Electrical Current
What is electric current?
Consider the circuit in Figure 1, where an electric field and an open switch are connected by a conducting wire. When the switch gets closed, the electrons from the negative plate or terminal will be attracted towards the positive terminal along the wire. This will happen quickly, and soon the charges will spread equally.
Assume that the electric field between the terminal is maintained, as in Figure 2. A battery is a source of electric field. Then, the electrons will flow as long as the electric field is maintained. Note that electrons do not get accumulated at the positive terminal of the battery, rather there exist a continuous flow of charges through the battery. We will discuss exactly how a battery works later. The point here is that electrons will flow.
The flow of electrons or the flow of charges is called the electric current.
The term current is used in the same manner used to describe water current in a river.
Mathematically,
average current = amount of charge flowed through a point / time taken
i=dq/dt
I=Q/T
What is a conducting wire?
Why is the flow of charges called electric current rather than charge current?
Why does the current flow?
Why is electric current significant to our study of electromagnetic energy?
I have used terms that were not discussed previously. Lets consider each questions in sequence.
What is a conducting wire?
A conducting wire also called a conductor is any material such as copper or aluminum, which can easily allow electrons to flow. Copper or aluminum have extra electrons in outer shells which allow for easy flow of electrons. Electrons flow by bumping onto each other. We will discuss about conductors, semi-conductors, and insulators in more detail at a later section.
Why is the flow of charges called electric current rather than charge current?
During 18th century, when an object is charged by rubbing or otherwise the "condition was called electric." Thus, the term electric is associated with charge. Thus, the charge current is commonly called electric current.
Why does a current flow?
The electrons flow because an electric field exists. There exist electric field between a region if there is a negatively charged plate and positively charged plate separated by some distance or the region. The electrons at the positive plate or terminal flow, because electrons are attracted to the positive plate.
Does electric current carry electromagnetic energy?
Electric current, or flow of charges is different from flow of electromagnetic energy. Current in the wires do not carry most of the energy, rather the electromagnetic energy is carried by electromagnetic waves travelling along or around current conducting wire carries much of the energy.
I have read in "Electronics the Easy Way" that millions of electrons travelling at about speed of light "produces great electricity". How truthful is that statement?
I am not certain whether the speed the book refers to is the spinning speed or the speed at which electrons travel inside the wire. The speed at which electron travel inside the wire is noted to be very small, thus electromagnetic energy can not be due their kinetic energy.
What is the relation between electric current and electromagnetic energy?
Here I quote William Betty, and I will return to the question in a different section. "We could almost say that electric current IS the
How fast does the current flow?
The rate of current flow depends on the strength of the electric field. The strength is measured in terms of voltage.
What is voltage?
There exist an attraction between a positive charge and a negative charge. Both have a tendency to be attracted to each other. When a positive charge and a negative charge is separated as shown in the Figure 3, the tendency of attraction is measured by voltage.
Voltage is a measure of the strength of the electric field. Voltage is "always measured between two charged objects". (I am using this definition, until I come a cross a more descriptive definition.)
What is the amount of current that comes out the three prongs?
The voltage at the three prongs is an alternating voltage of 120 volts. The current depends on the load or the device, which draws the voltage. The relation is characterized by the Ohm's law, which we will discuss later.
What is the alternating voltage? The electrons are moving up and down in a sinusoidal wave from.
What causes the electrons to move up and down?
What kind of electric field is required to cause such a pattern?
What is an alternating voltage source?
Before we can discuss about alternating voltage or current, we have to investigate magnetism and the relationship between magnetic force, field and electric current.
I've come across magnets, but what really are magnets?
(Continuity Question)