ELECTROSTATICS

 This is a branch of science that deals with the study of charges at rest. We have discussed charges on motion under the topic Current Electricity.

All bodies consist of charges. It is either a body is positive, negative or neutral.

A body is said to be positively charged if it contains excess positive charges or it has deficiency in negative charges.

A body is said to be negatively charged if it contains excess negative charges or it has deficiency in positive charges.

A body is said to electrically neutral if it has equal number of positive and negative charges.

A body can be charged through three methods. They are

1. By Friction
2. By Contact
3. By Induction

Charging by Friction

When you rub two neutral bodies together, they are likely to get opposite charges. For example, When we rub ebonite rod with fur, the ebonite rod will possess negative charges while the fur will possess positive charges.

When we rob glass with silk, the glass will possess positive charges while the silk will possess negative charges. This method is called charging by Friction.

Charging by Contact

In this method, the body to be charged is placed in direct contact with an already charged body. During Contact, charges will flow from the charged body to the uncharged body until the two bodies have the same magnitude of charges i.e they are now at the same potential.

After separation, the charges in the body are now distributed uniformly in the body.

During the process of charging a body by contact, the bodies are placed on an Insulating stand to prevent flow of charges into the body from the earth or away from the body down to the earth.

Below are diagrams to explain Charging by contact.

• Before contact

• During Charging

• After Separation

Note: Charges can only flow from one body to another if there is an evidence of potential difference( i.e the number of charges in them are different).

Charging by Induction

This method is used to produce charges of opposite signs. For example, a body can be charged negatively through induction by using a positively charged rod. A body can also be charged positively by using a negatively charged rod.

The following steps are used for a charging a body negatively through induction.

• Bring a positive charged rod beside the body

Negative charges in the body are attracted towards the positively charged rod while the positive charges are repelled.

• Earthing is carried out by touching the body

Negative charges will flow from the earth through the finger into the body and neutralize the positive charges.

• The finger is removed

• The positive charge rod is then removed

Gold- Leaf Electroscope

This device is used for detecting the nature of charges on a body. It consist of metal cap, thin conducting rod, glass window and a gold leaf.

          Gold- Leaf Electroscope

The Electroscope must be first be charged before it can be used.

If a body is placed on the metal cap, and the leaves diverges (open up), the implication is that the electroscope and the body have identical charges.

If a body is placed on the metal cap, and the leaves collapses ( close up), the implication is that the electroscope and the body have opposite charges.

If a body is placed on the metal cap, and the leaves remain unchanged, it means that the body is neutral.

Some other devices we need to know thier functions

• Electrophorus: This is use for producing charges of one kind in large quantity.
• Proof plane: This is use for transferring charges from one body to another.

Exercises

1. Aluminium is sometimes used as the leaf of an electroscope because it (a) is a good insulator (b) is a light material (c) is a good conductor (d) can be converted into thin sheets
2. When a negatively charged rod is brought near the cap of a negatively charged gold-leaf electroscope, the leaves will (a) collapse (b) become positively charged (c) negatively charged (d) diverge more
3. When a positively charged rod is brought nearer the cap of a positively charged electroscope, the leaves divergence will (a) converge (b) be induced (c) diverge (d) remain constant
4. If negative charges are induced on an electroscope and a positively charged rod is brought near the cap of the electroscope, the leaves will (a) become negatively charged (b) become positively charged (c) open further (d) close up

Answer the questions and write your answers in the comment section below