IB Physics
Energy, Power and Climate Change
Define the following terms:
thermodynamic engine
thermodynamic cycle
The second Law of Thermodynamics will be revisited in Topic 10. It is often stated in many ways.
“in a system, a process that occurs, will tend to increase the total entropy of the Universe”
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Visit the resource page link and write brief statements for the following variations on the 2 nd Law:
Clausius statement
Kelvin statement
The two features that are required in a thermodynamic engine are that
1. the engine must work in cycles
2. there must be at least two heat reservoirs
In the context of the two features listed above, and in conjunction to the 2 nd Law of Thermodynamics,
explain why no thermodynamic engine can operate at 100% efficiency (converting 100% of thermal
energy into mechanical work).
Define and explain the term degraded energy
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IB Physics
Energy, Power and Climate Change
As a result of energy degradation, the efficiency of a thermodynamic process (any energy conversion
process) can be determined by:
To describe energy transfer in a process, it is useful to draw a Sankey diagram that illustrates how
energy is transferred in proportion to the total energy input. For a typical power station, a simple
Sankey diagram looks like this:
In this example, the boiler is the hot reservoir. Thermal energy from fuel is transported as steam to be
converted into mechanical energy in the turbine. The rotating turbine turns the generator to make
electrical energy. The widths of the arrows drawn represent the amount of energy relative to the input
energy from the fuel.
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IB Physics
Energy, Power and Climate Change
Here is a Sankey diagram for an Ipod.
Determine the proportions of input energy that
are transferred to light, heat and sound.
Generation of Electricity
Summarize the basic steps on how commercial electricity is generated.
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Energy, Power and Climate Change
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Energy, Power and Climate Change
Complete the following table:
Energy Source
Renewable ?
CO2 Emission ?
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Other notes
IB Physics
Energy, Power and Climate Change
Distinguish between renewable and nonrenewable energy sources.
Define energy density of a fuel. Use values from the table below to discuss how the choice of fuel is
influenced by its energy density.
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IB Physics
Energy, Power and Climate Change
The great debate: List some advantages and disadvantages of the significant energy sources. Include
all principle energy sources and the common alternative energy proposals.
Read the information in the online text and answer the questions on the following page.
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Energy, Power and Climate Change
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Energy, Power and Climate Change
This sub-topic is by far the largest and the most time consuming. Much of it is just content but there is
some physics applied. I suggest you read the online text and answer the questions that follow. In
addition, I have selected some examples of where the physics often shows up on assessments. Work
through the section in the book and see how the physics is applied. This is the one part of Topic 8 that
we will spend a little time on in August so bring your questions.
Some hints and areas to work through (just do it!)
1. Know your units! Quite often, many problems can be worked correctly just by looking at how
the units cancel out (dimensional analysis). It is therefore critical that you understand the
units for all the quantities and variables in the equations in the Data Booklet. (for example, be
very clear what a watt (W) is!!!!)
2. Fuel consumption problems
 fuel consumption problems often include the following quantities: energy density,
efficiency, power output
 think of the problem in the context of the processes happening in real life for
example, in an oil fired electrical generating station:
i.
ii.
iii.
iv.
oil is burned at a certain rate (kg s-1)
each kg burned liberates a certain amount of thermal energy (energy density)
the conversion of the thermal energy to electrical energy is not 100% efficient
combining the above gives the rate that output energy is produced ie POWER
3. Solar power problems
 involve the conversion of solar energy into electrical energy in a photocell
 of the incoming solar radiation, only a portion reaches the Earth’s surface (about
45%).
 Intensity is a measure of power per unit area. This is important in terms of a solar
collector with area A and determining the rate of energy input from a light source of
a given intensity I.
4. Wave power problems
 always involve the use of “falling water” and its change in potential energy. These
problems can be complicated.
 As ΔPE = mgΔh, the mass of the “falling water” is required. This is determined
from the volume and the density. These calculations involve the following variables:
o the length of the wave front
o λ the wave length
o A the amplitude of the wave (wave height above flat water)
o  the density of water
o f the frequency of the wave (or tide)  needed to figure out the amount of
energy converted per unit time
5. Wind power problems
 similar to wave and water problems. IB study guide is great for this. I will post
images from the relevant pages.
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Energy, Power and Climate Change
A nice summary table:
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Energy, Power and Climate Change
Again this is a lot of reading with some interesting physics mixed in. The Stephan Boltzmann law will
be revisited when we study Astrophysics. Black body radiation is also covered in that topic as well as
being looked at as part of Nuclear Physics. Read through the chapter and answer the questions.
Determining the Surface Temperature of the Earth:
A modeling exercise using the Bristol ChemLabS Climate Model
Terms you need to understand before you begin.
Albedo
A is the albedo or reflectivity of the earth, it is a measure of the amount of cloud in the sky and ice on
the surface. If the Earth’s surface was all ice (Snowball Earth) then A would be 1.0.
τIR
τIR is the amount of infra red light from the earth that passes through the atmosphere and escapes to
space. If all the infra red light from the earth passes through the atmosphere without being absorbed
then τIR = 1.0, if all the infra red light from the earth is absorbed by the atmosphere then τIR = 0.0.
Greenhouse gases in the atmosphere are responsible for absorbing this infra red light, so as their levels
increase, τIR becomes smaller and more heat is trapped, warming the surface of the Earth.
τVIS
τVis is the amount of visible light from the sun that passes through the atmosphere and reaches the
surface. If all the light from the sun passes through the atmosphere without being absorbed then τVIS
= 1.0, if all the light from the sun is absorbed by the atmosphere then τVIS = 0.0.
Solar Constant %
The Solar Constant changes the suns energy that reaches the Earth. The standard value for this is
1370Wm-2
Instructions:
i.
Download the Java applet from the new IB Physics wiki.
ii.
Visit the Climate Change Modeling Exercise link on the wiki
a. The BIG IDEA is that the Earth’s surface temperature depends on the balance between
energy absorbed and energy emitted. If the temperature remains constant, these two
values are equal.
A simple model would represent this relationship as:
ksolar   RE2   4 RE2T 4
Make sure you understand what all the variables in this equation mean.
Plug values into this model to solve for T, the surface temperature on Earth
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IB Physics
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A more complicated model introduces albedo () and emissivity (). The
equation would look like this. Again, make sure you understand the terms.
2
2 4
solar
E
E
(1   )  k
  R   4 R T
b. Many of the variables in the above equation are relatively constant. List the constants
in the equation and their values (with units)
iii.
iv.
v.
It is clear that this model still only tells part of the story and the rest is much more complicated
and involves the atmosphere. Read through the Modeling Exercise and then play with applet
values. It will help to understand the diagram below first (feel free to add annotations as all
the symbols and notations get pretty intense)
Produce some plots to show how albedo, visible radiation and IR affect surface temperature.
Use the applet to generate values. Comment on how the IR absorption is related to surface
temperature and the greenhouse effect.
Define surface heat capacity and relate the Data Booklet equation for temperature change over
time to the model that you have been working with.
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The big idea in this sub-topic is to relate the greenhouse effect in the previous topic to changes in the
Earth’s systems that are collectively referred to as the issues of global warming.
Keep in mind the following as you do your reading:
1. Outline the major problems associated with global warming
2. Describe how the greenhouse effect is “enhanced” by human activities.
3. Describe how the global warming propagates itself. That is to say, some of the effects of global
warming produce subsequent effects that cause further warming.
4. What evidence supports the idea that global warming is happening and it is a serious problem.
5. Describe some methods of reducing the enhanced greenhouse effect.
If you get a chance watch Al Gore’s film “An Inconvenient Truth”
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