Technology Electricity: Power, Energy, AC/DC, and Practical Examples

The Electric Charge

Electric charge is a property that all objects possess and is responsible for electrical phenomena.

There are two types of electric charge: POSITIVE CHARGE and NEGATIVE CHARGE · Like charges repel each other. . Unlike charges attract each other.

+ + I I + I To understand the electrical phenomena of attraction and repulsion, we must remember that all matter is made up of ATOMS

While its name originally referred to a particle that couldn't be divided any more (the smallest thing possible) we now know that each atom is generally made up of smaller particles, each of which have an electrical charge.

Basic Structure of an Atom

ATOMS are the basic building blocks of matter comprised of smaller particles:

Electron Neutron (blue) in nucleus Path of Electrons Proton (red) in nucleus

• Electrons, which have negative charge and are responsible for electric forces and interactions.
• Protons, which have positive charge.
• Neutrons, which don't have a charge and help in keeping protons together.

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Types of Electricity

There are two ways to generate the magical thing call electricity.

STATIC ELECTRICITY CURRENT ELECTRICITY

Static Electricity

In general, matter is neutral (it doesn't have an electric charge). This means that the number of negative charges (electrons) is the same as the number of positive charges (protons).

But all objects can become positively or negatively charged when there is movement of electrons from one material to another.

_A positively charged object has less negatives than positives charges. _A negatively charged object has more negatives than positives charges.

ONLY NEGATIVE CHARGES MOVE POSITIVE CHARGES NEVER MOVE

That's exactly what static electricity is. Static electricity is the build-up of an electrical charge on the surface of an object.

The reason that it's called static electricity is because the charges stay in one area for some time and don't flow or move to a different area, they "jump". The charges are at rest.

Electrostatic Series

Table 1 Electrostatic Series Material Charge tendency human skin + rabbit fur acetate glass (weaker tendency to gain electrons) human hair nylon wool cat fur silk paper cotton wood amber rubber balloon vinyl polyester ebonite -

Electrostatic Series is a list that ranks object's ability to take negative charges.

Current Electricity

Just as water can flow through a tube, electrons can move through certain materials and create an electric current.

An ELECTRIC CURRENT is a continuous movement of electrons through certain materials.

Materials can be classified depending on its ability to conduct electricity.

TECHNOLOGY | 3º ESO | ELECTRICITY c by Rocío Yuste | Page 3 out of 16 (stronger tendency to gain electrons)Some materials let electricity pass through them easily. These materials are known as electrical CONDUCTORS.

Many metals, such as copper, iron and steel, are good electrical conductors. That is why the parts of electrical objects that need to let electricity pass through are always made of metal.

Metal is used in plugs to allow electricity to transfer from the wall socket, through the plug, and into a device such as a radio or TV.

In a light bulb, the metal filament conducts electricity and causes the light bulb to light up.

Common Conductors and Insulators

Table 1 Common Conductors Good conductors Fair conductors silver graphite (carbon) copper nichrome gold the human body aluminum damp skin magnesium acid solutions tungsten salt water nickel Earth mercury water vapour in air platinum silicon iron germanium

Some materials do not allow electricity to pass through them. These materials are known as electrical INSULATORS.

Plastic, wood, glass and rubber are good electrical insulators. That is why they are used to cover materials that carry electricity.

The plastic covering those surrounds wires is an electrical insulator. It stops you from getting an electrical shock.

Insulators has weaker tendency to lose electrons.

Table 2 Common Insulators Good insulators oil plastic fur wood silk paper wool wax rubber ebonite porcelain, glass pure water

Static Electricity vs Current Electricity

Static Electricity Current Electricity It is a type of electricity that is built upon the surface of a substance. It is a type of electricity that results due to the flow of electrons across a conductor. Static electricity is induced due to the movement of negative charges from one object to another. Current electricity is induced due to the movement of electrons. Doesn't induce a magnetic field Induces a magnetic field Exists for a short period of time Exists for an extended period of time This type of electricity develops both in insulators and conductors. This type of electricity develops in conductors only. Gold leaf electroscope measures static electricity. Analog and digital meters measure current electricity. Lightning strokes are a result of static electricity. The current electricity is used to run our daily appliances.

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Electricity in Daily Life

We use electricity constantly in our daily lives. Electricity is one of our most important types of energy that we use.

Electricity is a type of energy that can build up in one place or flow from one place to another place.

This energy can be transformed into other types of energy that we can use, such as:

CC 0000 HEAT LIGHT MOTION

Electric Circuits

An electric circuit is a set of connected components through which an electric current flows.

Before the discovery of the electron, scientists assumed that current was due to positively- charged particles moving from the positive side of the battery around a circuit to the negative side. This way of representing the direction of current is called CONVENTIONAL CURRENT.

+ Conventional Current + Electron Flow I

It is now known that charge is carried by electrons, flowing from the negative to the positive side of the battery. This is call ELECTRON FLOW.

Electrical engineers use CONVENTIONAL FLOW because it was used at the first place and switching to ELECTRON FLOW now will case confusion.

Basic Elements of an Electric Circuit

The basic elements of an electric circuit are:

• GENERATORS
• CONDUCTORS
• RECEPTORS
• CONTROL COMPONENTS
• PROTECTION COMPONENTS

Light bulb Switch Resistor Battery

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Generators

To generate and maintain an electric current, we need a device that produces the energy necessary for electrons to move. This device is called a GENERATOR.

• BATTERIES: they use chemical processes to generate the electric current.
• ALTERNATORS OR DYNAMOS: they transform motion into an electric current with the use of a magnet.
• PHOTOVOLTAIC SOLAR CELLS: they convert the energy of sun light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
• HYDROGEN CELLS: they produce energy from oxygen in the air and hydrogen.

Conductors

The elements that join all the components of a circuit and allow the flow of current are the CONDUCTORS. They can be cables or wires.

Basic differences between the cables and wires: The basic key difference between cables and wires is that a wire is a single conductor whereas a cable is a group of conductors. But the conductors of both wires and cables are made of a common material either copper or aluminum.

Control Components

The elements that direct or interrupt the flow of the electric current are the CONTROL COMPONENTS. The most common types are:

• A switch (a 2-way switch): this has two positions. One allow the flow of electric current, the other stop it.
• A 3-way switch: this has two outputs, so it communicates with two different circuits, allowing the current to go one way or the other depending on its position.
• A push button: this is similar to a 2-way switch, but it has a fixed position which changes when pressed. It returns to this position when we let it go.

Receptors

The elements that transform the electrical energy that they receive into another type of useful energy are the RECEPTORS.

The electrons leave the generator, taking the energy with them and move round the circuit, through the conductors, until they get back to the opposite terminal.

Receptor Energy Effect Electric resistors thermal or calorific heat Bulb light light Motor mechanical motion Bell acoustic sound

On the way, they can interact with components that use up some of the energy for specific purpose.

Protection Components

The elements that interrupt the flow of the current when it gets too high are the PROTECTION COMPONENTS.

As a result, they protect the elements from damage. They can be fuses or circuit breakers, which are in the main distribution box every house.

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Circuit Symbols

Electric cell (DC) + BATTERIA + Electric resistors Battery (DC) C + F - Wire or cable Bulb Wires not connected Wires connected Bell Switch - O 3-way switch 0 Motor M Push button (push-to-make) PUSH Push button (push-to-break) Ammeter (current) A Fuse Voltmeter (voltage) V @ Rocío Yuste Mieres

Electric Circuits Examples

X + + 8 + + +

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Electric Quantities

Charge

The CHARGE is the amount of electricity stored in an object.

It is equivalent to the volume of water in the upper container in a water circuit.

It is represented by the letter Q.

It is measured in coulombs (C).

How many electrons are in a Coulomb? 1 Coulomb =~ 6.242.000.000.000.000.000 electrons! (6.242*10^18)

Current

The CURRENT is the number of electrons that pass through a specific point in one second.

It is equivalent to the water flow in a water circuit.

It is represented by the letter I.

It is measured in amperes or amps (A) and in milliamps (mA) 1A=1C/s

A current of one ampere is one coulomb of charge going past a given point per second.

So, in an example where 346 Amps are flowing in one cable, how many electrons are flowing?

346 A = 346 C/s 346 * 6.242*10^18 =2.16*10^21 or 2,162,500,000,000,000,000,000 Electrons per second.

Now, do you see why we use the unit of Amps? To be able to quantify the flow of electrons in a circuit.

We use an AMMETER to measure the current. You connect the ammeter in series to a receptor or receptors where you want to measure the current.

Ammeter has a very low resistance. Therefore, the current through the circuit is unaltered.

A A

Voltage

The VOLTAGE is the difference between the electrical energy at two points in a circuit.

It is equivalent to the height in a water circuit.

It is represented by the letter V.

It is measured in volts (V) and in millivolts (mV)

Voltage is what pushes electrons around a circuit. Without voltage the free electrons will move around between atoms, but they move around randomly so they aren't much use to us. It's only when we apply voltage to a circuit that the free electrons will all move in the same direction, causing current.

Voltage can exist without current.

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