Inquiry: Solar cooker
Name: ……………………………..
Teacher:…………………….
Date Set:………………….
Subject:
11 Physics
Progress Check:……………….
Due Date: …………………
Conditions of assessment:
 Write your name and date on the paper
 You must adhere to the school assessment policy
 This cover sheet must be attached to your assignment
This sample courtesy of Darrin Timms
Focus Areas: KCU, IP, & EC
Task Type: ERT
Context: Today SOLAR ENERGY supplies just 1.5 GW - less than one per cent of the worlds energy needs. Estimates of
how big solar energy will become vary from 5 per cent to 50 per cent of the worlds energy needs by 2050. One
thing is clear, the use of clean energy will dramatically increase, driven by the issues of global warming, and
depletion of reserves of fossil fuels. Several technologies need to be examined when discussing solutions to the
worlds energy needs. One of these is solar thermal power. Solar thermal power plants or Concentrating Solar
Power Plants, produce electricity in much the same way as a coal fired power station. The only difference is that
the steam is produced by sunlight rather than burning coal.
Task: Your task is to answer the following question: “Can a recycled Austar dish be a viable alternative energy source for
the average home user?” You will make a statement in answer to the research question that says either “A
recycled Austar dish can be a viable alternative energy source for the average home user? or that it cannot be. You
will need to support your argument with results obtained in class. Your article should include the following:

Introduction: (600 words)
o Discuss the growing threat of global warming and the exhaustion of fossil fuels as a way of contextualising
the need for renewable energy sources such as solar energy. You should make it clear how this impacts on
you.
o Research the E.M. spectrum, energy, optics, specific heat, wavelength and frequency as necessary and link
these concepts to task question. If they do not directly relate to the question then they are not relevant. This
will provide the concepts and terms to be used later.
o Research the topic Solar Thermal Energy and how it could be part of the mix of renewable energy solutions.
o State examples of where Thermal Solar Plants are currently in use and relevant facts about their energy
output.
o State the advantages of this technology, and the projected growth of this technology.
o Create a variables grid that shows the factors that impact on this technology.

Results: from class experiment using an Austar dish. Must be in tabular form. Graphs must be labelled and
included here. Consider graphing different variables against each other to identify patterns, trends and
interrelationships (many of the results will be analysed as a class and collated together as secondary data).

Discussion (500-600 words):
o
Analyse your tabulated and graphical results in a meaningful manner that will allow you to draw a conclusion
later. Include % error calculations.
o
Justify your conclusions with the following: you need to explore the scenarios you have tested and
researched to decide if a recycled Austar dish can be a viable alternative energy for the average home user?
Your argument should have about three major points in support of your opening statement (your thesis). In
your arguments you should explain the results in terms of the following concepts and interrelationships:
refraction, reflection, focal point, focal length, centre of curvature, specific heat capacity, thermal conduction,
absorption, emission, radiation, wavefronts. You must cite data to support your explanations.
o
Calculate and compare the amount of useable solar energy obtained from the Austar dish to the average
amount of raw solar energy hitting the earth. Then compare this value to the average house hold.
o
Compare the efficiency of the Austar dish to photovoltaic cells
o
Construct and use the variables grid to identify possible sources of error which may have affected the energy
efficiency compared to the photovoltaic cell and the raw energy of the sun.
o
Discuss (and justify) possible modifications and refinements you could make to the design to improve the
energy efficiency of the Austar dish.
Conclusion
Bibliography


Knowledge and
Conceptual Understanding
EXIT STANDARDS

 Linking and application of algorithms, concepts,
principles, theories and schema to find solutions in
complex and challenging situations.

Systematic analysis of primary or secondary data
to identify relationships between patterns, trends,
errors and anomalies
 Students compares and explains the
complex concepts and interrelationships
between light, energy and optics
D
B
 Students compares and explains the
concepts of light, energy, optics

Student explains the concepts of
light, energy, optics

Student describes light, energy and
optics


Student has linked and applied
algorithms, concepts, principles, theories
and schema to find a solution to finding
alternative viable energy sources in the
home in complex or challenging
situations.

Student has applied algorithms,
principles, theories and schema to find a
simple solution for viable alternative
energy sources

Student has applied algorithms,
principles, theories an schema relating
to light, energy, and optics


Student analyses the primary and
secondary data to identify patterns and
trends, errors and anomalies between
energy, optics, light and specific heat

Student analyses the primary and
secondary data to identify obvious
patterns and trends, errors and
anomalies between energy, optics, light
and specific heat

Identification of obvious patterns and
errors
 Student collects data

Student has linked and applied
algorithms, concepts, principles, theories
and schema to find a solution to finding
alternative viable energy sources in the
home in complex and challenging
situations.
 Student systematically analyses the
primary and secondary data, trends and
patterns, errors and anomalies in this
data to identify the relationships
between energy, optics, light, specific
heat
C
B
 Has identified, and justified any possible
outliers and has made links between these
effects on the energy efficiency
 Uses % error calculations to support
argument regarding the use of recycled
Austar dishes in the home.
 Has identified possible outliers and has
described their affects on the calculated
results
 Has performed % error calculations
 Has identified possible outliers in
experiment
 Has qualitatively identified errors in
experiment


 exploration of scenarios and possible outcomes with
justification of conclusions/ recommendations
 Explains and explores the average home
energy consumption and makes links
with argument regarding the use of
recycled Austar dishes in the home
 Explores possible ways of converting
solar thermal energy obtained from
Austar dish into useable energy in the
home
 Explores possible modifications and
refinements to improve % efficiency of
Austar dish and makes links to different
variables and experimental errors.
 Has described the average home energy
consumption and has made links with the
argument regarding the use of recycled
Austar dishes in the home
 Has described some methods of
converting light energy to useful energy
 Has described modifications to Austar
dish design to improve its efficiency.
 Has described the average home energy
consumption.
 Has described some methods od
converting light energy to useful energy
 Has described modifications to design of
the Austar dish








 analysis and evaluation of complex scientific
interrelationships
Evaluating & concluding
Investigative processes
comparison and explanation of complex concepts,
processes and phenomena relating to Solar
Thermal Energy
A
Student recognizes simple isolated
phenomena
Recording of data
Teacher notes
Equipment:
 Austar mirror dish and stand
 100mL beaker
 Data logger and thermometer probe/gun
 Ruler
 String
 Tape measure
 Light intensity probe
 Cardboard
 Red light intensity probe
Procedure:
Create a variables grid
1.
Using the photovoltaic cell, measure and calculate the energy/m2
2
Measure the light intensity emitted from the sun and convert to watts/m2
1 lux = 1.464x10-7 watts/cm2
3.
Use cardboard to qualitatively determine the position of the focal length of the dish
4.
Suspend the beaker at the focal length and calculate the temperature change of the beaker and calculate the
energy emitted
5.
Move the beaker at different intervals slightly above and below the “focal point”  repeat to gather average
results
6.
Use the data from 4. To graph and determine the focal point of the dish. Calculate the energy at this point
7.
Calculate this energy per m2 by measuring the diameter of the austar dish and calculating its area. Energy/ m2
8.
Using mathematical manipulation skills, determine the theoretical value of the focus point (mirror/lens formula)
9.
Get the students to compare these values and explain why they might not match
10.
Get the students to design a new dish that will minimize spherical aberration (changing to parabolic curve rather
than spherical using auto cad etc)
11.
Get students to create a variables grid of all of the possible errors and explain how those errors will affect their
results
12
Statistically analyse results
13
Calculate the carnots engine formula to measure efficiency
14
Calculate the angle of deviation- reflective error due to the refraction through the mirror
15
Discuss heat transferrance and discuss the movement of the sun and how the focal point does not change when
the sun moves
16.
Possible extensions:
- Change the colour of the beaker to absorb as much heat as possible ie. Black vs white vs
transparent vs blue etc
-
Calculating specific heat and Latent Heat:
1. Heat the water in a beaker using the data logger to obtain the following graph:
temperature
Time
time = rate / temperature
Rate of Heating :
(units = oC /min)
Q/min = SPH x Mass x Temperature/min
(units = Joules/min)
2. Then if you calculate the weight of mass lost over a specific time period (e.g. 10 mins). But the beaker must be boiling
first.
i.e. initial mass (@100oC)= 200g; and final mass (10 mins later after continuous boiling) = 175g
Thereforem = 25g
(massfinal –massinitial)
Qto boil = Q/min x time
Eg. Lets say that Q= 2516 and the time that we boiled was for 10mins, therefore:
= 2516 x10
= 25160 Joules of energy in 10 mins
Latent heat = Qused / mass = J/g
Calculating the focus point of a Austar dish
There are 5 ways to find the focus point of an austar dish:
1.
2.
3.
4.
5.
Measure
CAD
Graphmatica
Spherical model
Parabolic model
1. Measure:
Using Austar dish and a piece of cardboard, adjust the cardboard to find the most concentrated light and measure
how far this is from P (along the principal axis) errors include: parallax error, finding the prinicipal axis, movement of
cardboard while measuring, measurement units. Repeat this experiment several times to get an average
2. CAD
3. Graphmatica
4. Spherical model
Assuming that the dish is spherical:
Lets say that the chord is 1000mm and depth is 200mm
200mm
1000mm
Therefore the model on the graph would look like:
200
500
r
r- 200
r
Using pythagoras’s theorem:
C2 = A2 +b2
Where c= radius of circle (r)
A= 500
B = r-200
Therefore:
R2= y2 + x2
= 5002 + (r-200)2
= 250 000 + (r-200)(r-200)
= 250 000 + r2 – 200r -200r + 40 000
= 290 000 + r2 -400r
2
2
R -r = 290 000 -400r
0 = 290 000 – 400r
-290 000 = -400r
-290 000/-400 = r
725 = r
Therefore the focus point = ½ r
= 725/2
= 360cm
5. Parabolic model
500
(x,y)
(500, r-200)
(o,f)
F-y
P(x,y)
200
Y+d
500
Dimetrix
Y = -d
Q
Y = ax2
@ (500,200)dimt.
200 = a 5002
A = 200 /5002
= 8 x 10-4
Therefore, y = 8x10-4x20
Now: fp = pQ
( x o ) 2  ( f  y ) 2  y  d
x 2 ( f  y )2  y d
@(1000, 800)
10002  ( f 800) 2 800 d
@( 200, 3200)
20002  ( f 3200) 2 3200 d
20002  ( f 3200) 2 3200
2400
2400 
20002  ( f 3200) 2 
10002  ( f 800) 2 800
10002  ( f 800) 2
x 2 1600x 164
2400 2  x 2  160 x  164
0  x 2  160 x  5.76  106