A point load, In the context of electromagnetism, it is that electrical charge of such small dimensions that it can be considered a point. For example, elementary particles that have electric charge, the proton and the electron, are so small that their dimensions can be omitted in many applications. Considering that a charge is point-oriented makes the job of calculating its interactions and understanding the electrical properties of matter much easier..
Elementary particles are not the only ones that can be point charges. So can ionized molecules, the charged spheres that Charles A. Coulomb (1736-1806) used in his experiments, and even the Earth itself. All can be considered point charges, as long as we see them at distances much greater than the size of the object..
Since all bodies are made of elementary particles, electric charge is an inherent property of matter, just like mass. You cannot have an electron without mass, and neither can it be without charge.
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As far as we know today, there are two types of electrical charge: positive and negative. Electrons have a negative charge, while protons have a positive charge..
Charges of the same sign repel, while those of the opposite sign attract. This is valid for any type of electrical charge, either punctual or distributed over an object of measurable dimensions..
In addition, careful experiments verified that the charge of the proton and that of the electron have exactly the same magnitude..
Another very important point to consider is that the electrical charge is quantized. To date, no isolated electric charges of a magnitude less than the charge of the electron have been found. They are all multiples of this.
Finally, the electric charge is conserved. In other words, electric charge is neither created nor destroyed, but it can be transferred from one object to another. In this way, if the system is isolated, the total load remains constant..
The unit for electric charge in the International System of Units (SI) is the Coulomb, abbreviated with a capital C, in honor of Charles A. Coulomb (1736-1806), who discovered the law that bears his name and describes the interaction between two point charges. We will talk about her later.
The electric charge of the electron, which is the smallest possible that can be isolated in nature, has a magnitude of:
and- = 1.6 x 10 -16 C
The Coulomb is quite a large unit, so submultiples are often used:
-1 milli C = 1 mC = 1 x 10-3 C
-1 micro C = 1 μC = 1 x 10-6 C
-1 nano C = 1 nC = 1 x 10-9 C
And as we mentioned before, the sign of and- is negative. The charge of the proton has exactly the same magnitude, but with a positive sign.
The signs are a matter of convention, that is, there are two types of electricity and it is necessary to distinguish them, therefore one is assigned a sign (-) and the other sign (+). Benjamin Franklin made this designation, and also enunciated the principle of conservation of charge..
By Franklin's time, the internal structure of the atom was still unknown, but Franklin had observed that a rod of glass rubbed with silk became electrically charged, calling this kind of electricity positive..
Any object that was attracted by said electricity had a negative sign. After the electron was discovered, it was observed that the charged glass rod attracted them, and this is how the charge on the electron became negative..
At the end of the 18th century, Coulomb, a French army engineer, spent a long time studying the properties of materials, the forces acting on the beams, and the friction force..
But he is best remembered for the law that bears his name and that describes the interaction between two point electric charges.
Let be two electric charges what1 Y whattwo. Coulomb determined that the force between them, either attraction or repulsion, was directly proportional to the product of both charges, and inversely proportional to the square of the distance between them..
Mathematically:
F∝ what1 . whattwo / rtwo
In this equation, F represents the magnitude of the force and r is the distance that separates the charges. Equality requires a constant of proportionality, which is called the electrostatic constant and is denoted as kand.
Thus:
F = k. what1 . whattwo / rtwo
Furthermore, Coulomb found that the force was directed along the line connecting the charges. Then yes r is the unit vector along this line, Coulomb's law as a vector is:
Coulomb used a device called torsion balance for your experiments. Through it it was possible to establish the value of the electrostatic constant in:
kand = 8.99 x 109 N mtwo/ Ctwo ≈ 9.0 x 109 N mtwo/ Ctwo
Next we will see an application. There are three point charges qTO, whatB and whatC that are in the positions indicated in figure 2. Let us calculate the net force on qB.
The load qTO attracts the load thatB, because they are of opposite signs. The same can be said about qC. The isolated body diagram is in figure 2 on the right, in which it is observed that both forces are directed along the vertical axis or y axis, and have opposite directions.
The net force on the charge qB it is:
FR = FAB + FCB (Principle of superposition)
It only remains to substitute the numerical values, taking care to write all the units in the International System (SI).
FAB = 9.0 x 109 x 1 x 10-9 x 2 x 10-9 / (2 x 10-two) two N (+Y) = 0.000045 (+Y) N
FCB = 9.0 x 109 x 2 x 10-9 x 2 x 10-9 / (1 x 10-two) two N (-Y) = 0.00036 (-Y) N
FR = FAB + FCB = 0.000045 (+Y) + 0.00036 (-Y) N = 0.000315 (-Y) N
These two forces have the same mathematical form. Of course, they differ in the value of the constant of proportionality and in that gravity works with masses, while electricity works with charges..
But the important thing is that both depend on the inverse square of the distance.
There is a unique type of mass and it is considered positive, so the gravitational force is always attractive, while charges can be positive or negative. Therefore, the electrical forces can be attractive or repulsive, depending on the case..
And we have this detail that is derived from the above: all objects in free fall have the same acceleration, as long as they are close to the surface of the Earth..
But if we release a proton and an electron near a charged plane, for example, the electron will have a much greater acceleration than the proton. In addition, the accelerations will have opposite directions.
Finally, the electric charge is quantized, just as it was said. That means that we can find charges 2.3 or 4 times that of the electron -or that of the proton-, but never 1.5 times this charge. The masses, on the other hand, are not multiples of some unique mass.
In the world of subatomic particles, the electric force exceeds the gravitational one in magnitude. However, on macroscopic scales, the force of gravity is the predominant one. Where? At the level of the planets, the solar system, the galaxy and more.
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