Coulomb's law is a law of physics describing the electrostatic interaction between electrically charged particles. Was formulated and first published in $1783$ by French physicist Charles Augustin de Coulomb and was essential to the development of the study of electricity. This law states that the magnitude of the force between two punctate electrical charges ($q_1$ and $q_2$) is directly proportional to the product of the absolute values (modules) of the two charges and inversely proportional to the square of the distance r between them. This force can be attractive or repulsive depending on the sign of the charges. It is attractive if the charges have opposite signs. It is repulsive if the charges have the same sign.

Diagram depicting the basic mechanism of Coulomb's law. The like charges repel and opposite charges attract Once detailed measurements using a torsion balance, concluded that the Coulomb force is fully described by the following equation:

Where :

$(N)$

Is the Force In Newtons$C^2 N^{-1} M{-2}$ Is the Permittivity of free space

$r$ Is the Distance between the Two Point charges in Meters $(m)$ and $Q_1$ and $Q_2$, respective load values in Coulombs $(C)$ .

Is the Vector that Indicates the Direction in Which the Electric Force points.

Sometimes it replaces the factor $\frac{1}{4 \pi \epsilon_o }$ by $k$ , Coulomb's Constant, with $k$

The previous notation is a compact vector notation, which is not specified any coordinate system. If the load $1$ is the source and the load at point $2$ with Cartesian coordinates $(x, y, z)$ the Coulomb force takes the form:

How to charge a Coulomb (C 1) is very large, it is customary to use submultiples of this unit. Thus we have:

$1$ Milicoulomb = $10^{-3} C$

$1$ Microcoulomb = $10^{-6} C$

$1$ Nanocoulomb = $10^{-9} C$

$1$ Picocoulomb = $10^{-12} C$

Remembering that $C= 6,25 \times 10^{18}$ Electrons

Problem I

Two particles of electric charges

$Q = 4.0 × 10^ {-16} C$ and $q = 6.0 × 10^{-16} C$

vacuum are separated by a distance of $3,0 \times 10^{-9}m$.

Where $k = 9.0 \times 10^9$ , the intensity of the force of interaction between them, in newtons, Is :

$a) 1,2 \times 10{-5}$

$b) 1,8 \times 10{-4}$

$c) 2,0 \times 10^{-4}$

$d) 24 \times 10^{-5}$

$e) 30 \times 10^{-4}$

Solution :

$F = \frac{k \times Q_1 \times Q_2}{d^2}$

$F = \frac{9,0 \times 10^9 \times 4,0 \times 10^{-16} \times 6,0 \times 10^{ -16}}{(3,0 \times 10^{-9})^2}$

$F = \frac{9,0 \times 10^9 \times 4,0 \times 10^{-16} \times 6,0 \times 10^{-16}}{(3,0 \times 10^{-9} \times 3,0 \times 10^{-9})}$

$F = \frac{3,0 \times 10^9 \times 4,0 \times 10^){-16} \times 2,0 \times 10^{-16}}{10^{-18} }$

$F = \frac{24 \times 10^9 \times 10^{-16} \times 10^{-16}}{10^{-18} }$

$F = \frac{24 \times 10^{-23}}{10^{-18} }$

$F = \boxed{24 \times 10^{-5} N}$

You Can Watch these Videos for See More Examples:

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## Comments

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TopNewestReally well explained

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Thanks ! This Is Very Important for Me !

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Hello, try visiting http://sciencefront.webs.com for some cool science stuff for kids...

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very interesting

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interesting

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@Gabriel Merces Fix k in the example. It is not dimensionless.

$k=9.0\times{}10^{9} \frac{\text{ N m}^2}{\text{C}^2}$

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I wonder why they define $C=6.25\times10^{18}$ electrons. I mean for example there is a reason for $1\text{ mol}=6.02\times10^{23}$, but what about Coulomb? I hope I'm not asking silly questions...

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$1$ Coulomb is the Amount of Electric Charge carried by the Current of $1$ ampere per $1$ second.

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So I've just misunderstood the definition of Coulomb, Thanks!

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By the way, great note!

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@Christopher Boo Sorry this is off topic but how did you find brilliant squared? Satisfactory?

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i can't understand the coulomb force with cartesian coordinates

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