Basic Electricity

Electricity is the energy that makes everything

from toasters to televisions work. It is

also linked to magnetism. Together, as electromagnetism,

they are one of the four fundamental forces

holding the Universe together.

Most electricity is generated in power stations by magnets that spin

between coils of wire to induce an electric current.

The magnets are turned by turbines, which are themselves either turned by steam heated by burning coal, oil or gas, or by nuclear fuel, or turned

by wind or water.

The stronger the magnet, the faster it turns, the more coils there are, so the

bigger the voltage created.

The four basic concepts we need to understand electricity as relates to

audio are as follows:

• Voltage

• Current

• Resistance

• Power

An electric charge that does not move is called

static electricity.

A charge may flow in a current

providing there is an unbroken loop,

or circuit.

A current only flows through a good conductor such as copper,

namely a material that transmits charge well.

A current only flows if there is a driving force to

push the charge. This force is called

an electromotive

force (emf).

The emf is created by a battery or a generator.

Currents were once thought to flow like water. In fact they move like a row of marbles knocking into each other.

In a good conductor there are lots of free electrons that are unattached to atoms. These are the ‘marbles.

This difference, called the potential difference, is measured in volts.

The rate at which current flows is measured in amps.

Voltage

Voltage is commonly referred to as electrical pressure.

An analogy that is often used is that voltage is like the pressure of water which is stored in a dam.

Electric potential difference, potential drop, electromotive

force, electric tension...

Voltage is the potential for current in the same way water pressure is the potential for flow.

Voltage is the force which causes current to flow through an electronic circuit. Two sources of voltage are batteries and general power outlets.

Current

All substances in the universe are made up of

atoms.

Atoms are made of

protons (+ve charge),

neutrons, (neutral

charge), and electrons (-ve

charge).

The electrons are the important thing here: they collect around the central

part of the atom and the number of

electrons around the atom will give an atom its overall

negative or positive charge.

That means that some substances

conduct electricity, which is simply

electrical charge, easily- substances like copper, gold,

silver. These substances are conductors.

There are two types of current flow:

Direct current and Alternating

current.

Direct current means current

flows in one direction, from

negative to positive.

Direct current is used to charge batteries, and in nearly all electronic systems, as the power supply. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. Direct current is used for some railway propulsion, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

Like the difference in height between the top of the dam and the bottom, there is an excess of electrons within the minus portion of the battery, which is expressed as voltage (AA battery is 1.5v for example)

Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams.

The electric charge flows in a constant direction, unlike alternating current (AC).

The detailed movement of

electrons in AC current gets very complex and depends on the exact conductor being used

but, simplistically, the electrons simply move

back and forth (away from and then towards the

generator) over a short space.

In a DC water hose, a molecule of water can only perform work e.g. moving a turbine, when it travels from one end of the hose to the other. However, in an AC water hose, a molecule of water just oscillates around its starting

location and it is just the force of the molecule hitting the next

molecule in the chain that transmits the energy.

The last molecule in the chain is always the one that strikes the turbine and performs the work.

Electric fields work in a similar way to gravity with an important exception being that while gravity always attracts, electric fields can either attract or repulse.

American Benjamin Franklin carried out extensive electricity research in the 18th

century, inventing the lightning rod amongst his

many discoveries. Lightning rods protect

buildings in the event of lightning by conducting lightning strikes through

a grounded wire.

So, “50 cycle hum" is the sound of AC

current leaking into the audio

chain somewhere

along the line.

Alternating current is the type available from a GPO.

Alternating current changes

polarity at regular

intervals. House current changes

direction 60 times per second.

Advantages of ACThe big advantage that alternating current provides

for the power grid is the fact that it is relatively

easy to change the voltage of the power, using a device called a transformer.

The image above shows a typical power distribution system. Because power plants must ultimately provide electrical power to potentially remote locations, they generate high voltages to transmit the current to these areas. Multiple power transformers must be incorporated into to the system in order to gradually step down the voltage for safe residential use. Transformers may be used:

to reduce voltage from 500 kV long distance transmission to 69 kV localized transmission

to reduce transmission voltage to 12 kV distribution voltage at a substation

to ultimately reduce distribution voltage to 110/220 V residential or commercial service

So power companies convert alternating current to very high voltages for transmission (such as 1 million volts), then drop it back down to lower voltages for distribution (such as 1,000 volts), and finally down to 120 volts inside the house for safety. As you might imagine, it's a lot harder to kill someone with 120 volts than with 1 million volts (and most electrical deaths are prevented altogether today using GFCI outlets).

50HzAustralian Power oscillates 50 times per

second.

This means it’s 50Hz. It’s voltage is 230.

Its frequency when it gets into the audio chain, sounds exactly like 50 Hz, because it is.

The US use 120V at 60Hz

Europe 220 volts at 50 cycles

(Everywhere in the world is either 50 or 60 cycles, but the Voltages change)`

Earth.Circuit ground versus earth

Voltage is a differential quantity. To measure the voltage of a single point, a reference point must be selected to measure against. This common reference point is called "ground" and considered to have zero voltage.

This signal ground may not be connected to a power ground. A system where the system ground is not connected to another circuit or to earth (though there may still be AC coupling) is often referred to as a floating ground.

Separating low signal ground from a noisy

groundIn television stations, recording studios, and other installations where sound quality is critical, a special signal ground known as a "technical ground" (or "technical earth", "special earth" and "audio earth") is often installed, to prevent ground loops. This is basically the same thing as an AC power ground, but no general appliance ground wires are allowed any connection to it, as they may carry electrical interference.

That is why only audio equipment is connected to the technical ground in a recording studio.

In most cases, the studio's metal equipment racks are all joined together with heavy copper cables (or flattened copper tubing) and similar connections are made to the technical ground. Great care is taken that no general chassis grounded appliances are placed on the racks, as a single AC ground connection to the technical ground will destroy its effectiveness.

For particularly demanding applications, the main technical ground may consist of a heavy copper pipe, if necessary fitted by drilling through several concrete floors, such that all technical grounds may be connected by the shortest possible path to a grounding rod in the basement.

Loads

Why do I have to know about power and electricity, when all I am doing is mixing music?

Because this can happen.

Uluru gala dinner 31/7/13

What is a load?The term "load" is used in different

contexts, and its meaning can change slightly depending on context.

In the most general sense, the load is the thing that is connected to the output of an electrical circuit. The load can basically be anything. For example, it can be a resistor, or a capacitor or an inductor, or a transistor, or a motor, or an air conditioner or an amplifier.

The term "load" can also mean "the amount of power" or "the amount of current" drawn by the thing that is connected to the output of the circuit.

For example, think about a battery. If we were to say that there is a heavy load connected to the battery, or that the battery is supplying a heavy load, we would mean that the thing (load) connected across the battery's terminals was drawing a lot of current (or power).

"Load" can also be used as a verb. We might say that the graphics card in a computer was "loading down" the power supply too much, and by that we would mean that the graphics card was drawing too much current (or power) from the power supply.

It would be correct to say that all loads draw current (or power) from whatever circuit they are connected to. It would not be correct to say that they draw voltage or otherwise "take" voltage from their supplying circuit.

Current vs Voltage

Voltage (electric potential) is required to move charge (electrons) through the load or circuit, but voltage doesn't actually "go" anywhere.

That is what can happen when you try to get cables to carry too heavy a load. The heat gets too much and that is how fires are caused.

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