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Introduction to electromagnetism

This post will explain basic electromagnetism concepts. Therefore is destined to beginners in the area.

Electrons

All matter is made of atoms. An atom is a particle organization with positive charges (protons), negative (electrons) and neutral (neutrons).

Electricity is about phenomenons which involve electrons and your moves. Neutral charges does not have neither lack or excess of electrons. Positive charges are charges with less electrons than the neutral equivalent, while negative charges have more electrons than the neutral equivalent. Evidently when more lack or excess of electrons, greater is the object’s charge.

Charges with equal signal repel each other and charges with opposite signal attract each other.

The Coulomb’s Law determine that the repulsion or attraction force between charges is inversely proportional to distance, in other words, closer, greater the force and further, lesser the force.

\large F=\frac{1}{4\pi \varepsilon _o}\frac{\left | q1 \right |\left | q2 \right |}{r^{2}}

F is the electrical force, d is the distance between the charges, q1 and q2 are charges values in coulomb (C), \varepsilon _o is the vacuum permissibility constant which value is 8,85\times 10^{-12} C^{2}/N\cdot m^{2}. You can also adopt is following constant:

\large k=\frac{1}{4\pi \varepsilon _{o}} = 8,99\times 10^{9} N\cdot m^{2}/C^{2}

Positive charges create divergent electrical field and negative charges create convergent electrical field.

Tension or potential difference

Every point in an electric field has a electric potential. Just like the electrical force is inversely proportional to the distance, but not at square of distance.

\large V=\frac{1}{4\pi \varepsilon _{o}}\frac{q}{r}

Potential difference between two points in an electrical field which is not in the same equipotential surface.

\large U=V_{1}-V_{2}

\large U=\frac{1}{4\pi \varepsilon _{o}}\frac{Q}{r_{1}}-\frac{1}{4\pi \varepsilon _{o}}\frac{Q}{r_{2}}

\large U=\frac{1}{4\pi \varepsilon _{o}}\frac{Q}{(d_{1}-d_{2})}

Potential difference is also called tension. When two points are linked with a conductor, it is created a current, which come from greater potential to the lesser. Actually the electron flux is in the opposite direction of current flux.

Why the current flux is in the opposite direction of the electron flux? The reason is that for a long time it was believed that the positive charges that moved, later they discovered that the electrons who move in the electrical current. “Positive” and “Negative” are arbitrary concepts to charges, could tell that the electrons have positive charge. For convection, it was considered that electrical current is charge flux and not particle flux.

Continuous current and alternate current

There are two types of current: continuous current and alternate current. Continuous current is constant in time, while the alternate vary in time and change direction periodically. In the figure we have continuous current in red and alternate current in blue.

Continuous current (CC) can be obtained with batteries and DC sources, while alternate current (CA) is obtained in the electrical outlet in homes.

Magnetism

There are two ways to produce magnetic fields: natural magnets and electrical current. An electrical current produce a magnetic field. \large \vec{B} is the magnetic field and \large \vec{I} is the current.

The direction of current and field are determined by the right hand’s rule.

Parallel currents in equal directions attract each other and parallel current with opposite directions repel each other.

Equation to calculate the force:

\large F_{12}=\frac{\mu _{0}LI_{1}I_{2}}{2\pi d}

L is the conductor length, I_{1} and I_{2} are current values, d is the distance between the conductors and \large\mu _{0} is the vacuum magnetic permeability which is \large 4\pi \cdot 10^{-7}\frac{T\cdot m}{A}.

Continuous current (DC) produce a magnetic field, alternate current (CA) produce a electromagnetic wave, which is a variation of electrical and magnetic fields.

 

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About Pedro Ney Stroski

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