As we know, the electric field plays the role of transmitter of interactions between electrical charges.
Imagine a point electric charge* Q in any region in space. This charge modifies the region that surrounds it, so that, when we place a test point charge q at a point P in that region, the existence of a force F, of an electrical nature, acting on q will be verified.
Likewise, the electric charge q produces an electric field that acts on Q.
The intensity of the electric field generated by a charge Q can be calculated by the equation:
k0 = 9×109 N.m2/C2 (electrostatic constant in vacuum)
Q = charge generating the electric field under study
d = distance between charge Q and point P.
The direction and direction of the electric field depend on the sign of the charge that generates this field.
If Q > 0, the electric field is moving away, and if Q < 0 the electric field is approaching.
It is common to hear the terms: Field of Attraction and Field of Repulsion, referring to the field of Approach and field of Removal, but that is a wrong notation and should not be used under any circumstances.
When the electric field is created by several fixed point charges, Q1, Q2, …, QN we can determine the electric field originated by these charges at any point P in space.
If Q1 were alone, it would give rise to the field vector in P, as well as Q2, alone, would give rise to a field vector in P and so on, up to QN which, alone, would generate the field vector.
The resulting electric field vector at point P, due to several charges, is the vector sum of the fields , , , where each partial vector is determined as if the respective charge were alone. I.e,
Let there be two charges +Q and –Q arranged in a vacuum as shown in the figure below:
It is known that the magnitudes of the charges are equal to Q. Therefore, calculate the intensity, direction and direction of the resulting electric field vector in P. Assume that Q = 2.10-6 C and that d = 0.3 m.
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Note that the charge + Q generates, in P, a REMOVAL electric field vector.
Also note that the charge – Q generates, in P, an APPROACH electric field vector.
As the charges are equidistant in relation to point P, the electric fields generated by them have the same intensity, direction and sense, like this:
Thus, the intensity of the resulting electric field is:
Its direction is horizontal and the direction is from left to right.
* Point electrical charge is an electrical charge that has negligible dimensions.
By Kléber Cavalcante
Graduated in Physics
Electricity – Physics –