conservation of energy for fluids
Review for Test 3
Introduction Section 0 Lecture 1 Slide 20
Lecture 27 Slide 20
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Pascal’s Principle
• Fluid pushes outward uniformly in all directions when compressed.
• Any increase in pressure is transmitted uniformly throughout the fluid.
• Pressure exerted on a piston extends uniformly throughout the fluid, causing it to push outward with equal force per unit area on the walls and the bottom of the cylinder.
• This is the basis of Pascal’s Principle:– Any change in the pressure of a
fluid is transmitted uniformly in all directions throughout the fluid.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 21
Lecture 27 Slide 21
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Pascal’s Principle for Gases
• Gas molecules lack strong interactions.• Pressure is understood as resulting from
momentum transfer to the container walls through unbalanced collisions
• Pressing on one surface adds force and hence imparts impulse to the gas
• That impulse is taken up as added collisons (pressure) on other surfaces
• The random nature of the motion of gas particles assures that the force is distributed evenly to all surfaces
• For fixed walls, a decrease in V results in an increase in P
• For expandable walls (like a balloon) the volume “appears elsewhere to make up for the lost volume
Review for Test 3
Introduction Section 0 Lecture 1 Slide 22
Lecture 27 Slide 22
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Pascal’s Principle for Liquids
• Liquid molecules have strong interactions.• Liquids do not compress much• Pressure is understood as resulting from
momentum transfer to the container walls through unbalanced spring forces
• Pressing on one surface adds force that is transferred to other springs
• The network nature of the forces on the particles assures that the force is distributed evenly to all surfaces
• For expandable walls (like a balloon) the volume “appears elsewhere to make up for the lost volume
• For fixed walls, a small decrease in V (a compression) results in a large increase in P
• For solids, you can think of the strong forces holding the atoms in there equilibrium positions, equivalent to fixed walls
+
+ ++
+ ++
+ + +
+ +
+
+ +
+
+ ++
+ ++
+ +
+
+ + +
+ +
++ +
+
+ +
Review for Test 3
Introduction Section 0 Lecture 1 Slide 23
Lecture 27 Slide 23
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Archimedes’ Principle• The average density of an object compared to a fluid determines
whether the object will sink or float in that liquid.• The upward force that pushes objects back toward the surface in
liquids is called the buoyant force.• Archimedes’ Principle: The buoyant force acting on an object
fully or partially submerged in a fluid is equal to the weight of the fluid displaced by the object.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 24
Lecture 27 Slide 24
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Archimedes’ Principle
• For example, consider a block submerged in water, suspended from a string.– The pressure of the water pushes on the block from all sides.– Because the pressure increases with depth, the pressure at the bottom of the block
is greater than at the top.– There is a larger force (F = PA) pushing up at the bottom than there is pushing
down at the top.– The difference between these two forces is the buoyant force.
The buoyant force is proportional to both the height and the cross-sectional area of the block, and thus to its volume.
The volume of the fluid displaced is directly related to the weight of the fluid displaced.
Weight mg VdgVolume Ah
Excess Pressure P W
A
dgAh
adgh
Review for Test 3
Introduction Section 0 Lecture 1 Slide 25
Lecture 27 Slide 25
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Flow Rate
• The volume of a portion of water of length L flowing past some point in a pipe is the product of the length times the cross-sectional area A, or LA.
• The rate at which water moves through the pipe is this volume divided by time: LA / t.
• Since L / t = v, the rate of flow = vA.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 26
Lecture 27 Slide 26
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• Laminar flow is smooth flow, with no eddies or other disturbances.– The streamlines are roughly parallel.
– The speeds of different layers may vary, but one layer moves smoothly past another.
• Turbulent flow does have eddies and whorls; the streamlines are no longer parallel.
Laminar vs Turbulent Flow
Review for Test 3
Introduction Section 0 Lecture 1 Slide 27
Lecture 27 Slide 27
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Bernoulli’s Principle
• How does a large passenger jet manage to get off the ground?
• What forces keep it in the air?• How is a ball suspended in mid-air by
a leaf blower?• What happens if we do work on a
fluid?• Bernoulli’s principle applies
conservation of energy to the flow of fluids:
• The sum of the pressure plus the
• kinetic energy per unit volume of
• a flowing fluid must remain constant.
constantE/V 2
1 2 ghvP
constantE 2
1
constant
2
mghmvPV
EPEKEWork Total
Review for Test 3
Introduction Section 0 Lecture 1 Slide 28
Lecture 27 Slide 28
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
How does pressure vary in pipes and
hoses?
• Will the pressure be greatest in the narrow section or the wide section?
• The speed will be greater in the narrow section.• To keep the sum P + 1/2 dv2 constant, the pressure must be
larger where the fluid speed is smaller (h is fixed).• If the speed increases, the pressure decreases. (This goes
against our intuition.)• This can be shown using vertical open pipes as pressure
gauges.• The height of the column of water is proportional to the
pressure.
Pressure Changes with Area
Review for Test 3
Introduction Section 0 Lecture 1 Slide 29
Lecture 27 Slide 29
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Review for Test 3
Introduction Section 0 Lecture 1 Slide 30
Lecture 27 Slide 30
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Temperature and Heat
Review for Test 3
Introduction Section 0 Lecture 1 Slide 31
Lecture 27 Slide 31
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Test 3 Review Concepts
Concepts and Terms to Be Familiar With
Be able to state the four laws of thermodynamics.
Be able to define heat and temperature and explain how they are different.
Understand heat capacity, heat of fusion (melting), and heat of vaporization (boiling).
Be able to do simple calorimitry problems.
Be able to qualitatively explain the difference between the three forms of heat transfer: conduction, convection and radiation.
Temperature and Heat
Review for Test 3
Introduction Section 0 Lecture 1 Slide 32
Lecture 27 Slide 32
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Dennison’s Laws Thermal Poker(or How to Get a Hot Hand in Physics)
• 0th Law: Full House beats Two Pairs
• 1st Law: We’re playing the same game (but with a wild card)
• 2nd Law: You can’t win in Vegas.
• 3rd Law: In fact, you always loose.
• 0th Law: Defines Temperature
• 1st Law: Conservation of Energy (with heat)
• 2nd Law: You can’t recover all heat losses (or defining entropy)
• 3rd Law: You can never get to absolute 0.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 33
Lecture 27 Slide 33
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• What is heat?• What is the relationship between quantity of heat
and temperature?• What happens to a body (solid, liquid, gas) when
thermal energy is added or removed?
Thermal Energy
Heat
Solid: Atoms vibrating in all directions about their fixed equilibrium (lattice) positions. Atoms constantly colliding with each other.
Liquid: Atoms still oscillating and colliding with each other but they are free to move so that the long range order (shape) of body is lost.
Gas: No equilibrium position, no oscillations, atoms are free and move in perpetual high-speed “zig-zag” dance punctuated by collisions.
gas
liquid
solid
Review for Test 3
Introduction Section 0 Lecture 1 Slide 34
Lecture 27 Slide 34
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• When two objects at different temperatures are placed in contact, heat will flow from the object with the higher temperature to the object with the lower temperature.
• Heat added increases temperature, and heat removed decreases temperature.
• Heat and temperature are not the same.
• Temperature is a quantity that tells us which direction the heat will flow.
Heat is a form of energy.(Here comes conservation of energy!!!)
Temperature and Heat
Review for Test 3
Introduction Section 0 Lecture 1 Slide 35
Lecture 27 Slide 35
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Gas Behavior and The First Law
Consider a gas in a cylinder with a movable piston. If the piston is pushed inward by an external force, work is done on
the gas, adding energy to the system.
• The force exerted on the piston by the gas equals the pressure of the gas times the area of the piston: F = PA
• The work done equals the force exerted by the piston times the distance the piston moves:
W = Fd = (PA)d = PV
Review for Test 3
Introduction Section 0 Lecture 1 Slide 36
Lecture 27 Slide 36
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• In an isothermal process, the temperature does not change.– The internal energy must be constant.– The change in internal energy, U, is zero.– If an amount of heat Q is added to the gas, an equal amount of work
W will be done by the gas on its surroundings, from U = Q - W.
• In an isobaric process, the pressure of the gas remains constant.– The internal energy increases as the gas is heated, and so does the
temperature.– The gas also expands, removing some of the internal energy.– Experiments determined that the pressure, volume, and absolute
temperature of an ideal gas are related by the equation of state:
PV = NkT where N is the number of molecules
and k is Boltzmann’s constant.
Ideal Gas Behavior
Review for Test 3
Introduction Section 0 Lecture 1 Slide 37
Lecture 27 Slide 37
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• The specific heat capacity of a material is the quantity of heat needed to change a unit mass of the material by a unit amount in temperature.– For example, to change 1 gram by 1 Celsius degree.– It is a property of the material, determined by experiment.– The specific heat capacity of water is 1 cal/gC: it takes 1
calorie of heat to raise the temperature of 1 gram of water by 1C.
• We can then calculate how much heat must be absorbed by a material to change its temperature by a given amount:
Q = mcT where Q = quantity of heatm = massc = specific heat capacityT = change in temperature
Heat and Specific Heat Capacity
Review for Test 3
Introduction Section 0 Lecture 1 Slide 38
Lecture 27 Slide 38
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
If the specific heat capacity of ice is 0.5 cal/gC°, how much heat would have to be added to 200 g of ice, initially at a temperature of -10°C, to raise the ice to the melting
point?
a) 1,000 calb) 2,000 calc) 4,000 cald) 0 cal
m = 200 gc = 0.5 cal/gC° T = -10°C
Q = mcT = (200 g)(0.5 cal/gC°)(10°C) = 1,000 cal
(heat required to raise the temperature)
Review for Test 3
Introduction Section 0 Lecture 1 Slide 39
Lecture 27 Slide 39
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• When an object goes through a change of phase or state, heat is added or removed without changing the temperature. Instead, the state of matter changes: solid to liquid, for example.
• The amount of heat needed per unit mass to produce a phase change is called the latent heat.– The latent heat of fusion of water corresponds to the amount of heat
needed to melt one gram of ice.– The latent heat of vaporization of water corresponds to the amount of
heat needed to turn one gram of water into steam.
Phase Changes and Latent Heat
+
+ +
+
+ +
++ +
Solid
Review for Test 3
Introduction Section 0 Lecture 1 Slide 40
Lecture 27 Slide 40
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
If the specific heat capacity of ice is 0.5 cal/gC°, how much heat would have to be added to 200 g of ice, initially
at a temperature of -10°C, to completely melt the ice?
a) 1,000 calb) 14,000 calc) 16,000 cald) 17,000 cal
Lf = 80 cal/g Q = mLf = (200 g)(80 cal/g) = 16,000 cal
(heat required to melt the ice)
Total heat required to raise the ice to 0 °C and then to melt the ice is: 1,000 cal + 16,000 cal = 17,000 cal = 17 kcal
Review for Test 3
Introduction Section 0 Lecture 1 Slide 41
Lecture 27 Slide 41
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
A hot plate is used to transfer 400 cal of heat to a beaker containing ice and water; 500 J of work are also done on the contents of the beaker by stirring. What is the increase in internal energy of the ice-water mixture?
a) 900 Jb) 1180 Jc) 1680 Jd) 2180 J
W = -500 JQ = 400 cal
= (400 cal)(4.19 J/cal) = 1680 J
U = Q - W = 1680 J - (-500 J)= 2180 J
Review for Test 3
Introduction Section 0 Lecture 1 Slide 42
Lecture 27 Slide 42
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
A hot plate is used to transfer 400 cal of heat to a beaker containing ice and water; 500 J of work are also done on the contents of the beaker by stirring. How much ice melts in this process?
a) 0.037 gb) 0.154 gc) 6.5 gd) 27.25 g
Lf = 80 cal/g = (80 cal/g)(4.19 J/cal) = 335 J/g
U = mLf
m = U / Lf = (2180 J) / (335 J/g) = 6.5 g
Review for Test 3
Introduction Section 0 Lecture 1 Slide 43
Lecture 27 Slide 43
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
The Flow of Heat
• There are three basic processes for heat flow:
– Conduction
– Convection
– Radiation
Review for Test 3
Introduction Section 0 Lecture 1 Slide 44
Lecture 27 Slide 44
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
The Flow of Heat
– In conduction, heat flows through a material when objects at different temperatures are placed in contact with one another. L
TAk
t
Q
Review for Test 3
Introduction Section 0 Lecture 1 Slide 45
Lecture 27 Slide 45
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
– In convection, heat is transferred by the motion of a fluid containing thermal energy.
• Convection is the main method of heating a house.• It is also the main method heat is lost from buildings.
The Flow of Heat
Review for Test 3
Introduction Section 0 Lecture 1 Slide 46
Lecture 27 Slide 46
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
The Flow of Heat
– In radiation, heat energy is transferred by electromagnetic waves.
• The electromagnetic waves involved in the transfer of heat lie primarily in the infrared portion of the spectrum.
• Unlike conduction and convection, which both require a medium to travel through, radiation can take place across a vacuum.
• For example, the evacuated space in a thermos bottle.
• The radiation is reduced to a minimum by silvering the facing walls of the evacuated space.
428
4
/107.5 KmW
TA
B
BtQ
Review for Test 3
Introduction Section 0 Lecture 1 Slide 47
Lecture 27 Slide 47
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 27
Review for Test 3
Heat Engines and the Second Law
Review for Test 3
Introduction Section 0 Lecture 1 Slide 48
Lecture 27 Slide 48
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Test 3 Review Concepts
Concepts and Terms to Be Familiar With
Be able to explain what a heat engine is and what the components of work, high temperature reservoir and low temperature reservoir.
What is efficiency of a heat engine? Of a Carnot engine?
Heat Engines and the Second Law
Review for Test 3
Introduction Section 0 Lecture 1 Slide 49
Lecture 27 Slide 49
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Heat Engines
It is a device that uses input heat to generate useful work.
From the 1st Law (Conservation of Energy)
In cyclic engines we return to the original state every cycle so
What is a heat engine?
Review for Test 3
Introduction Section 0 Lecture 1 Slide 50
Lecture 27 Slide 50
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Heat Engines
All heat engines share these main features of operation:– Thermal energy (heat) is
introduced into the engine.– Some of this energy is
converted to mechanical work.
– Some heat (waste heat) is released into the environment at a temperature lower than the input temperature.
What is a heat engine?
Review for Test 3
Introduction Section 0 Lecture 1 Slide 51
Lecture 27 Slide 51
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Efficiency
Efficiency is the ratio of the net work done by the engine to the amount of heat that must be supplied to accomplish this work.
Or from the 1st Law
Review for Test 3
Introduction Section 0 Lecture 1 Slide 52
Lecture 27 Slide 52
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
A heat engine takes in 1200 J of heat from the high-temperature heat source in each cycle, and does 400 J of work in each cycle. What is the efficiency of this engine?
a) 33%b) 40%c) 66%
QH = 1200 JW = 400 Je = W / QH
= (400 J) / (1200 J)= 1/3 = 0.33= 33%
Review for Test 3
Introduction Section 0 Lecture 1 Slide 53
Lecture 27 Slide 53
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Carnot Efficiency
• The efficiency of Carnot’s ideal engine (one using an ideal gas with PV=NkBT) is called the Carnot efficiency and is given by:
• This is the maximum efficiency possible for any engine taking in heat from a reservoir at absolute temperature TH and releasing heat to a reservoir at temperature TC.
• This provides a useful limiting case.• Even Carnot’s ideal engine is less than 100% efficient.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 54
Lecture 27 Slide 54
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Second Law of Thermodynamics
• You can’t recover all heat losses .
• You can’t win in Vegas.
• No engine, working in a continuous cycle, can take heat from a reservoir at a single temperature and convert that heat completely to work.
• Therefore, no engine can have a greater efficiency than a Carnot engine operating between the same two temperatures.
• Define entropy (something that measures randomness or disorder in an object) to take account of this.
Heat (random motion) is a special form of energy that cannot be fully (with complete efficiency) transformed to other forms of energy.
This leads to various forms of the Second Law of Thermodynamics.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 55
Lecture 27 Slide 55
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
A Third Statement of The Second Law of Thermodynamics
• Entropy remains constant in reversible processes but increases in irreversible processes.
• The entropy of a system decreases only if it interacts with some other system whose entropy is increased in the process.
– This happens, for example, in the growth and development of biological organisms.
• The entropy of the universe or of an isolated system can only increase or remain constant. Its entropy can never decrease.
Review for Test 3
Introduction Section 0 Lecture 1 Slide 56
Lecture 27 Slide 56
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
A heat pump uses 200 J of work to remove 300 J of heat from the lower-temperature reservoir. How
much heat would be delivered to the higher-temperature reservoir?
a) 100 Jb) 200 Jc) 300 Jd) 500 J
W = 200 JQC = 300 JQH = W + QC
= 200 J + 300 J= 500 J
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