h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

That's it, really.

Traveller in Time trying to keep it real simple
"The Voltage is urge with wich the electricity would like to flow.

The Amperes are the flow speed that it manages to get.

The Watts is the amount of energy involved, you wil find this on your energy bill.


The Voltage is the potential, the Amperes are the current and the Watts is the heat produced in the process. "

The Watt is actually a unit of power.

That is, it is energy applied per unit time.

It doesn't have to be anything to do with electricity - horsepower when related to car engines is also a unit of power.

You can think of voltage and current as cause and effect.

If you apply a voltage, over a given material of fixed resistance, a defined current (flow of electrons) will result. The voltage is the cause, the current is the effect. The wattage is the level of energy generated at any time from the resulting flow of current.

It's a bit like economics** - if you set the set a really good price, loads of people will buy your product. If you set a bad price, few people will. The "voltage" in this case is the price, the number of products shifted is the "current", and the money you make at any time, specifically the voltage multiplied by the current, is the power.

(I know, I know, there are some difficulties with this allegory, (specifically that, as you increase price, sales drop, whereas when you increase voltage, current increases, but it's the best I can come up with at the moment)

Right...
I'm trying to construct an analogy in my head that would help me to understand this.
So if you have, say, a car- what are the volts contributing the process of the car running? I hope that isn't a stupid question. It probably is.

Okay, just read woodpigeon's post. Now... Hmm...

No, I'm not sure I understand it at all. This could be a long day.

Looks like I muddied the waters

Ok - think of voltage in terms of the level of attractiveness that something has.

If it's enormously attractive, lots of electrons will be enticed, and therefore a "current" (movement of electrons) occurs.

Attractiveness could be price, sexuality, magnetism, gravity, and in the case of electricity, a large positive charge. The result is always the same - objects / items / people of a certain type (if they are allowed to) come running.

Have I just cranked the muddy stick even more?

Um... maybe?

Right. Okay, so... My oven needs lots of little people in it to make it work (yes, this is the level we're at. No comments please). This is the voltage? Obviously the exodus of little people from the plug socket in the wall requires a large current and the current is measured in amps. Am I close?

Is this how George Bush feels EVERY DAY?

Think of a tank of water with a hose leading to the ground.

The voltage is the height above the ground i.e the potential to cause flow or current. The higher the tank is above the ground, the higher the potential to cause the water to flow.

The current, amps, is a measure of the rate of flow of the water flowing down the pipe.

The diameter of the pipe is the inverse of the resistance i.e. the smaller the diameter the greater the resistance and the lower the flow or current.

Watts are the ammount of power caused by the water flowing. Imagine a paddle wheel placed in the pipe. More or faster water flow causes the wheel to turn faster.

In the old days, the analogy of water flowing in a pipe was usually used to explain volts and amps, but nowadays people don't really have an instinctive feel for water flow, so the following may not help.

Volts is the like pressure of water. It's what pushes the electricity around. Amps is the current; it is the same as the amount of water flowing in a pipe per second. Resistance is like a barrier with a hole in it, preventing the water from flowing in the pipe. The smaller the hole, the harder it is for the water to flow, so either the pressure has to be higher or the current will be lower.

There's no obvious analogy in water terms for Watts. Both water flow and electricity flow will involve energy, but it's not obvious.

Watts is the pressure (voltage) multiplied by the current.

I can give you plumbing analogues for alternating current, capacitance and inductance as well, if you are interested.

Traveller in Time listing the voltages to make a car move
"First you need the remote unlocking device --3V
This will activate the lockmotor in the doors --12V

You turn the key for the ignition --12V
The ignition makes sparks inside the engine --400V up to 700V

Most trucks and some vans use 24V batteries instead of the 12V petrol car type.

In case of an electical driven car chances are the drive engine is powered with 48V batteries.

All battery voltages are 'Direct Current' == DC the voltage does not change over (short) time. (lasting use will deplete batteries).

The only way to efficiently generate electricity in a car is using motion to drive a dynamo, this kind of device generates (internally) 15V AC. The AC is rectified and current limited to recharge the battery. "

Your oven is connected to an electrical cable where large numbers of electrons are whizzing - first forwards - and then backwards through the cable at the speed of light. This flow of electrons heats specially designed elements in the oven, and you get the heat you need to roast or bake something.

Now, think of there being a big power-station somewhere, connected by a metal cable to your oven. The cable starts at one side of the power station, runs into your house and through your oven, and then back to the other side of the power station. Connecting the cables in the power station is an electrical generator that is continuously switching voltages. First it makes one side of the cable positive and the other side negative, and then it switches the voltages to negative/positive.

Electrons flee from the negative voltage towards the positive voltage, running through your oven as they do so. Then, they reverse tracks and flow in the opposite direction through your oven. (This is what is known as "alternating current" or AC)

If the people in the power station increased the voltage, then *more* electrons would run through your oven. You would also notice that the oven would get hotter.

<<"first forwards - and then backwards through the cable at the speed of light.">>

Ouch, no.

Electrons have mass. They don't move at the speed of light.

Electrons in a cable don't move particularly fast at all, but the wave front of the current will be a significant fraction of C.

I wrote a big reply earlier using a rollercoaster to explain things but I accidentally deleted it and then couldn't be bothered retyping it.

However, things look confused here so here it is again.

For the best thrill one wants a really fast roller coaster. And how do they do that? They crank the train up as high as possible above the ground. This give the rollercoaster train higher 'potential energy'.
When the train is let go, the higher it is from the bottom then the more speed or 'kinetic energy' it can achieve.

So the height is the potential difference - which is analogous to potential difference in electricity.
Electricity is usually a flow of negatively charged particles called electrons. Because they are negative they are attracted to positive things. So to get them to move you make one end of your wire postive and the other end negative. This creates a 'potential difference' - the electrons are no longer happy where they are and so flow towards the postive charge and away from the negative charge.
This flow is the current and is measured in amperes (or amps A) - the more electrons and the faster they go then the higher the current.

TO make the current higer you make both the positive and negative ends of the wire more highly charged and the ne

Arse, I'm not having much luck with this post...


...TO make the current higer you make both the positive and negative ends of the wire more highly charged and so have a higher potential difference (same as making the top of the roller coaster higher and the bottom lower). The potential difference is measured in volts.


Volts and amps are related in the equation V = I x R

V is volts and I is the current (amps).

R is a property of the material the electrons flow through that tries to prevent the flow of electrons. It is called resistance and is measured in Ohms.

"The Watt is actually a unit of power."

Have you no respect for the laws of comedy?
That piece of info must always be phrased as "watts the unit of power" for maximum effect.

"You will find watts on you energy bill. "

I never got the potential energy thing. Surely anything that prevents the passage of energy from reaching its potential is affecting that same potential by reducing it. This has confused me since I were a lad and I doubt I'm going to understand it now.

Stretch an elastic band - you can literally feel the potential energy in the rubber.