Explain it please (electricity)

barneysplash

Hello all

Can someone please explain electricty to me?

I mean what is it?

What is voltage, amps curent and all that stuff?

I've looked at educational websites, like how stuff works etc. but I still can't get my head around it :mad:

I know it is like gravity in that it just happens but after that I'm lost!!!

Any help in laymans terms would be greatly appreciated.

Son Goku

barneysplash wrote: »

Hello all

Can someone please explain electricty to me?

I mean what is it?

What is voltage, amps curent and all that stuff?

Electricity is the flow of electrons. Amps is the amount of electrons which flow by a point every second in a current. An example is a battery with both its ends connected by a wire with electrons flowing from negative to positive. The amount of electrons passing through a given point on the wire every second basically gives you the ampage. The positive and negative ends of the battery will supply energy to the wire and the amount of that energy per electron is the voltage.

Pherekydes

You can use the 'water' analogy to get your head around it:

Higher water pressure = stronger flow

Higher voltage = bigger electric current

Small water pipe = smaller flow (resistance to flow)

Small gauge wire (or one that doesn't conduct well-higher resistance) = weaker flow of electric current

Big tank of water = large flow for short time or small flow for long time, until the tank is empty

Big battery = big current for short period (required to start a car) or small current for long period (car radio)

Voltage = force
i.e bigger voltage (force) = bigger flow

Amperes (or amps) = measure of current flow

Ohms = measure of resistance

Ohm's Law = in an electrical circuit, the current passing through a conductor between two points is directly proportional to the voltage and inversely proportional to the resistance between them.

I = V/R

I is the symbol for Electric current, V for voltage (also referred to potential difference or electro-motive force emf), R for resistance.

tak

Come on, Barney.

ZorbaTehZ

That analogy of a water tank never helped me tbh, infact it probably made things worse. As long as you can your head around the idea of electron flow then you shouldn't be too bad. SonGoku explains it well above.

Michael Collins

ZorbaTehZ wrote: »

That analogy of a water tank never helped me tbh, infact it probably made things worse. As long as you can your head around the idea of electron flow then you shouldn't be too bad. SonGoku explains it well above.

"Electricity" is an awful term really as it doesn't really mean anything. Of course it need not be electrons but anything that carries a charge. Current is often carried by protons or ions...

dudara

barneysplash wrote: »

I know it is like gravity in that it just happens

Electricity will not flow unless there is a source of electric potential ( ie a battery or power supply of some form) and a closed circuit is present.

Electricity is the flow of electrons. The faster you can get the electrons to move, the more current will flow. This can be achieved by increasing the potential difference (ie voltage) or by dropping the resistance of the circuit.

Electricity isn't easy to understand. Feel free to ask more questions.

barneysplash

Thanks for the posts.

Ok, I understand it a bit better now, am I right on these points?

A flow of electrons is a current. This is measured in amps

You needa difference in potential to make them flow. This is a voltage.
This is measured in volts.





But how do the electrons get pushed to start the flow? And if everything is made up of atoms, and you remove electrons from the atoms to make the current, should the substance not break down?


And what is AC and DC - I know it stands for Alternating Current and Direct Current, and that household electricty is AC and small things like mp3 players or camera take DC batteries to work.

Answers lead to more questions!

Son Goku

barneysplash wrote: »

But how do the electrons get pushed to start the flow? And if everything is made up of atoms, and you remove electrons from the atoms to make the current, should the substance not break down?

Possibly the deepest question, I'll leave the rest of the questions to others.

Physical objects naturally seek the lowest state of energy, so when they find themselves in a potential difference the will head for where the potential is the lowest.

JoeB-

I'm not an expert at all but I remember we did something about this in physics in school... The question was about how fast the electrons themselves travel when a current is passing through a wire...

In other words the electric field (as opposed to electrons themselves) may propagate at the speed of light, so flip a light switch now and a light 300,000 Km away will light up in one second, but clearly no individual electron actually travelled at that speed because that can't happen...

So anyway there was a technique to determine how quickly the individual electrons would travel... we were very surprised at the answer because apparently the electrons only travel one meter in about 14 minutes... This is going on memory from over 10 years ago so I could easily be wrong with the figures... it would also depend on the thickness of the wire... Anyway can someone remind me about how that calculation could be carried out?

Cheers
Joe

Michael Collins

JoeBallantine wrote: »

Anyway can someone remind me about how that calculation could be carried out?

Electrons themselves generally travel at a reaonably quick pace, the only thing is they dont travel in a straight line from one side of the wire to the other, they travel almost randomly in a 3D type motion. Imagining a swarm of bees, i suppose, would be a decent analogy. When a voltage is applied the swarm as a whole tends to "drift" in a prefered direction (towards the negative terminal). This is known as the electron drift velocity. As for the calculation of this drift velocity, it goes like so:

Suppose we have n electrons per unit volume in this wire, each travelling an average velocty v, in a wire of cross sectional area A and elementary electron charge q.

I = Current = Charge / Time = Q/t = nqAvt/t = nqAv

So v = I/nqA

Taking a particular example of I = 1.6 A, n=10^28, q=1.6 * 10^-16, A=1 mm^2, we get

v = 1 mm/s

At this speed it takes 17 minutes to travel 1 metre!

Son Goku wrote: »

Possibly the deepest question, I'll leave the rest of the questions to others.

Physical objects naturally seek the lowest state of energy, so when they find themselves in a potential difference the will head for where the potential is the lowest.

Or another, perhaps less theoretical way of looking at it, is the voltage you apply across something, creates an electric field across it and electrons in an electric field experience a force...

barneysplash wrote: »

Thanks for the posts.

A flow of electrons is a current. This is measured in amps

Well kind of, a flow of charge is a current and electrons carry charge. And charge per second is also known as amps...

You needa difference in potential to make them flow. This is a voltage.
This is measured in volts.

Yes a potential difference will cause them to move...but so will a magnetic field...so you don't *need* it per se.

But how do the electrons get pushed to start the flow? And if everything is made up of atoms, and you remove electrons from the atoms to make the current, should the substance not break down?

See Son Goku's reply or my response to him above...

And what is AC and DC - I know it stands for Alternating Current and Direct Current, and that household electricty is AC and small things like mp3 players or camera take DC batteries to work.

Answers lead to more questions!

Yep AC literally means alternating current and DC means direct current, although this is abused quite a bit in the area. You often see DC voltage or AC current etc, neither of which makes any sense really i.e. think about the meaning of "Direct Current Voltage" or "Alternating Current Current"!

All it means really is: for DC the quanitiy in question - be it voltage or current - stays constant with time, for AC it means it's changing - in particular AC means it alternates between positive and negative in a sinusoidal fashion - just look at a graph of the sinewave & you should see what it means.

Also see Wikipedia on:

Alternating Current and on
Direct Current

for a more complete description...

barneysplash

I appreciate the detailed responses, but I'm getting confused

So I'll try another simple way to ask for help. I'm sure some of you
remember doing things like this when you were small...


Say I have a AA battery, the kind you find in remote controls, mp3 players etc.

I also have some 2 bits of metal wire and a small torch bulb.

I connect 1 bit of wire to each of the battery's terminals.

Then connect the other end of the bits of wire to the bulb.

The bulb goes on.

What's happening?

Son Goku

When you complete the connection the positive charges exert a pull on the electrons and they move along the wire. When the electrons pass through the bulb they pass through a piece of tungsten wire in the bulb. The electrons strike the atoms causing them to heat up*. As you know things glow when they are very hot, so the wire at the centre of the bulb begins to glow. So now you have light!

barneysplash

Son Goku wrote: »

When you complete the connection the positive charges exert a pull on the electrons and they move along the wire. When the electrons pass through the bulb they pass through a piece of tungsten wire in the bulb. The electrons strike the atoms causing them to heat up*. As you know things glow when they are very hot, so the wire at the centre of the bulb begins to glow. So now you have light!

Is the positive charges exerting a pull on the electrons the voltage?

Where do the electrons come from? I assume it has something to do with the chemicals in the battery and that when the battery is "flat" there has been some chemical change that has exhausted the supply of electrons?

dudara

barneysplash wrote: »

Where do the electrons come from? I assume it has something to do with the chemicals in the battery and that when the battery is "flat" there has been some chemical change that has exhausted the supply of electrons?

You don't add or remove electrons (conservation laws), what you are doing is making them 'move' through the circuit.

A battery acts as a potential source because it is a clever combination of chemicals that provides a chemical potential. When a battery is flat, this means that the chemical potential originally contained in the battery has been depleted. This can be done by using the battery or by simply leaving it sit for a long period of time. (chemical potential cannot be stored indefinitely).

Pherekydes

In some batteries, the chemical reaction can be reversed, recharging the battery. In some batteries the chemical reaction cannot be reversed, i.e. they cannot be recharged.

In rechargeable batteries, you reverse the chemical reaction and recharge the battery by reversing the current flow through it. A car battery is an example.

kevmy

barneysplash wrote: »

Is the positive charges exerting a pull on the electrons the voltage?

Where do the electrons come from? I assume it has something to do with the chemicals in the battery and that when the battery is "flat" there has been some chemical change that has exhausted the supply of electrons?

You don't exhaust the electrons just the potential evens out. ie. there is the same number of negative charges (electrons) as there is positive charges so there is now no more potential.

The positive charges do exert "a pull" on the electrons. Opposites attract. It's just like magnets. The positive side is attracted to the negative side and vice versa. The positive side repels the positive side and the negative repels the negative.
So the electrons are drawn to the positive charges.

A Primal Nut

barneysplash wrote: »

Is the positive charges exerting a pull on the electrons the voltage?

Where do the electrons come from? I assume it has something to do with the chemicals in the battery and that when the battery is "flat" there has been some chemical change that has exhausted the supply of electrons?

The electrons are always there. Certain metals, however will also seek out more electrons to fill their outer shell, ie they are very reactive. As the basic rule of magnetism states, negative attracts positive and verse versa. It's the electrons (negative) that move towards the stationary positive side, as they are small and require little energy to move compared to protons. In order for the electrons to flow repeatedly they need energy. The law of conservation of energy states energy cannot be created or destroyed, but only changed from one form to another. The easiest way is to convert mechanical energy to electrical energy.

So basically, to generate electricity, a magnet spins around a piece of copper with a coil wrapped around it.
When the positive side of the magnet is close to the copper coil, the electrons flow in the coil towards the positive side of the magnet. As the magnet and coil are held apart, they never reach the magnet so they just lie there. When the negative side of the magnet is close to the copper coil, the electrons flow in the coil away from the negative side of the magnet. Now, if the magnet is attached to a turbine (driven by steam, wind, water, whatever) the magnet will keep spinning. The electrons in the coil "follow" the magnet around.

The voltage reaches its too peaks (positive and negative) when the positive and negative sides of the magnet are closest to the copper coil. So you can imagine the AC Sine Wave being generated as the magnet turns and that's how mechanical energy is converted to electrical energy. In the case of a wind turbine, for example the wind comes out of the turbine slower than when it went in because some of it has been converted to electrical energy (and heat as well). Then the electricity is brought from the coils down through wires. This might enter your house and if it goes to a bulb creates light and heat.

So the energy conversion chain could be wind>> mechanical >>electrical>>heat/light. Along the way there will be considerable losses in the conversion process, to resistance and excess heat energy. The electrical energy is voltage which pushes the electrons along as current. The amount is given by V=IR.

DC can be generated by placing a commutator which changes the poles of the magnet at just the right point so one pole (negative or positive) is always closest to the coil; therefore the electricity only travels one way.

Electricity also comes from batteries which I thought was explained well in the HowStuffWorks article on How Batteries Work.