Equipment:

Source: One source for a fresnel lense is "Herbach and Rademan". They sell a 15" diameter lense for approximately $15.
1/800-848-8001

Lesson: Demonstrate the power available from sunlight. The fresnel lens captures a few square feet of sunlight and concentrates that energy to the size of a penny.

SAFETY WARNING!!!!!!

Looking at the melting penny is similar to looking directly into the sun. Eye damage can occur without any pain. Instruct everyone to look only for a second at a time and to then look away. We advise groups that if we see that people are staring at the penny, we will stop the demonstration. The person demonstrating will wear welder glasses and should also avoid staring directly at the penny.

Place the penny on the brick or tile and then hold the fresnel lens perpendicular to the sun. Adjust the distance between lens and penny until the focal point encompasses only the penny. The coin will begin to melt in less than 30 seconds. The penny shape will begin to distort and bubble. Remove lens and "stretch" penny with tweezers. Pour water over the penny to cool. Be sure penny is cool before giving to students.

It is helpful to tilt penny so that it is perpendicular to the sun.

Point out that a small fresnel lense is probably smaller than any window in their home and yet that small amount of sunlight contains an incredible amount of energy.

Every student will want the melted penny so we usually leave the penny(s) with the teacher.