Summary

In this demonstration, the teacher will pop popcorn using three different methods (a hot plate, a microwave, and an air popper) so that the students can experience and investigate three types of heat energy transfer: convection, conduction, and radiation.

Grade Level

Middle School

Objectives

By the end of this demonstration, students should be able to

• Compare and contrast the three types of heat transfer: convection, conduction, and radiation.

Chemistry Topics

This demonstration supports students’ understanding of

• Energy
• Heat
• Heat Transfer
• Convection
• Radiation
• Conduction

Time

Teacher Preparation: 30-60 minutes

Lesson: 45-60 minutes

Materials

• Microwave
• Air popper
• Hot plate
• Small pan and lid
• Microwave popcorn (1 bag)
• Popcorn kernels (1 bag)
• Vegetable oil (1 Tbsp.)
• 3 small microwave-safe bowls
• 1-3 electrical outlets
• Paper bowls for students to eat the popcorn (Optional: if you are going to allow this)
• 1 stopwatch per student

Safety

• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.

Teacher Notes

• Background information:
  • The hot plate is the source of conduction heat
  • The microwave is the course of radiation heat
  • The air Popper is the source of convection heat
• Hints for a successful demo:
  • If you are doing this demonstration in a class period that is 45 minutes-1 hour, I recommend that you have all three devices running at same time. Explain the heat sources to the student to allow enough time for the demo to be completed and the students finish their activities.
  • The students should complete a compare/contrast Venn diagram as a final assessment.
  • Length of class can dictate how quickly the demo must proceed.
  • Allow the students to come up in small groups to view what is occurring up close.
  • The popcorn produced in the radiation and convection demos should be appropriate to share with the students; however the conduction popcorn will be greasy and will not produce a good quality for consuming.
• Demo procedures:
  • Conduction:
    1. Heat a hot plate and place a pan with lid on the heat source.
    2. Add 1 tablespoon of oil to the pan.
    3. When the pan is heated and the oil is hot, add approximately 15 popcorn kernels and close the lid.
    4. Once the kernels begin to pop, remove the pan from the heat source. Show the class what has occurred.
    5. Optionally, you could do this without the lid and the popcorn will pop out of the pan. However, keep in mind that the oil and popcorn will be very hot.
  • Radiation:
    1. Pop the popcorn in the microwave bag by following the instruction on the box of popcorn.
    2. Be sure to follow the instruction on the box closely so that the popcorn does not burn.
    3. Show the class what has occurred.
  • Convection:
    1. Fill the air popper using the instructions for the popper or fill the inside of the popper to the line with kernels.
    2. Make sure that the lid is in place and a heat resistant bowl is below the opening.
    3. Plug in the unit.
    4. The kernels will be bounced around the inside of the popper by the hot air until they are heated to popping.
    5. Once the kernels are finished popping, show the class what has occurred.