Introduction: Transfer of Heat Through Conduction, Convection and Radiation

Introduction: Transfer of heat through conduction, convection and radiation

Thermal energy can simply be described as a flow of energy, or a means of energy that is moving from one system or state to another. As the energy moves from one state to another, a difference in temperature will occur. This difference in temperature is noted as the thermal energy. Thermal energy can be transferred by conduction, convection current and radiation. The transfer of energy can be studied through the skills of experimentation. The transfer of energy drives natural processes such as regulating geothermal energy contained below the earth and global warming due to increased amount of radiant energy reaching the surface of the earth.

The concept presentation will identify some common misconceptions found in the Grade 7 Heat Unit, subunit: Transfer of thermal energy through the process of conduction, convection and radiation. Using experimentation, class discussions, and demonstrations these misconceptions will be solved by the end of the presentation. Further the presentation will also provide Ontario curriculum expectations that link the grade 7 heat unit with grade 9 Earth and space: Climate Change unit.

Grade 7: Heat Unit

Fundamental concept: Energy transfer

Big idea: Heat is a form of energy that can be transformed and transferred. These processes can be explained using the particle theory of matter.

Overall Expectations

2. Investigate ways in which heat changes substances, and describe how heat is transferred.

3. Demonstrate an understanding of heat as a form of energy that is associated with the movement of particles and essential to many processes within the earth’s systems.

Specific Expectations

3.1 Use the particle theory to compare how heat affects the motion of particles in solids, liquids and gases.

3.3 Use particle theory to explain the effects of heat on volume of solids, liquids and gases.

3.4Explain how heat is transmitted through conduction.

3.5 Explain how heat is transmitted through convection.

3.6 Explain how heat is transmitted through radiant energy.

2.4 Use scientific inquiry and experimentation skills to investigate heat transfer through conduction, convection and radiant energy.

2.5 Use appropriate science and technology vocabulary, including heat, temperature, conduction, convection and radiation in oral and written communication.

3.7 Describe the role of radiation in heating and cooling the earth, and explain how greenhouse gases affect the transmission of radiated heat through the atmosphere.

Grade 9 Earth and Space: Climate Change

Overall expectations:

D1. Analyze some of the effects of climate change around the world, and assess the effectiveness of initiatives that attempt to address the issue of climate change.

Specific Expectations:

D3.2 Describe and explain heat transfer in the hydrosphere and atmosphere and its effects on air and water currents.

D3.3 Describe the natural green house effect.

Common Misconceptions

1.  Particles get bigger when heated

In solids, the particles are arranged in a regular pattern, closely packed together. They attract each other with a strong force. The particles of matter are always moving. Since they cannot change places in a solid, they simply vibrate when thermal energy is added. As they vibrate more, they bang into the ones next to them. This makes them vibrate more than they were at first. Eventually all of the particles are vibrating faster as thermal energy is being transferred or conducted by the object.

Experiment: Use the ball and ring experiment to test for expansion of particles when thermal energy is transferred through conduction. Ball and ring experiment to explain conduction.

The sequence used to heat up the objects

1.  RT ball and RT ring =

2.  Hot ball and RT ring =

3.  Hot ball and hot ring =

4.  RT ball and hot ring =

Explain the observations in terms of the motion of the metal particles in the ball and ring.

Make statements describing the sizes in relation to the ball and ring at different temperatures. (RT= Room Temperature)

2.  Convection current forms only when gas or liquid is boiled.

Gas and fluid particles do not have to be boiling to go through the process of convection current. Convection is the transfer of thermal energy by the actual movement of the warm material. When fluid or gas particles are warm with thermal energy, they expand and become less dense in mass. They rise up through the cooler, dense particles. As the water particles cool, it increases its density, which causes it to sink back down to the bottom. This up and down movement eventually transfers thermal energy to all of the particles. The continual cycling called convection current. However cooling a fluid from above will also produce convection current.

Following experiment can be performed to further demonstrate this point.

·  Plastic container with RT water supported by four Styrofoam cup.

·  Place a drop of red food coloring at the bottom of the water.

·  Place blue coloured ice cubes at the top

·  Place a cup of hot water at the bottom of the food coloring.

·  Observe what happens and discuss it in class.

3.  Gases, liquids and solids heat up at the same rate and release thermal energy at the same rate.

Formation of sea breeze: Large areas of land heat up more quickly than adjacent sea water (water has a large heat capacity and is a good conductor of heat). Air near the land surface is heated by radiation and conduction, expands and begins to rise, being lighter than the surrounding air. This is convection. To replace the rising air, cooler air is drawn in from the surface of the sea. This is called a sea breeze, and can offer a pleasant cooling influence on hot summer afternoons when further inland the heat may become oppressive. Air above the sea sinks and is again pulled in over the land. The full sea breeze circulation is show in the figure.1.

Formation of land breeze: Since the sea breeze owes its existence to the enhanced heating of the land under the sun, it follows that at night, when the land cools faster than the sea, a land breeze may develop. The warmer air over the sea then rises, pulling out the colder air over the land to generate a land breeze Figure.2.

Experiment: Demonstrations from YouTube and be used as a teaching tool.

4.  All black objects are good insulators.

Radiant energy travels through empty space. For a black coloured object to become an insulator of thermal energy it as to be left out side in direct view of sunlight or near a roaring flame but not touching the flame. A black coloured object left under room temperature conditions will not turn into an insulator of thermal energy. Ex: A plastic bottle filled with warm water and wrapped in black cloth will not be a good insulator of thermal energy.

Experiment Part A: Are all dark objects good insulators of thermal energy.

1. Have students make data tables to record the time and temperature of the three experimental pie pans. Examples:

Heating Cycle
Surface material / Start time / Start temp. / Temperature each minute
1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10

2. Re-draw the table for the cooling cycle.

3. Fill the pie pans to the same level, one with dark soil, one with light sand, and one with water.

4. Place the pie pans on a table or desk and position the lamp about 12 inches above them.

5.  Place a thermometer into each pie pan, securing it so it measures the temperature just under the surface of the substance in the pan.

6.  Record the starting temperatures on the data table.

7.  Turn on the lamp and record the temperature of each substance every minute for ten minutes.

Part B Repeat the entire procedure but this time remove the lamp for the entire time the experiment is carried out. Discuss the variations in the results.

Placement of the concept within the unit

Chapter 7 / Chapter 8 / Chapter 9
Warmth and coldness / Thermal energy transfer / Energy sources
Explaining hot and cold / Investigation: transfer of energy through a substance. / Conventional energy sources
Kinetic energy, heat , temperature / Conduction / Global warming
Investigation: contraction expansion / Conduction and geological process / Alternative energy sources; wind, solar, geothermal, biofeul
Living with thermal expansion and contraction / Convection / summary
Convection in the Environment
Radiation
Managing transfer of thermal energy

Place in the Curriculum

The students will be taught the heat unit in term three. This way they would have already done the particle theory of matter and the structures of the three states of matter in term two in the pure substance and mixtures unit. This topic will further help the students to understand scientific concepts in the Earth and Space unit in grade 9. Heat transfer, geothermal conduction, weather patterns, ocean currents, global warming and green house gas circulation is studied in the grade 7 geography curriculum. In the grade 8 Water and Fluids science units these concepts are further enhanced and experimented on.

Five day lesson plan

Day / Lesson sequence and teaching ideas / Curriculum expectation / Advance preparations/ materials / Assessment (A) Evaluation (E) / Learning styles (LS) / Multiple intelligence (MI) / Differentiated Instruction / Societal implications
Practical application
1 / Review prior knowledge of particle theory of matter, changes of states, characteristics of solids, liquids and gases.
KWL chart. Discuss with elbow partner
Power point presentation
Experiment: Kinetic energy, heat, temperature, expansion and contraction of particles. / 1.1, 2.1, 2.2, 2.5, 2.6
3.1, 3.2, 3.3 / Laptop, LCD, Particle theory program, PowerPoint on three states of matter.
KWL chart photocopies.
Equipments for experiment: Beaker, ice cubes, volumetric flask, balloon, tap water and hot water.
Provide a glossary of vocabulary terms. / Informal question and answer. (A)
Think pair and share (A)
KWL chart (A)
Formal lab report (E) / (LS) Kinesthetic, auditory, visual, tactile learners.
(MS) Logical, visual, intrapersonal, interpersonal, verbal / Use the chapter opener pictures from the text book.
Encourage discussions on methods of energy transfer.
Chart paper divided into solids, liquids and gases.
Groups write on information on stickies and put stick on the chart paper. / Relate the concept to the function of steam engines.
Dangers of rising sea levels due to global warming.
2 / Thermal energy transfer: Conduct an investigation to demonstrate conduction in solids.
Power point presentation.
Experiment: ball and ring.
Five point conductor meter with wax on each of the metals to test best heat conductor. / 1.1, 2.1, 2.5, 2.6, 3.1, 3.2, 3.4 / Equipment: Ring and ball, candle, five point conductor meter, matches, results handout / Informal quest and Answer (A)
Formal lab report (E) / (LS) Kinesthetic, auditory, visual, tactile learners.
(MS) Logical, visual, intrapersonal, interpersonal, verbal / Use visuals from the text book and Youtube to relate the message of heat conduction.
Create vocabulary cards with a word on one side and their version of the meaning. Students can use their native language to rephrase the meaning of the word.
Give complete procedure for the lab.
Graphic organizer to complete the lab report write up. / Discuss the uses of some plastics as thermal energy conductors in the electronics industry.
3 / Thermal energy transfer: Conduct an investigation to demonstrate convection current in liquids and gases
Power point presentation.
Youtube presentation on sea breeze formation demonstrates convection current in gases and liquids.
Experiment: Use food coloring, water, plastic container and hot water, ice cubes to show convection current in liquids. / 2.1, 2.4, 2.5, 2.6, 3.1, 3.5, / LCD, computer, worksheets
Equipment: blue and red food coloring, large plastic container, five Styrofoam cups, pipette, hot water, room temperature water ice cubes.
Results collection handout. / Informal quest and Answer (A)
Formal lab report (E) / (LS) Kinesthetic, auditory, visual, tactile learners.
(MS) Logical, visual, intrapersonal, interpersonal, verbal / Venn diagram to compare convection and conduction.
Review terms “rise,” “sink, “expand” and “contract”
Use everyday illustrations and phenomena to demonstrate these points.
Give ELL students plenty of time to discuss these words in their table groups.
Give complete procedure for the lab.
Graphic organizer to complete the lab report write up. / Discuss how convection can be used to explain the process of releasing smoke through a chimney.
Formation of igneous rock (geography)
4 / Thermal energy transfer: Conduct an investigation to demonstrate radiation.
Power point presentation.
Experiment: three Petri dishes with two different coloured soil and water. A heat lamp and thermometer.
Recording sheet. / 1.1, 2.1, 2.4, 2.5, 2.6, 3.6. / LCD, computer, worksheets
Equipment: three Petri dishes, two different coloured soil samples, water sample, heat lamp and thermometers. / Informal quest and Answer (A)
Formal lab report (E) / (LS) Kinesthetic, auditory, visual, tactile learners.
(MS) Logical, visual, intrapersonal, interpersonal, verbal / Identify that radiation is synonym for “transfer of radiant energy” and “radiant energy”.
Give complete procedure for the lab.
Graphic organizer to complete the lab report write up. / Discuss the theory behind using certain coloured clothing in countries that receive high amounts of sunlight.
The purpose of using certain materials by fire fighters when fighting extreme fires.
5 / Reviewing the concepts learned
Divide class into groups of 5:
Create Talbots on the concepts.
Create a story by each person saying a sentence based on the concepts.
Work in pairs and play “Show it in action”. Student A will start with a short sentence based on the concept. Student B will show the action for it and say another sentence. Student A will do that action and so on.
Group discussions on some issues formulated during the source of the five days.
Talk about methods used to control the transfer of thermal energy.
Design challenge is introduced: Building a thermos using a 2L pop bottle which will keep water above 75 degrees for two hours. / 2.1, 2.5, 2.6, / For the review activities students need to be in groups of 5 or in pairs.
Classroom space or hallway is provided.
Issues written on cards and chart paper.
Students bring materials to build their thermos. / Informal question and Answer, Class discussion, group discussion, presentation to class (A)
Design challenge: Formal lab report, and end product (E) / (LS) Kinesthetic, auditory, visual, tactile learners.
(MS) Logical, visual, intrapersonal, interpersonal, verbal / Draw three point Venn diagram to review radiation, convection, conduction.
Use diagrams from texts and YouTube to facilitate concepts.
Encourage students to participate in think pare and share.
Allows the silent students to talk to a partner.
Provide chart paper to table groups and stickies for the groups to put information in the appropriate columns.
When presenting allow ELL and Sp.Ed student to re-read what they have previously written. / Design challenge will allow students to understand the various forms of insulation material used in the industry.
Working in teams.
Responsibility.
The drama component will allow for student creativity.

Safety considerations: