When we rub a glass rod with a silk cloth, both the glass rod and the silk cloth become charged. The charges are transferred between the two during the process of rubbing.
But contact is not necessary for charges to be transferred. We can understand this with the help of an instrument called an electroscope.
What is an Electroscope?
An electroscope is a simple instrument that is used to detect whether an object is carrying charge or not.
Parts of an Electroscope
It has a metallic ball terminal at the top which is attached to a metal rod. There are two strips of aluminium foils, hanging freely with their one end fixed to the rod. The whole set up, except the metallic ball, is enclosed in a glass container as seen in the diagram below.
How does an electroscope work?
If any charged object is brought near the metal sphere in its neutral state, the two metal foils go away from each other.
The charge from the object is transferred to the sphere and reaches the foils through the metal rod. Both the aluminium foils have the same charge on their surfaces and hence they repel each other.
For example, if the metal sphere is touched with a charged glass rod and let go, the metal foils move away from each other.
There is no contact between the glass rod and aluminium foils. Yet the charge is transferred.
What is Discharging an Object?
When excess charges leave a charged object, making it return to its original, neutral state, it is called Discharging.
For example, when we touch the metallic ball of the electroscope with our hand, the charged aluminium foils get back to the position they were before being charged. That is because our body being a good conductor transfers the charge to the earth. This process is also known as Earthing.
What is Earthing?
It is defined as the process of transferring charge from a charged object to the earth.
Applications of earthing
Lightning that strikes a building can destroy it in unexpected ways. Earthing provided to the buildings protects it by carrying the charge from the lightning to the earth and keeps the building safe. This is one of the many applications of earthing.
Summary
| Electroscope | A simple instrument that is used to detect whether an object is carrying charge or not |
| Discharging an Object | When excess charges leave a charged object, making it return to its original, neutral state |
| Earthing | The process of transferring of charge from a charged object to the earth |
Also Check: