Electrical current
Subject classification: this is a science resource. |
Educational level: this is a secondary education resource. |
Type classification: this is a lesson resource. |
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Welcome to this lesson on Electrical Current.
Purpose[edit]
In this lesson the flow of electrons, electrical current, is described and characterized in contexts of voltage, resistance, and simple, useful electric components.
Definition of Electrical current[edit]
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. Electric current is denoted as I measured in unit Ampere A
Electrical current(or current)is movement of electrons in a conductor.Since electrons need not be bound to atoms, it is important to exclude atoms, conductors, resistors, what have you in our definition of current flow.
A voltage or electromagnetic force causes movement of electrons in a conductor.
- Ohm's law
Hence,
Electrical current(or current)is movement of electrons in a conductor.Since electrons need not be bound to atoms, it is important to exclude atoms, conductors, resistors, what have you in our definition of current flow.
Hence,
- .
Electron flow excitement[edit]
So, when electrons flow through a material, they cause anything from an insignificant quantity to a catastrophic amount of vibrational energy or heat to be created.
Current carriers[edit]
Insulators do not normally allow electron flow.
To overcome that effect, voltage would have to be raised tremendously high. For a spark to cross the insulating gap of air between his finger and the office door, the cube farmer would have to build up thousands of volts of static potential. However, there is only the air there to be heated and so it simply has too few bits of matter to support heating. Vacuum, as you already surmised, has only the electrons themselves and only during the course of their passage.
Semiconductors will begin conducting after only a little voltage 'encourages' the flow.
Before, it acts like an insulator. After, it acts like a conductor. Resistors are designed to resist the flow of electrons. They may be of many materials and, in fact, even conductors display the same characteristics, but to a far smaller extent. Resistors are manufactured as identified components in circuitry. Not surprisingly, the filaments in electric lights, electric stove coils, blow dryer elements and space heater coils are also resistors.
Conductors allow electrons to flow quite freely.
They do, however, present some resistance to current flow. Thus, you can cause them to heat up by 1) passing more than the designed current or 2) insulating them so that the tiny heat that is normally generated has nowhere to go and builds up to a potentially disastrous temperature.
Superconductors are conductors with the characteristic of passing electrons with negligible heating and resistance.
The current state of technology insists that they be cooled to a very low temperature. Should room temperature superconductors ever be created, there would be no power wasted over the (currently resistive) power lines between our power plants, and our cities and towns. That would cut carbon emissions, well, a whole lot.
Hot and hotter[edit]
In a lightbulb, that heat becomes so great that the tungsten filament glows white hot. Stove and blow dryer elements can glow red-hot. A space heater may not glow but it can still burn the dickens out of you if you are not careful. Light generated is directly related to temperature. If two objects give off the same color of light, they share identical temperatures.
The amount of heat energy disspated into the surrounding is considered heat energy loss can be calculated as
- For Conductor
- For Semi conductor
Experimentation in current carriers[edit]
Experimentation is used to determine a substance's resistance characteristics with regard to current flow. Experimental results show that increasing the conductor size decreases its resistance proportionately. So, double the cross-section of a wire and you halve its resistance.
The unit of current is the Ampere or Amp for short. It is defined as a specific number of electrons flowing across a specific point per unit time.
Current, Power and mathematic equations[edit]
We have spent a great deal of time talking about current and its thermal effects. Let's consider what we know. When voltage goes up in a circuit, current goes up. If I double the voltage and the resistance remains constant, I double the current. I also double the vibrations I'm causing so I double the amount of heat I am adding.
In other words, doubling voltage doubles the power generated in the form of heat. This leads us to an equation. Power equals Current times Voltage. The symbol for Power is P, the symbol for Current is I, and the symbol for voltage is E. We have
As I double the resistance, I halve the current when constant voltage is applied. Resistance and current are inversely related. As I double the voltage, the current doubles as well. In point of fact, Voltage equals Current times Resistance or E = I * R.
Look up the definition of an Amp. Calculate the value of 50 amps in the terms you found. Provide at least three correct answers. For extra credit, write a paper on Tesla (the inventor, not the band). If you plagiarize Wiki, you will be found out.