The last time I was asked this, I found someone who could answer it a lot better than me. Here you go...
Understanding Light Energy
Thursday, June 26, 2008
Voltage, Current, Electrical Energy
Understanding Current
Firstly, current is simply the flow of charge. Some people think of this as electrons flowing continuously through the circuit, like a constant stream of cars driving from your home to school, back, on again, back again — in a loop. That is not strictly right. Instead, what happens is that an electron moves from one atom to the next, transferring a charge. Next the same electron OR another electron, moves on further, to the next atom. So regardless of how far each electron travels, the charge continues to travel.
One way to think of this is for a line of people to start with a bag of identical marbles. If the previous person passes you a marble, you mix it in your bag, then pass one marble to the next person, all that matters is that one marble has passed through your hands, regardless of whether it was the same marble or not. Get it?
So having made this important distinction, let me still use the (quite wrong) analogy of the stream of cars to explain the difference between a series and parallel circuit.
Series & Parallel
If there is only one route from your home to your school, if the traffic stops flowing on one of the road segments, it stops flowing on the entire route. That is what happens in a series circuit. If the circuit is broken, there is no way for the charge to get through, because that is the only route.
Now consider a parallel circuit, which means that there are at least two independent routes from your home to school. If traffic is flowing in both circuits, then a break in one will not stop the charge flowing in the other circuit. To put it simply, you can always take the other route.
Potential & Kinetic.
Remember the difference between potential and kinetic energy? Potential energy can do no work, so in one sense it is useless. However, it has the potential to be converted into other forms of energy, which can do work! The most common examples of mechanical potential energy are to do with gravity. This is gravitational potential. If you stretch a spring, that is elastic potential. Release it, and the potential energy turns into kinetic energy, which can do work. Similarly, a chemical compound may have potential energy locked up in it which may be liberated as, say heat. That is chemical potential.
There are several other kinds of potential — nuclear, thermal, electrostatic... But let us stay with gravitational potential, the simplest to understand.
When you toss up a basketball, you are increasing its gravitational potential. The height you toss it to decides how much you increase the potential. The ball falls because there is a difference in potential between its highest point and the lower point AND it is allowed to travel betwen them. The potential difference is what pushes the basketball down. On a flat surface, all points would have the same gravitational potential, and the ball would not move at all. However, if you placed the ball in a tree, it would have potential difference, but no clear path to fall. It has the potential, but is not allowed to transform into kinetic energy.
Electrical Potential, alias Voltage
Now think about Electrical Potential. If the potential everywhere on the circuit was the same, no charge would flow. However, when you build up potential on one side, then if you provide a path, charge will flow to the other side. One way to do this is to insert a battery into the circuit. Think of it as a pump for electrical charge. It is ready to push, but if you don't connect a pipe, it has nowhere to send the charge. We connect the pipe, and the charge flows.
This potential difference is what we call Voltage. The actual flow of charge is what we call Current, – a measure of the rate at which charge flows in a circuit. So you can think of voltage as the size of the push that the electrons are receiving. If the circuit is open, no current can flow. If the circuit is closed (connected), then current will flow. So you can have voltage without current, but never current without voltage.
Positive or Negative?
Which is positive and which is negative is simply a matter of convention. As we have seen, the charge that flows in a circuit is not identical to the way the electrons flow. Now the charge may consist of electrons, which are negative, or ions, which may be positive or negative. The convention is ALWAYS that current flows from the positive to the negative. This if fine when positive ions (cations) are flowing. Then the particles are moving in the same direction as the current. However, when it is electrons or negative ions (anions) that are flowing, then the particles actually flow in the opposite direction to the direction of the current according to convention. In a closed circuit, it is practically unimportant what the actual direction is, so we can comfortably accept the convention that electrical current always flows from the positive to the negative.
Firstly, current is simply the flow of charge. Some people think of this as electrons flowing continuously through the circuit, like a constant stream of cars driving from your home to school, back, on again, back again — in a loop. That is not strictly right. Instead, what happens is that an electron moves from one atom to the next, transferring a charge. Next the same electron OR another electron, moves on further, to the next atom. So regardless of how far each electron travels, the charge continues to travel.
One way to think of this is for a line of people to start with a bag of identical marbles. If the previous person passes you a marble, you mix it in your bag, then pass one marble to the next person, all that matters is that one marble has passed through your hands, regardless of whether it was the same marble or not. Get it?
So having made this important distinction, let me still use the (quite wrong) analogy of the stream of cars to explain the difference between a series and parallel circuit.
Series & Parallel
If there is only one route from your home to your school, if the traffic stops flowing on one of the road segments, it stops flowing on the entire route. That is what happens in a series circuit. If the circuit is broken, there is no way for the charge to get through, because that is the only route.
Now consider a parallel circuit, which means that there are at least two independent routes from your home to school. If traffic is flowing in both circuits, then a break in one will not stop the charge flowing in the other circuit. To put it simply, you can always take the other route.
Potential & Kinetic.
Remember the difference between potential and kinetic energy? Potential energy can do no work, so in one sense it is useless. However, it has the potential to be converted into other forms of energy, which can do work! The most common examples of mechanical potential energy are to do with gravity. This is gravitational potential. If you stretch a spring, that is elastic potential. Release it, and the potential energy turns into kinetic energy, which can do work. Similarly, a chemical compound may have potential energy locked up in it which may be liberated as, say heat. That is chemical potential.
There are several other kinds of potential — nuclear, thermal, electrostatic... But let us stay with gravitational potential, the simplest to understand.
When you toss up a basketball, you are increasing its gravitational potential. The height you toss it to decides how much you increase the potential. The ball falls because there is a difference in potential between its highest point and the lower point AND it is allowed to travel betwen them. The potential difference is what pushes the basketball down. On a flat surface, all points would have the same gravitational potential, and the ball would not move at all. However, if you placed the ball in a tree, it would have potential difference, but no clear path to fall. It has the potential, but is not allowed to transform into kinetic energy.
Electrical Potential, alias Voltage
Now think about Electrical Potential. If the potential everywhere on the circuit was the same, no charge would flow. However, when you build up potential on one side, then if you provide a path, charge will flow to the other side. One way to do this is to insert a battery into the circuit. Think of it as a pump for electrical charge. It is ready to push, but if you don't connect a pipe, it has nowhere to send the charge. We connect the pipe, and the charge flows.
This potential difference is what we call Voltage. The actual flow of charge is what we call Current, – a measure of the rate at which charge flows in a circuit. So you can think of voltage as the size of the push that the electrons are receiving. If the circuit is open, no current can flow. If the circuit is closed (connected), then current will flow. So you can have voltage without current, but never current without voltage.
Positive or Negative?
Which is positive and which is negative is simply a matter of convention. As we have seen, the charge that flows in a circuit is not identical to the way the electrons flow. Now the charge may consist of electrons, which are negative, or ions, which may be positive or negative. The convention is ALWAYS that current flows from the positive to the negative. This if fine when positive ions (cations) are flowing. Then the particles are moving in the same direction as the current. However, when it is electrons or negative ions (anions) that are flowing, then the particles actually flow in the opposite direction to the direction of the current according to convention. In a closed circuit, it is practically unimportant what the actual direction is, so we can comfortably accept the convention that electrical current always flows from the positive to the negative.
What to do with the CO2? Wash it out!
Is that possible? Can we actually scrub carbon dioxide from the air?
Well, there's a group of scientists that believes we can...
Here's the story: CO2 extractor
Which way should a windmill face?
So the wind blows from the south, and we build a windmill facing south. The wind shifts to the north. We can either build a second windmill, or build one which rotates to face the wind. Or we can do this...
As with many technology advances, this started with a simple solution – the idea of turning the windmill on its back! Not only does this make the wind direction irrelevant, but the windmill is pretty compact. Read about it here:
Credit: Mariah Power
Wednesday, June 25, 2008
Lighting innovation
Our exposure to new technology in lighting is usually limited to choosing between CFLs and new LED lights for our rooms. However, it is important to remember that large parts of India and Africa do not have reliable access to power.
Photo Credit: The World Bank, International Finance, Lighting Africa, CNetnews.com
The good news is that a lot of entrepreneurs are working on this problem. (In the hills, we have an LED lantern that is charged by a small solar panel. We go back after a year, and find that this wonderful little lamp is still holding a charge and lighting up the room! ) Even our lamp is primitive, when compared with newer technology.
Here's the story, with lots of pictures: Let there be light beyond the grid
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