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ELECTRICAL INSTALLATION

Prepared by Tan Hee Chai

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Electricity is a term used to describe the energy produced (usually to perform work) when electrons are caused to directional (not randomly) flow from atom to atom.

In fact, the day-to-day products that we all benefit from, rely on the movement of electrons. This movement of electrons between atoms is called electrical current

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1.Electricity is a word used to describe the directional flow of electrons between atoms.

2.The directional movement of electrons between atoms is called electrical current.

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BASIC STRUCTURE OF MATTER

The Atom

All matter such as solids, liquids, and gases, is composed of atoms.

Therefore, the atom is considered to be the basic building block of matter

However, atoms are almost always grouped together with other atoms to form what is called a molecule. Only a few gases such as helium are composed of individual atoms as the structural unit.

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BASIC STRUCTURE OF MATTER

The Atom

Atoms are extremely small. The radius of a typical atom is on the order of 0.00000000001 meter and cannot be studied without very powerful microscopes.

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BASIC STRUCTURE OF MATTER

An incandescent light bulb

The woman pictured here is sitting at a scanning electron microscope which she will use to examine the light bulb closer.

Pictured here is the tungsten filament from inside the light bulb that was scanned. It is shown at 500 times its normal size.

Upon a closer scan, you can now see the oxide coating present on the tungsten filament which was orginally scanned from the light bulb. The filament is shown at 1950 times its orignal size.

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What is an atom composed of?

An atom is the smallest particle of any element that still retains the characteristics of that element. However, atoms consist of even smaller particles. Atoms consist of a central, dense nucleus that is surrounded by one or more lightweight negatively charged particles called electrons.

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What is an atom composed of?

The nucleus is made up of positively charged particles called protons and neutrons which are neutral.

An atom is held together by forces of attraction between the electrons and the protons.

The neutrons help to hold the protons together.

Protons and neutrons are believed to be made up of even smaller particles called quarks.

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Electric charge – Electrons

Electrons are the smallest and lightest of the particles in an atom.

Electrons are in constant motion as they circle around the nucleus of that atom.

Electrons are said to have a negative charge, which means that they seem to be surrounded by a kind of invisible force field. This is called an electrostatic field.

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Electric charge – Protons

Protons are much larger and heavier than electrons. Protons have a positive electrical charge. This positively charged electrostatic field is exactly the same strength as the electrostatic field in an electron, but it is opposite in polarity. Notice the negative electron and the positive proton have the same number of force field lines in each of the diagrams. In other words, the proton is exactly as positive as the electron is negative.

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Electric charge

These two electrons both have a negative charge so their lines

of force are repelled.

These two protons both have a positive charge so their lines of force

are repelled.

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Electric charge

The electron has a negative charge while the proton has a positive charge

which causes their lines of force to bend towards each other.

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Electric charge

Like charges repel, unlike charges attract

Two electrons will tend to repel each other because both have a negative electrical charge.

Two protons will also tend to repel each other because they both have a positive charge.

On the other hand, electrons and protons will be attracted to each other because of their unlike charges.

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Electric charge

Since the electron is much smaller and lighter than a proton, when they are attracted to each other due to their unlike charges, the electron usually does most of the moving.

This is because the protons have more mass and are harder to get moving.

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Electric charge

Although electrons are very small, their negative electrical charges are still quite strong.

Remember, the negative charge of an electron is the same as the positive electrical charge of the much larger in size proton.

This way the atom stays electrically balanced.

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Electric charge

Another important fact about the electrical charges of protons and electrons is that the farther away they are from each other, the less force their electric fields have on each other.

Similarly, the closer they are to each other, the more force they will experience from each other due to this invisible force field called an electric field.

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Maintaining electrical balance

Each basic element has a certain number of electrons and protons, which distinguishes each element from all other basic elements.

In most elements, the number of electrons is equal to the number of protons.

This maintains an electrical balance in the structure of atoms since protons and electrons have equal, but opposite electrostatic fields.

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Maintaining electrical balance

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Maintaining electrical balance

Pictured here is an atom of copper, which is much more complex than either an atom of hydrogen or helium.

The copper atom has 29 protons in its nucleus with 29 electrons orbiting the nucleus.

Notice that in the copper atom, the electrons are arranged in several layers called shells.

This is to graphically represent that the electrons are at different energy levels within the atom.

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Maintaining electrical balance

The energy of an electron is restricted to a few particular energy levels.

The energy is said to be quantized, meaning that it cannot vary continuously over a range, but instead is limited to certain values.

These energy levels or shells follow a very predictable pattern.

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Maintaining electrical balanceThe energy is said to be quantized, meaning that it cannot vary continuously over a range, but instead is limited to certain values.

These energy levels or shells follow a very predictable pattern. The closest shell to the nucleus can have up to 2 electrons.

The second shell from the nucleus can have up to 8 electrons. The third shell can have up to 18 electrons.

The fourth shell can have up to 32 electrons, and so on

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Maintaining electrical balance

Atoms can have this many electrons, but they do not have to have this many electrons in each shell.

The greater distance between the electrons in the outer shells and the protons in the nucleus mean the outer shell electrons experience less of a force of attraction to the nucleus than do the electron in the inner shells.

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What is the valence shell?

Notice that in the copper atom pictured below that the outside shell has only one electron.

This represents that the copper atom has one electron that is near the outer portion of the atom.

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What is the valence shell?

The outer shell of any atom is called the valence shell. When the valence electron in any atom gains sufficient energy from some outside force, it can break away from the parent atom and become what is called a free electron.

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Atoms with few electrons in their valence shell tend to have more free electrons since these valence electrons are more loosely bound to the nucleus.

In some materials like copper, the electrons are so loosely held by the atom and so close to the neighbouring atoms that it is difficult to determine which electron belongs to which atom.

Under these conditions, the valence or free electrons tend to drift randomly from one atom to its neighbouring atoms.

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Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount.

However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current.

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Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount.

However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current.

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Materials that have free electrons and allow electrical current to flow easily are called conductors.

Many materials do not have any free electrons.

Because of this fact, they do not tend to share their electrons very easily and do not make good conductors of electrical currents.

These materials are called insulators.

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The valence shell is the outer shell of the atom.

Some materials have a free electron in their valence shell and this electron can easily move from atom to atom.

The free electrons are responsible for electrical current.

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To be continued