Solar Energy Experiment: Light Transferred to Heat

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Objective

SWBAT collect evidence through experimentation that light energy from the sun can be transferred to thermal energy (heat).

Big Idea

Students conduct an experiment testing how various colors absorb different amounts of light by measuring the amount of heat energy created.

Rationale and Preparation

The Why Behind Teaching This: 

Unit 3 addresses standards related to the transfer of energy and matter between organisms in an ecosystem.  The unit begins with identifying what solar energy is and what two forms of energy solar energy provides to life on Earth.  This is an important foundation for understanding standard 5-PS3-1: Use models to describe that energy in animals' food (used for body repair, growth, motion, and to maintain body warmth) was once energy from the sun.  We build on this knowledge throughout the unit in other lessons related to photosynthesis and how animals use the energy they get from food.  In this unit students will also be conducting experiments to gather evidence to support their belief that plants get the materials they need for growth from either water, air, or the soil.  This is covered in standard 5-LS1-1: Support an argument that plants fet the materials they need for growth chiefly from air and water. Students will be creating food chains and food webs to describe the movement of matter among organisms in an ecosystem.  This is covered in standard 5-LS2-1: Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment.

I combined these three standards all into unit 3 because teaching them together allows students to see how they are all connected.  The energy that plants get from the sun is stored in their parts until animals consume them.  Plants cannot absorb this energy and reproduce without other materials from the environment such as carbon dioxide from the air, and water and nutrients from the soil.  The animals that consume the plants use part of the energy for growth, reproduction, etc. but they also store some of the energy.  That energy is then passed on to other  animals  once eathen.  All of the energy that is available in an ecosystem can ultimately be traced back to the sun.  Teaching all of these standards together, instead of in isolation of each other, makes that connection easier to see.    

This specific lesson is linked to standard 5-PS3-1 because it builds the foundation that energy from the sun can be absorbed and transferred to other forms of energy.  This will lead into plants absorbing and storing energy that is later used by animals.  The first two lessons of this unit demonstrate how light energy from the sun is converted to other forms of energy that can be seen or measured.  It is easier for students to understand something that they cannot see or measure, such as photosynthesis, after doing these early lessons.  This lesson also covers Standard 3-5-ETS1-3: Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. Students will be controlling variables to test which color absorbs the most light from the sun.  

Lesson Goal: 

The goal of this lesson is for students to demonstrate an understanding that light energy from the sun can be absorbed and converted to heat energy.   

Success Criteria:

They will demonstrate an understanding of this by collecting accurate data, in the form of the temperature change, of various colored envelopes to determine which absorbed the most hear, thus heating up the fastest.   

Preparing for Lesson:

Warm Up:

Have a piece of black paper and a piece of white paper ready to show the class for s'mores activity.   

Guided Practice: 

Explore: 

  • Graham cracker for each student 
  • Individually wrapped mini Hersheys bar for each student 
  • One large marshmallow for each student 
  • One envelope, per group, made of construction paper in each of the following colors: red, yellow, blue, green, orange, black, and white.  Watch the Video on how to make colored envelopes for step by step directions on how to make the envelopes. 
  • 7 thermometers per group 

Wrap Up: 

None 

Warm Up

10 minutes

Building Excitement Through A Treat: 

I begin today's lesson by writing the words SOLAR ENERGY on the white board.  I ask students to tell me what they know about this term.  They tell me that it is energy from the sun and then struggle to tell me anything else.  I push for more information by asking what forms of energy we get from the sun, and they tell me light and heat.  

I explain that we will be using solar energy to complete two activities today.  One thing we will be using solar energy for is to make solar powered s'mores.  The students immediately get excited.  I begin a conversation that will get them thinking about our other activity before I even tell them what the activity is.  

I hold up two pieces of paper, one black and one white.  I ask students which piece of paper would be better to make our s'mores on.  Students tell me the black because black heats up faster.  I ask them if anyone has any evidence or proof that this is true.  One student tells me that she went outside one time wearing all black and she was really hot.  I ask her if she also went outside on the same day and time wearing all white.  She said no.  I explained that she doesn't have anything to compare the black to, so her evidence doesn't prove that black gets hotter than white.  Another student said that he wore a black shirt one day and his friend wore white.  When they were outside playing at recess he got really hot and his friend did not.  I asked the class to consider what variables have changed in this example.   Students tell me that the color of shirt changed, the person in the shirt is different, the activities that they may have done at recess might be different, and that the boy in the white may have spent more time in shady areas then the boy in the black shirt.  I explain that there are too many variables that could have affected the temperature so that evidence is not valid to support the idea that black heat up faster than white.  

After this conversation, I introduce the second activity we will be using solar energy to complete.  I explain that we will be conducting an experiment to test if black really does heat up faster then white.  I tell students that we won't just be testing black and white, but we will also be testing yellow, red, blue, green, and orange. 

The Purpose In Having This Conversation: 

Spending the first ten minutes of the lesson consumed with the conversation above is important for several reasons.  It gets students thinking about science and practicing science terminology.  It also helps students see how the science they are learning about in class relates to things they experience in the real world.  By leading students into the discussion of proving their ideas to be true, it allows me to review concepts previously taught, such as variables, as well as make connections between various areas of science (all areas of science can be connected).  

Guided Practice

15 minutes

Setting up the Foldable for the Experiment: 

I provide each student with a trifold foldable that will be used for planning out the experiment.  I prefold these for the students to save time.  I place one on the overhead so that I can model completion for struggling students.  Having a visual for the ESE and ELL students, as well as those who struggle with writing and spelling, helps them complete the steps along with everyone else and not fall behind.  

I write the question in the inside, upper left hand flap, of the foldable.  The question we are answering through this experiment is Do different colors absorb different amounts of light? I use this time to discuss what is actually happening in this experiment.  I ask students how we are measuring the amount of light that is absorbed and they tell me which color heats up the most.  They are able to make this connection because of the conversation we had leading into this activity.  I explain that when light is absorbed, that energy can be transformed into other forms of energy, in this case thermal energy (heat).  I ask students to think about this related to a car, something they experience quite often.  When you go outside on a hot day, is it colder inside the car or hotter?  Students tell me hotter.  I explain that the light from the sun enters the car through the windows and gets trapped which heats up the car.  I ask them to think of some ways that people stop the light from entering, thus keeping their car cooler.  They tell me they park in garages, they use window covers, and that they tint their windows.  

Next, I provide my ESE and ELL students with the Solar Energy Envelope Experiment Steps that I have precut and put into ziplock bags for them.  I ask them to find the hypothesis square.  I begin the hypothesis on my foldable for the other students to copy down.  We always write our hypothesis as an if/then statement to show cause and effect relationship.  I write If I place a thermometer inside various colored envelopes (red, white, yellow, orange, green, blue, and black), then I predict _____________________.  I remind students they need to fill in the blank with what they believe will happen.  I leave the blank in my example because I do not want to write my hypothesis and influence what they may write.  I want them to think about the outcome on their own, and come up with their own ideas.  

Next, we list out the materials we will need.  While students copy down the list I write in the example on the overhead, I pass out the Solar Energy Envelope Experiment Procedure to all of the students who did not get all of the steps typed out for them.  I provide all students with the procedure because there are usually several steps and it saves time to have them typed and precut for them.  We all glue the procedure in on the inside, top right flap of the foldable.  I go over each step of the experiment explaining in detail and modeling for them what each step would look like.  By doing this, I am drawing attention to some of the variables they need to make sure they keep the same.  I am also calling on students who I notice are not paying attention to repeat steps for me so that I can check for understanding.  I try to set my students up for success, so that hopefully I will not have to correct actions during the experiment.  

After going over the procedure, I draw a data chart in the center of the foldable.  The data table for this experiment has 8 rows and 4 columns.  The headings for the columns are Beginning Temp, Ending Temp, and Difference.  The headings for the rows are the colors of envelopes.  

                                            

Identifying Variables:

After setting up the foldable, I direct students to record the variables on the blank page in their notebook to the left of the foldable.  We always use the page next to the foldable for recording variables, or record them on the front cover of the foldable.  The variables identified by my students are as follows:

  • Independent Variable - color of paper
  • Dependent Variable - temperature of each envelope 
  • Control Variables -   type of paper, the size of envelope, the location of the envelope, the thermometers used, and the time of day the envelopes are tested   

Explore

25 minutes

Conducting the Experiment:

After we set up the experiment, I pass out seven envelopes, one of each color, to each group, along with 7 thermometers.  Students divide up the envelopes so that each student in the group is responsible for checking the temperature of 2.  Having the students do this allows them to check the temperatures quickly because the longer they leave them sitting out, the more likely it is that the temperature will change making their data not reliable.  I explained this as we went over the procedure.  All students place a thermometer on top of each of their envelopes and let it sit for about 30 seconds before recording the temperature to ensure that it is not still changing.  I circulate to make sure everyone records the temperature in degrees Celsius.  This is also something I reviewed when going through the procedure.  

                                          

After recording the beginning temperatures, I instruct students to put their thermometers inside their envelopes and line up with their notebooks, pencil, and all materials for the experiment.  We go outside to a large sunny area and groups spread out.  All students lay their envelopes out in front of them, making sure there is no shade on the envelopes.  We wait for 15 minutes.  I track the time on a timer and will notify the whole group when it is time to check the temperature. 

                                           

While we are waiting, I pass out the materials for the s'mores.    

Making s'mores: 

I decided to make solar s'mores with the students for two reasons.  One reason is to fill time during the 15 minutes we are waiting to check the thermometers.  The other reason is to provide some foundational knowledge about how energy is stored in food for animals to use.  This is a major focus of this standard that will be covered later in the unit.  When I begin discussing the transfer of energy through an ecosystem and how animals use the energy they get from food, I can refer back to this activity.  

To begin the s'mores, I pass out a piece of black construction paper to each student.  I pass out one graham cracker to each student and ask them to break it in half.   I then pass out an individually wrapped miniature Hershey's bar to each student and ask them to place it on one of the graham cracker halves.  

                                              

As I pass out materials to students, I am asking questions to keep them focused on the science aspect of making the treat.  I ask questions such as: What is happening to the particles in the chocolate? (this is review from the unit on matter) Where is the energy coming from to heat up the chocolate? I explain that when energy is absorbed and stored in items such as food, it is called chemical energy.  The energy is stored in the food until a chemical reaction allows it to be released.  I ask What is going to react with the food once it is eaten? A student tell me their saliva.  I tell them that the saliva begins to break it down but energy is not released yet.  Once you swallow the food, what reacts with it?  A student tells me stomach acid which is correct.  

Final Steps: 

I pass out a marshmallow to each student to complete their s'more.  As I pass them out, I instruct students to remove their thermometers from the envelopes and record the new temperature.  I walk around to pass out a paper towel to each student and check that they have their final temperature recorded.  If they do, they get to eat their s'more.  I have them eat them outside as they do get messy.  The chocolate is melted and tends to run out when they begin eating.   

       

Wrap Up

10 minutes

Sharing Results:

Once s'mores are eaten, we go back inside to share results.  Groups first share data with each other as each group member only recorded the data for their 2 envelopes outside.  I give groups a few minutes to do the subtraction for each envelope so that they know the difference between the beginning temperature and ending temperature.  After each group has the data all recorded for their group, we go around to share our findings.  I ask each group to tell me the difference they found for each color.

All groups got the same results for which color heated up the most, the black.  The difference for the black envelope ranged from 18 to 24 degrees between groups.  I was happy to see that all groups found that the black heated up the most as this was the target for the activity, to prove the idea that black absorbs the most light, making it heat up the most.  Other than the black, there really wasn't any similarity in findings for the remaining colors.  Some groups found that red heated up the least, some found white, and some found green.  I was surprised at these results as I figured white would show the smallest change in temperature.  However, all colors other than black had very small differences between them for all groups.  The differences all ranged from 9 to 12 degrees so they were all very close to each other.