## Thursday, 18 December 2008

### Potential

I'm trying to understand what is really meant by the words 'voltage' and 'current'. Voltage measures the energy per charge. Current is the 'flow' of electric charge, while voltage is considered to be the 'push' behind it. The push is created by something known as the difference in electrical potential. The difference in electrical potential between two points is known as voltage. So, what is meant by potential energy?

There was once a science experiment we tried at school. It involved pushing a little wooden car along a table, and then letting it fall over the edge to the floor below. Where's the science you might well ask? Well, attached to the back of the car was the end of a long flowing reel of ticker-tape. As the car moved along, the tape behind it passed through a machine which, once every second, punched an ink stained dot onto the tape. So if the car was stationary, all that would appear on the tape was one ink dot, and for each second that passed, another was over-imposed upon it. Once the car started moving, the tape would be pulled through the machine, and a line of dots would then start to appear. The faster the car was moving, the further apart the dots would be.

When the car sits idle on top of the table, it has a potential energy. The car's doing nothing but it has the potential to do something. If I push the car over the edge, it will fall, and crash to the floor. Okay, let's look at the ticker-tape. Where the car was doing nothing, the tape shows a rich ink stain where it has been repeatedly stamped. Then, little gaps start to appear between the dots because the car has left the table. These gaps grow further, and further apart as the falling car gains velocity. Wham.... the car's hit the floor and it's motionless. Now there are no longer any distances between the dots - there is just one dot which is over-imposed by another dot, for each second that passes. The car has returned to its previous state of doing nothing, but it still has the 'potential' to do something.

The difference in potential is between the car doing nothing (potential energy) - and doing something (kinetic energy). As the car falls it gains more velocity, its kinetic energy increases as its potential energy decreases. In theory, with a high enough fall, and no wind resistance, the car could keep falling and it would keep on transferring potential energy into kinetic energy.

Let's look at the ticker-tape again. Where the dots move further and further apart from one another, the potential energy could be described as being unravelled. The dots are also becoming less and less frequent, so we could say the energy now has a lower frequency. The energy is stretched by lower frequencies until ..... the car hits the floor. The car has now returned to a state of potential energy. So even though we think of the car as doing nothing, it's actually seething with energy. The energy was stretched to a lower frequency by its velocity, and then, when the car is motionless, it is squashed back together again.

In an electrical circuit the velocity of the charge flow is measured by current. Voltage would be a measure of the energy needed to push the car off the table. Supposedly, increasing the height of the drop also increases voltage, but this is based on the assumption that the force of gravity acts upon a falling object. Unfortunately, there's no such thing as time-space in my Universe, so there's no such thing as gravity. I will return to voltage in another post.

If you were on a hill and a huge boulder came bounding towards you, it's unlikely that you would raise a hand to try and stop it - because you know it would bloody hurt. When the boulder is motionless at the bottom of the hill, then that would be the more perfect time to approach it. It illustrates just how powerful energy is once it's in motion. A falling boulder is unravelling its potential energy, and transferring it into kinetic energy. Just a moment before the boulder reaches the bottom of the hill, will be the point where it will have reached its maximum velocity. This velocity determines the current. Perhaps voltage determines the size of the boulder.

There are two kinds of charge - positive and negative. So far the models with the car, and the boulder are describing how a positive charge works (in conventional electricity). Basically, a negative charge would work in the opposite way. If the boulder were a negative charge, it would roll back up the hill - and gain momentum. I'm going to explore this further in my next post. I'm also interested in how these models apply to the energy we recieve from the Sun.

Many thanks:
http://en.wikibooks.org/wiki/Electronics/Voltage,_Current,_and_Power
http://www.electricitycentral.com/articles/whatisvoltage.ht