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# The electric charge and the structure of matter

The static electricity is defined as electric charge at rest. We can only describe the properties of this charges and their behavior. The interactions between electric charge at rest can be observed by considering a plastic rod and a piece of fur. If the rods are charged by rubbing them with fur, the rods repel each other, also if the glass rods are rubbed with silk , the glass repel each other. It is found that charged plastic rods attract charged glass rod, and more so, the plastic rod and fur attract each other and the glass rod and silk attract each other too.

For example, Benjamin fracklin confirmed that there were two types of static  electric charge; positive and negative. The glass rods rubbed with silk become negatively charged. The electric charge is one of the attribute of the particles of which matter is made. Recall that matter is made of Atom.

Read also Electric current and Electric field

## The structure of atoms

The structure of Atom can be described in terms of three particles; Electrons, Protons and Neutron.

The electron is negatively charged while Proton is positively charged but Neutron has no charge.

### Mass of atom

Mass of electron is =9.1093897 x 10-31kg

Mass of Proton = 1.6726231 x 10 -27kg

Mass of Neutron =1.6749286 x 10-27kg

The mass of atom is concentrated at Nucleus. It is in the nucleus that Proton and Neutrons are found in atom. The mass of Proton is far greater than the mass of electron but the negative charge on electron has the same magnitude as the positive charge on proton. The neutral   atom has the equal numbers of Electron and Proton.

#### Ionization of atom.

If an atom gain electron it becomes negatively charged but if it loses electron it becomes positively charged. So the process of loosing or gaining electron by atom to become   either positively or negatively charged is called Ionization of atom.

Ion:    Atom that pose either negative or positive charge is called ion, Example, Sodium ion Na+ , Hydrogen ion H–  etc.

### How electric charge is produced

Charges are produced by the following:

By Friction: A glass acquires charges by friction when rubbed with silk cloth.

By contact: An object can gain charges by Contact, when charged body comes in contact with it.

By Electrostatic Induction: When a charge rod is brought near a body, it gives the body a charge of opposite sign, without losing any of its own charges. This process is called charging by Inductions

### Distributions of charges:

Note that charges on conductors are not evenly distributed, except on spherical surface. The charges are mostly concentrated at sharp point or very small area of the conductor.

## How to detect and test for charges.

The gold leaf Electroscope:  it is an instruments used in detecting and testing for small electric charges on a substance. It can also be used to determine if a charge is positive or negative.

Gold-leaf

### How to use Gold leaf electroscope

When a charged body is brought  the cap of electroscope , if the charge on the body is the same as the one on Gold leaf Electroscope, there will be increase in the divergence of the leaf, but if it is not the same there will be decrease in the divergence of the Leaf.

How to us Gold leaf electroscope to check if a body is a good conductor, Insulator of Semi-conductor

This is done by bringing the substance in contact with the cap of Gold leaf electroscope, if the substance is brought in contact with the cap and the leaf collapse, it shows that the substance is a good conductor, but if there is no charge in the divergence of the leaf it, means that ht substance is an Insulator. And if there is only slight charge in the divergence of the leaf, the substance is semi-conductor.

Conductor: it is a substance that allows the passage of heat or charges through it. Example, all metals are conductor, acid, etc.

Insulator: It is any substance that does not allow the passage of charges through it. Example, glass, dry wood, plastic etc.

Sem-conductor: this is either good conductor or an insulator.

### The resistivity of substances:

Resistivity of Conductor = 10-8

Resistivity of Insulator =104

Resistivity of Semi-conductor =10-1

### The effect of temperature on the resistivity of substance

The increase in temperature increases the resistivity of conductors, reduce the resistivity in Sem-conductor, but has no effect on insulator.