Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Bending of Water Stream due to Electrostatic Charges

Objective

To demonstrate electrostatic attraction due to induced charge.

Introduction

The water molecule is neutral but has non-zero dipole moment. A stream of water is easily attracted by a charged body due to non-zero dipole moment of the water molecules. We demonstrate this phenomenon in this experiment.

Apparatus

A plastic bottle, a plastic scale or comb

Procedure

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Make a small hole at the bottom of a water bottle. Make sure that a clear stream of water comes out when bottle is filled with water. The hole should not be too small or too big. Rub a plastic scale (or comb) with cloth and bring it close to the stream (near the top portion). You will observe that stream bends towards the scale. This demo shows the concept of induced charges (water is a polar molecule) and electrostatic attraction.

Note

There are claims that polar nature of water is not the right explanation for bending of water stream. The stream is bent because of presence of ions in tap water. We need to do this experiment with distilled water to confirm this.