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Making Atoms Visible : Electroscope

Description: Easily create an electroscope to detect static electricity and radiation.

Grade Level
5-12

Disciplinary Core Ideas (DCI, NGSS)
5-PS1-1, MS-PS1-1, MS-PS1-4, HS-PS1-8, HS-PS4-2, HS-PS4-5

Time for Teacher Preparation
30-60 minutes – To gather materials and set-up

Activity Time:
30-60 minutes (1 Class Period)
Electroscope
Materials

Safety

Science and Engineering Practices (NGSS)

Cross Cutting Concepts (NGSS)

Objective
Make a simple instrument to detect static electricity and radiation.

Background
An electroscope is a very simple instrument that is used to detect the presence and magnitude of electric charge on a body such as static electricity. The type of electroscope detailed in this experiment is called a pith-ball electroscope. It was invented in 1754 by John Canton. The ball was originally made out of a spongy plant material called pith. Any lightweight nonconductive material, such as aluminum foil, can work as a pith ball. The pith ball is charged by touching it to a charged object. Since the ball is nonconductive and the electrons are not free to leave the atoms and move around the ball, when the charged ball is near a  positively charged body, or source, the negatively charged electrons are attracted to it and the ball moves towards the source. Conversely, a negatively charged source will repel the electrons, and therefore the ball. Electroscopes can also be used to detect ionizing radiation. In this case, the radiation ionizes the air to be more positively or negatively charged depending on the type of radiation, and the ball will either be attracted or repelled by the source. This is how electroscopes can be used for detecting x-rays, cosmic rays, and radiation from radioactive material.


Teacher Lesson Plan:

Traditional

  1. Lecture students on background
  2. Provide them with materials and procedure
  3. Provide balloons and radiation sources to test the electroscopes with

NGSS Guided Inquiry

  1. After students construct electroscopes, have them experiment with charged and neutral sources to experiment.
  2. Have students analyze radioactive sources with electroscopes.

Student Procedure

  1. Make two holes near the bottom of a foam cup on opposite sides.
  2. Push a plastic straw through the holes in the cup.
  3. Turn the cup upside down and glue it onto the bottom of an aluminum pie pan. Make sure that the cup is right at the edge so that the straw sticks out over it. If you don’t want to wait for the glue to dry, tape the cup to the pan.
  4. Cut a piece of thread about 8 inches long and tie a few knots in one end of the thread.
  5. Cut a one-inch square of aluminum foil. Use it to make a ball around the knots in the thread. The ball should be about the size of a marble. It should be just tight enough so it doesn’t fall off the thread.
  6. Tape the end of the thread to the straw so that the ball of foil hangs straight down from the straw, right next to the edge of the pan.
  7. Tape the straw to the cup so it doesn’t move around when you use the electroscope.
  8. To test the electroscope, create some static electricity. An easy way to create static is by rubbing a balloon on a foam plate. When you do this, you “charge” the plate, which means you cause a buildup of electrons on one side. Even though the plate is charged, the electrons don’t move because foam doesn’t conduct electrons.
  9. Once you’ve created some static electricity, place the electroscope on top of the foam plate. Be sure to hold the electroscope by the foam cup and not the aluminum pan, otherwise it won’t work. Electrons move easily through metal, so when you put the pie pan onto the foam plate, the electrons travel into the pan and the foil ball. When the electroscope detects static electricity, the foil ball pushes out from the pan.
  10. Try charging different objects, like a comb or ruler, with static electricity. Test them on the electroscope and record your results on the data sheet.

Data Collection
Students should record which objects hold a charge and which do not

Post Discussion/Effective Teaching Strategies

Questions

  1. Which objects hold an electric charge? Which don’t?
  2. Why is the ball attracted or repelled by different objects?
  3. How is using an electroscope similar to testing the charge of a balloon with your hair?
  4. How is the electroscope able to detect radioactivity?

Assessment Ideas
Have students use electroscopes to discern between radioactive sources and nonradioactive sources.

Differentiated Learning/Enrichment
Have students compare radioactivity of different sources.

Enrichment Question

  1. Why did John Canton invent the first electroscope and what did he use it for?

Further Resources
For additional background information:
Electroscope: http://science.howstuffworks.com/electroscopeinfo.htm
Electroscope: http://www.gdr.org/radiationdetectors.htm

 

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