Electrostatic Deflection of a Water Stream

A thin stream of water falling from a cup can be deflected by bringing a charged rod near it. The demonstration shows how the polar nature of water molecules causes them to be attracted to charged objects.

1. Mount a plastic cup with a small hole in its base on a retort stand above a collection tray.
2. Fill the cup with water so that a thin, continuous stream falls into the tray.
3. Charge a plastic rod (or charging wand) by rubbing it with fur or wool.
4. Bring the charged rod close to the falling water stream without touching it.
5. Observe how the stream bends toward the rod due to the attraction of water molecules.

Deflection of water by a charged rod (NCPQ) - Dr Richard Walding:

Water deflection demonstration - SiouxScience:

📄 Electrostatic Deflection of Water Stream - The University of Melbourne: https://physics.unimelb.edu.au/lecture-demonstrations/electricity-and-magnetism/miscellaneous/el-18-electrostatic-deflection-of-water-stream

• Use different materials for charging (e.g., glass rod with silk, PVC rod with wool, balloon rubbed on hair) and compare effectiveness.
• Test other polar liquids (e.g., alcohol, vinegar) to see if they also deflect.
• Try non-polar liquids such as oil to show the absence of deflection.
• Vary the size of the hole in the cup to produce thinner or thicker water streams and compare the effect.

• Ensure water is collected safely in a tray to avoid spills on the floor.
• Keep electrical equipment away from the demonstration area.
• Handle the stand and cup carefully to prevent tipping.

• Why does the water stream bend toward the charged rod? (Because water molecules are polar; they align with and are attracted to the electric field.)
• Why does oil not show the same effect? (Oil molecules are non-polar and are not strongly influenced by an electric field.)
• What real-world applications use this principle? (Electrostatic precipitation, inkjet printing, and some spray technologies.)
• How would the deflection change if the water stream were larger in diameter? (A larger mass of water resists deflection, so the effect would be smaller.)