- All matter is composed of molecules which are made up of a combination of atoms. Atoms have a nucleus with electrons orbiting around it.
- The nucleus is composed of protons and neutrons (not shown). Most atoms have an equal number of electrons and protons.
- Electrons have a negative charge (-).
- Protons have a positive charge (+).
- Neutrons are neutral.
- The negative charge of the electrons is balanced by the positive charge of the protons.
- Electrons are bound in their orbit by the attraction of the protons.
- These are referred to as bound electrons.
- Electrons in the outer band can become free of their orbit by the application of some external force such as movement through a magnetic field, friction, or chemical action.
- These are referred to as free electrons.
- A free electron leaves a void which can be filled by an electron forced out of orbit from another atom.
- As free electrons move from one atom to the next an electron flow is produced.
- This is the basis of electricity.
Conductors, Insulators and Semiconductors
- An electric current is produced when free electrons move from one atom to the next.
- Materials that permit many electrons to move freely are called conductors.
- Copper, silver, aluminum, zinc, brass, and iron are considered good conductors.
- Copper is the most common material used for conduc- tors and is relatively inexpensive.
- Materials that allow few free electrons are called insulators.
- Materials such as plastic, rubber, glass, mica, and ceramic are good insulators.
- An electric cable is one example of how conductors and insulators are used.
- Electrons flow along a copper conductor to provide energy to an electric device such as a radio, lamp, or a motor.
- An insulator around the outside of the copper conductor is provided to keep electrons in the conductor.
- Semiconductor materials, such as silicon, can be used to manufacture devices that have characteristics of both conductors and insulators.
- Many semiconductor devices will act like a conductor when an external force is applied in one direction.
- When the external force is applied in the opposite direction, the semiconductor device will act like an insulator.
- This principle is the basis for transistors, diodes, and other solid-state electronic device.
Neutral state of an atom
- Elements are often identified by the number of electrons in orbit around the nucleus of the atoms making up the element and by the number of protons in the nucleus.
- A hydrogen atom, for example, has only one electron and one proton.
- An aluminum atom (illustrated) has 13 electrons and 13 protons.
- An atom with an equal number of electrons and protons is said to be electrically neutral.
Positive and negative charges
- Electrons in the outer band of an atom are easily displaced by the application of some external force.
- Electrons which are forced out of their orbits can result in a lack of electrons where they leave and an excess of electrons where they come to rest.
- The lack of electrons is called a positive charge because there are more protons than electrons.
- The excess of electrons has a negative charge.
- A positive or negative charge is caused by an absence or excess of electrons.
- The number of protons remains constant
Attraction and repulsion of electric charges
- The old saying, “opposites attract,” is true when dealing with electric charges. Charged bodies have an invisible electric field around them.
- When two like-charged bodies are brought together, their electric field will work to repel them.
- When two unlike-charged bodies are brought together, their electric field will work to attract them.
- The electric field around a charged body is represented by invisible lines of force.
- The invisible lines of force represent an invisible electrical field that causes the attraction and repulsion.
- Lines of force are shown leaving a body with a positive charge and entering a body with a negative charge.
- During the 18th century a French scientist, Charles A. Coulomb, studied fields of force that surround charged bodies.
- Coulomb discovered that charged bodies attract or repel each other with a force that is directly proportional to the product of the charges, and inversely proportional to the square of the distance between them.
- Today we call this Coulomb’s Law of Charges.
- Simply put, the force of attraction or repulsion depends on the strength of the charred bodies, and the distance between them.
1.Bunty B. Bommera
2.Dakshata U. Kamble