015 – Detecting Electrical Charge

Radio as a charge detector  

Antenna as lightning rod  

 

Introduction to:  

  • Triboelectricity  
  • Electric charge  

 

Material:  

  • Transistor radio with external antenna  

Friction mecanism:

  • Plastic rod (e.g. PVC pipe) / ruler made of plastic  
  • Woolen cloth (e.g. scarf, sweater) or sheepskin  

Setup: 

  • Tune the radio to a frequency without a transmitter.  
  • Turn the speaker up to full volume.  
  • Charge the plastic rod electrically with the woolen cloth.  

Execution:  

  1. Sew the plastic rod of the antenna close. 
  2. Strip off the plastic rod on the antenna.

Observation:  

  1. The noise in the speaker becomes weaker. 
  2. “Cracking noises” can be heard from the loudspeaker. 

Explication:  

  • The friction between the plastic rod and the woolen cloth separates electrical charges, so that the plastic rod becomes electrically charged.  
  1. The charges on the plastic rod create an electric field. This interferes with the electromagnetic waves that the radio receives. 
  2. The potential difference between the plastic rod and the antenna is a few thousand volts and leads to flashovers when touched. These are converted into “cracking sounds” by the radio. In this process, the charges flow from the plastic rod via the antenna to Earth. 

Note:  

  • Tests with frictional electricity do not work in humid air or with damp material.