When high energy radiation strikes the Earth from space, it’s called cosmic rays. To be accurate, a cosmic ray is not like a ray of sunshine, but rather is a super-fast particle slinging through space. Think of throwing a grain of sand at a 100 mph… and that’s what we call a ‘cosmic ray’. Build your own electroscope with this video!

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  • Clean glass jar with a lid
  • Wire coat hanger and sand paper
  • Aluminum foil
  • Vice grips or a hacksaw
  • Scissors
  • Balloon or other object to create a static charge
  • Hot glue gun (optional)


Download Student Worksheet & Exercises

Troubleshooting: This device is also known as an electroscope, and its job is to detect static charges, whether positive or negative.  The easiest way to make sure your electroscope is working is to rub your head with a balloon and bring it near the foil ball on top – the foil “leaves” inside the jar should spread apart into a V-shape.


  1. How does this detector work?
  2. Do all particles leave the same trail?
  3. What happens when the magnet is brought close to the jar?


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One Response to “Cosmic Ray Detector”

  1. this is so good