Without an electrical charge the foil strips hang freely.
By Patrick Mahony
Have you ever been surprised by a static shock? This clever device can measure electrical charge!
When you rub the balloon against something woolly, some of the electrons from the atoms in the fabric are transferred onto the balloon. These extra electrons give the balloon an overall negative charge. The rubber of the balloon is an insulator. This means the electrons can’t move very easily through the rubber, so the charge stays put.
The negative charge means there is an electric field around the charged surface of the balloon. This field can affect other charged particles.
When the charged balloon is moved close to the jar, the electric field passes through the glass. The aluminium foil strips are conductors. Unlike insulators, conductors are materials that electrons can move through readily. The electrons in the metal foil are repelled by the electric field on the balloon and move away. This creates an imbalance of charge within the metal strips.
If the two strips end up with different charges – one positive and one negative – they will attract each other. If they have the same charge – both positive or both negative – they will push each other away. The movement of the strips shows that a net electric charge (more negative, or more positive) is present. An instrument used to detect and measure electric charge is called an electroscope.
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7 March, 2022 at 3:27 pm
Thank you for these instructions. I am not sure if the humidity will allow this to work, but I want us to try it.