Bit of a strange question, but what is it? My physics teacher said it was kind of like a "push" that pushes electrons around the circuit. Can I have a more complex explanation? Any help is much appreciated.
Electronic – What exactly is voltage
voltage
Related Solutions
You have that backwards. Electrons move through an electric field so that they lose their potential: i.e. from a place of higher potential to a place of lower potential.
There are several useful examples to consider.
Suppose that the power source for the circuit is an object containing separated charges, such as a capacitor with it two plates that have opposite and equal charges. Electrons will flow from the (-) plate where there is a surplus of them through our circuit elements to the (+) plate where there is a dearth. As this happens, the voltage on the capacitor slowly goes down, until the plates no longer separate charges: the voltage is zero.
Why do we still call this a circuit when the electrons simply move from one place to another? Although no individual electron actually crosses the capacitor, it does look as if electricity is flowing across the capacitor simply because electrons are entering one side and at the same time leaving the other, and they are all identical: we cannot label our favorite electron and see whether it goes in one side and out the other. So the capacitor, and its load, do appear to form a complete circuit even though the capacitor is actually internally open.
Using a capacitor as a source of electricity is similar to water powered machine. We pour water into an upper reservoir, and it flows down from there, powering our machine via a turbine, and collects in some lower reservoir. In its descent, the water loses gravitational potential energy. When the upper reservoir is empty, the machine stops working. Someone has to come in and recharge the machine by doing work: transferring the water back to the upper reservoir, lifting it against gravity. (The gravitational analogy is not perfect, because there are no negative and positive masses, like there are negative and positive charges. The similarity is that it takes work to separate two masses to overcome gravity, and it takes work to separate opposite charges to overcome the attractive force caused by the field.)
Now, unlike a capacitor, a battery contains a chemical reaction which continuously produces a fresh separation of charges. (Incidentally, the word "battery" once referred to an array of capacitors, not to chemical cells!) With chemical cells, we no longer worry about running out of the small capacity of electrons stored in a plate, because a chemical reaction is replenishing them. Of course, the reaction will eventually reach equilibrium and stop. But that can take much longer. For example, alkaline batteries hold a lot more energy than capacitors. In a battery circuit, the same electron will go around multiple times: it is a true circular path. The spent electrons go back into the battery, where the chemical reaction carries them against the electric field back to the negative electrode, restoring their potential energy. The energy of the chemical reaction performs work on the electrons, transferring its energy to them.
We can also pump electricity continuously, using generators. By moving a coil in a magnetic field, we can keep inducing a voltage, forcing the electrons to keep going around and around in the circuit. This is like adding a pump to the water machine, so that someone can just turn a crank to pump the water back to the upper reservoir, allowing the water-powered machine to run continuously. A changing magnetic field forces the electrons to move inside the coil, so that a voltage develops and then the electrons flow through the rest of the circuit back into the other side of the coil. By fluctuating the magnetic field, we create a back and forth motion of electricity through the circuit (alternating current, AC). That by itself can be used as a source of power for many kinds of devices, and can be rectified to direct current (DC) for devices which require it.
Think as power supplys as a constant voltage, rather than the current they can provide. So a constant voltage supply will try to maintain the same voltage independent of the load you put on it (until, as you said, it blows up). So, a fan is designed to "pull" or "let pass" 1A for a given voltage while an air conditioning device is designed to "pull" 10A for the same given voltage. Thats why they pull different currents. And, while you can "force" more current with more voltage, some devices are smart enough that they will try to compensate for that using their regulators (switching or linear) by having their own constant voltage supplies on the inside, thus maintining about the same current consumption up to a given voltage. Normaly supplys fail not because they fail to push the current, but because they fail to provide the current that is being "pulled". If you have a constant current supply, when you try to "push" more current to a given resistive load, the voltage will rise.
About the phone, battery charging ICs will often have a limit to the current they can charge (as will the batteries). Often on cellphones that limit is close to 1A. Hence you can charge it faster on 1500mA. The 200mA rating is probably based on the USB standard max current, and is obviously easier for the manufacturer to supply you with the phone because its cheaper than a 1500mA supply.
p.s.: to better understand different current draws for same voltages: http://en.wikipedia.org/wiki/Ohm%27s_law also remember that not all loads are resistive(most arent)
Best Answer
Your teacher was right.
Current is electric charges (usually electrons) moving. They don't do that by themselves for no reason, no more so than a shopping cart moves across the floor of a store by itself. In physics, we call the force that pushes charges the electromotive force, or "EMF". It is almost always expressed in units of volts, so we usually take little shortcut and say "voltage" most of the time. Technically EMF is the physical quantity and volts is one unit it can be quantified in.
EMF can be generated several ways:
This effect can be scaled up to make vary high voltages and is the basis for how Van de Graaff generators work.
The total voltage you get from one out and back, even with a high temperature difference is pretty small. By putting many of these out and back combinations together, you can get a useful voltage. A single out and back is called a thermocouple, and can be used to sense temperature. Many together is a thermocouple generator. Yes, those actually exist. There have been spacecraft powered on this principle with the heat source coming from the decay of a radio-isotope.
Electron tubes use this principle in part. Instead of heating something so that electrons fly off on their own, you can heat it to almost that point so that they fly off when a little extra voltage is applied. This is the basis of the vacuum tube diode and important to most vacuum tubes. This is why these tubes had heaters and you could see them glow. It takes glowing temperatures to get to where the thermionic effect is significant.
This principle is also used in many barbecue grill igniters. A spring mechanism whacks a quartz crystal pretty hard so that it makes enough of a voltage to cause a spark.