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From chemistry we know that the atoms are the tiniest component of a matter that still possess the properties of a chemical element. Also, there are some discussions in chemistry about the chemical reactions between different elements. Those reactions are initiated by the exchange of electrons between the atoms of different elements. Now, electron is a subatomic particle, meaning that is part of an atom (even smaller than an atom), and there is chemical property for it. Basically what gives a matter its properties is the formation of its atoms and atoms can be different based on the structure of their subatomic particles. Further details goes into the subject of chemistry.
What we are dealing with here, is another property of the subatomic particles (such as electrons) which is called Electric Charge and the unit of this electric charge is Electrostatic Nnit (esu). The electric charge of an electron is negative 1 esu. The electric charge of the other two subatomic particles, namely proton, and neutron is positive 1 esu and 0 (no charge). The SI unit for electric charge is Coulombs (C) and one coulomb is about 6.24 x 1018 esu. It is good to know that the charge of an electron is 1/ (6.24 x 1018) = -1.6 x 10-19 C.These electric charges can only move from one place to another and won't die or vanish. This concept is one of the principal laws of physics called the conservation of charge. an Electric Field should exist in order for an electron to move to a new location (atom!), but what is an electric field? Whenever there is an electric charge, and electric field is generated around it and is shown by Newtons per Coulomb (N/C), or Volts per Meter (V/m). The electric field is usually shown by arrows called Electric Flux (Ψ). Total electric flux generated by a charge is equal to the charge (Ψ = Q)
How much an electric flux pass through a material depends on the material. For example, it can never pass through conductive metals. This property of the material on how much it lets the fluxes of an electric field to pass is called Permittivity which is shown by the ε in the Coulomb's Law equation. The electric field E created by a charge Q1 at distance r, is therefore calculated as
E = Q1/(4πεr2). The electric fields shown in the picture above are radial because the charges are Point Charges. If our charge is a line charge, then the fluxes are also straight lines connected to the line charge. The Line Charges are shown by their density (ρL) per unit of length like Coulmbs per meter (C/m). Then the flux density is shown by the number of fluxes per unit area perpendicular to the fluxes, which becomes Coulombs per meter square (C/m2). The electric field of a line charge is calculated as
E = ρL/(4πεr). This story goes on and we will have Sheet Charges with density (ρs) and their electric charge is calculated as E = ρs/(2ε). It can be observed that the electric charge from a point charge is inversely related to the square of its distance, for a line charge is is inversely related to the distance and for a sheet charge is not related to the distance at all. This relationship is because the line and sheet charges are assume to be infinite in size and the distance is too small compared to their size.
These arrows show the direction of the force applied by the electric charge. for example the protons introduce a positive charge into the field which is outward of the proton. Try to put two positive sides of a magnet close to each other. They both insert the same force and that separates them from each other, and vice versa. If we have a charge Q, inside an electric field E, the force FF that is applied to that charge is calculated as F = QE. So, if an electric charge E1 is created by Q1 and we have an electric charge Q2 in that field too, according to the Coulomb's Law the force that is applied to Q2 is equal to F2 = Q2E1 = Q1Q2/(4πε0r2). These forces being there means that the electric field has both magnitude and direction.
Now, the movement of charges are called Current i(t), and it is defined to be the opposite of the flow of electrons (from positive to negative terminal). Current is shown in amperes (A) and is calculated as the number of coulombs of charge in a given time (A = C/Sec). So it is a rate of transporting charges. The Current Density (ρ), also known as Volume Current Density (J) is the Density of Charge (number of particles times their charges) moving per unit of time through a volume. Please note that there is a magnitude and direction. Its direction is the direction of the velocity vector which depends on the moving forces moving and opposing the charge. The moving force is called Voltage or Electromotive Force, and the opposing force is called Impedance. So, J = ρv. The current perpendicular to a surface is determined by integrating the current density over that surface.
We know that a single charged object can have generate electric field, but a Magnetic Field is only generated when there is two objects (poles: north pole or Magnetic Source and south pole or Magnetic Sink) with opposite charges. Total number of Magnetic Flux in a magnetic field is shown by φ, and is measured in webers (Wb). Magnetic Flux Density, B, or Magnetic Induction is a vector and measured in teslas (T) which is the same as (Wb/m2) is how the strength of a magnetic field (B-field) is determined. So, B = φ / Area. The strength of a magnetic field is shown by H (A/m) and is derived from magnetic flux density. Direction of magnetic field is determined by the Right-Hand Rule. If the magnetic field is resulted by a straight wire, fingers curve around the wire shows the field direction, the thumb shows the current direction, while, if it is a coil, the fingers turn in the current direction and the thumb shows the magnetic field direction.
We can also use the concept of Voltage to to describe how strong an electric field is. Voltage is only in terms of magnitude and so therefore, we won't have any direction as we previously used for describing electric fluxes. The work required to move one unit charge between two points, is the Potential Difference (V). If 1 joule is used to move the unit charge (1 Coulomb), then the potential difference is 1 Volt. The change in this potential difference over a distance is called the Potential Electrical Gradient (V/m) and is the same as the strength of of the electric field (N/C, or V/m). So if there are two parallel plates with potential difference V are located at a distance d, the electric field between them is E = V / d.
Gauss' Law says that if we have a closed surface, the electric flux passing out of it is equal to the total charge within it. and that is where the Coulombs' Law can be derived from.
The Work (W) by moving a charge Q1 in its electric field for a distance is the product of charge and total force applied. Work is positive if an extrenal force is applied but if the electric field does the job, then work is negative. Bear in mind, that work is done always when the distance between the charges are changed. so moving around in a constant distance does not do work. Simple said, if a charge is moved perpendicular to an electric field, it won't do any work.
Similar to the electric field density depending on the permittivity of the material, magnetic field density also depends on the permeability of the material. Also, similarly, as in an electric field, force is imposed to a stationary charge, in a magnetic field, force is imposed to a moving charge. A wire carrying a current I is a uniform magnetic field B, is F = IL × B, where L is the length vector of the conductor and shows the current direction. A magnetic field can store the energy as well. It should be known that magnetic flux lines always follow a closed path which is the law of No Isolated Magnetic Charge or No Magnetic Monopoles. According to Faraday's Law of Induction, if there is a change in the magnetic flux in a circuit, an Induced Voltage, ʋ, or electromotive force is generated. This is an Electromagnetic Induction. According to the Lenz's Law, the direction of the induced voltage is the opposite of the direction of magnetic field. Next, is to learn about electric circuits.
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