011 – Electrostatic deflection

Bending a water stream due to electrostatic forces 

Introduction to:   

Electric dipole, force on electric charge, electric field, electrostatic forces 

Material:   

• Faucet with thin stream of water  
• Plastic comb / plastic spoon / balloon   

+ Material for rubbing (woolen cloth, fur).  

Setup:  

• charge the spoon electrostatically by rubbing it vigorously against the material 
• Open the faucet to create a thin stream of water 

Execution:  

• hold the spoon near the water 
• hold the spoon into the water

Observation:  

• the water stream is curved towards the spoon
• When the water comes into direct contact with the spoon, the curvature decreases.  

Tips:  

Freshly washed, dry hair is also a good material for rubbing  

Explanation:  

• Water molecules have a permanent electric dipole moment. In the electric field of the charged spoon, molecules in the water stream align themselves in the direction of the field and experience electrostatic attraction in this inhomogeneous electric field.  
• When in contact with the water, the electric charges flow off the spoon, the strength of the electrostatic field decreases. 

Didactic potential:  

Simple demonstration of electrostatic forces