033 – Electrostatic separation of grainy materials

Separation of salt and pepper  

Introduction to:  

Triboelectricity, charge, charge transfer, polarization, electrostatic force

Material:  

1. plastic spoon / plastic ruler / balloon.  
2. mixture of salt and pepper  
3. pepper  

+ woolen cloth / fur for rubbing (to generate the electrostatic charge)

Setup:  

• make a mixture of fine salt and finely ground pepper  
• generate electrostatic charge on the spoon by rubbing it  

Execution:  

• make a mixture of fine salt and finely ground pepper  
• generate electrostatic charge on the spoon by rubbing it     
• pass the spoon over the mixture  

Observation:  

the pepper is attracted to the spoon and sticks to it, the salt stays put  

Explanation:  

• The carbon-hydrogen chains in the pepper are polarized in the spoon’s electric field, as are the charges in the NaCl salt crystal. In the inhomogeneous field of the spoon there is an electrostatic attraction to both of them.
• The salt crystals, however, are much heavier and are therefore not lifted as easily as the pepper.