Electrotechnics: Basics


Electric field intensity

Force of the generated electric charges

Electric field intensity is a vector quantity, and therefore has a numerical value and direction. The electric field has a dimension that depends on the method of its calculation.

The electric force of interaction between charges is described as a non-contact action, and that is to say there is a long-range action, that is action at a distance. In order to describe a long-range convenient to introduce the concept of the electric field and use it to explain the action at a distance.

Let's take an electrical charge, which we denote by Q. Is this an electrical charge creates an electric field, that is, it is the source of the force. Since in the universe there is always at least one positive and at least one negative charge, which acts on each other at any even infinitely far away, any charge is a source of strength, and therefore appropriate description of the electric field generated. In this case, the charge Q is the source of the electric field, and we consider it just as a source of the field.

test charge

The electric field of the source charge can be measured by any other charge, located somewhere in the vicinity. The charge, which is used to measure the electric field is called the probe charge, since it is used to test the strength of the field. The probe charge has a certain amount of charge denoted by the symbol q.

When you move a probe charge in an electric field power source (charge Q), the probe charge will experience the action of the electric force - or the attraction or repulsion. Force can be defined as it usually take physics symbol F. Then the electric field can be defined simply as the ratio of the force to the magnitude probe charge.

expression E = F\\q

If the electric field denoted by the symbol E, then the equation can be written in symbolic form as:

equation electric field intensity

The standard metric units of measure the electric fields arise from its definition. Thus, the electric field is defined as the force is equal to 1 Newton (N) divided by the 1 Coulomb (C). Electric field intensity is measured in Newton/Coulomb anyway H/C. The SI also measured in volts/meter. To understand the essence of the subject as the electric field is much more important dimension in the metric system in the H/C, because in this dimension reflects the origins of such features as field intensity. Designation in the voltmeter does the concept of potential field (V) base, which in some areas is convenient, but not all.

The following example involves two charges Q (the sources) q probe. Both of these charges are a source of strength, but which one should be used in the formula? In the formula, there is only one charge, and it is the probe charge q (not the source).

Electric field intensity does not depend on the number of probe charge q. At first glance, it can lead you into confusion, of course, if you think about it. The problem is that not everyone has a useful habit to think and remain in the so-called blissful ignorance. If you do not think that this kind of confusion, and you do not arise. Since the electric field intensity is independent of q, q if present in the equation? Great question! But if you think about it a little, you will be able to answer this question. Increasing the number of probe charge q - say, 2 times - to increase and the denominator of the equation 2 times. But according to Coulomb's law, the increase in the charge will also increase proportionally and generates a force F. Charge increase by 2 times, then the force F increases to the same number of times. Since the denominator in the equation is doubled (or three or four), the numerator will increase by the same factor. These two changes cancel each other, so we can safely say that the electric field does not depend on the number of probe charge.

Thus, no matter how many the probe charge q is used in the equation, the electric field E at any given point around the charge Q (source) will be the same when measured or calculated.

For more information about the equation the electric field intensity

We have touched on the definition the electric field intensity in the way it is measured. Now we will try to explore more unfolded equation with variable to a clearer understanding of the essence of calculation and measurement the electric field intensity. From the equation we can see that it affects and what is not. To do this, we first need to return to the equation of Coulomb's law.

Coulomb's law states that the electric force F between two charges is directly proportional to the multiplication of quantities of these charges and inversely proportional to the square of the distance between their centers.

If you enter into the equation of Coulomb's law, our two charge Q (source) and q (probe charge), then we get the following entry:

Equation of Coulomb's law

If the expression for the electric force F, as defined by Coulomb's law to substitute the equation for the electric field intensity E, which is shown above, then we obtain the following equation:

Equation the electric field intensity

Note that the probe charge q has been reduced, that is removed in both the numerator and denominator. The new equation for the electric field E expresses the intensity of the field in terms of two variables which affect it. The electric field is dependent on the amount of initial charge Q and the distance d from this charge to a point in space, i.e. the locus, and wherein the determined value of tension. Thus we have been able to characterize the electric field via its tension.

Inverse square law

Like all the equations of physics, the equation for the electric field can be used for solving algebraic problems (problems) physics. Just like any other algebraic equation in its entries can be examined, and the equation of the electric field. This study contributes to our understanding of the physical essence of the phenomenon and the characteristics of the phenomenon. One of the characteristics equation of the field strength is that it illustrates the relationship between the inverse square electric field strength and the distance to the point in space from the field source. Force of the electric field generated at the source of the charge Q is inversely proportional to the square of the distance from the source. In other words, the unknown quantity that is inversely proportional to the square.

Electric field intensity depends on the geometrical place in the space, and its value decreases with increasing distance. For example, if the distance is increased by 2 times, the tension is reduced by 4 times (22), if the distance between the decrease in 2 times, then electric field intensity will increase by 4 times (22). If the distance is increased to 3 times, the electric field intensity is reduced by 9 times (32). If the distance is increased 4 times, the electric field intensity decreases at 16 (42).

Direction the electric field vector

As mentioned above, the electric field is a vector quantity. In contrast to the scalar, vector quantity is not fully described, if not defined its direction. The magnitude of the electric field is calculated as the amount of force on any the probe charge within the electric field.

The force exerted on a probe charge can be directed to either a charge source or directly from it. The exact direction of the force depends on the signs of the charge and the trial charging source, whether they have the same sign of charge (while going repulsion), or their opposite signs (there is an attraction). To solve the problem of the direction of the electric field vector, it is directed to the source or the source of the rules have been adopted, which are used by scientists all over the world. Under these rules, the direction vector is always on the charge of positive polarity sign. This can be represented as power lines that go from the positive signs of the charges and the charges come in negative signs.

Date: 01.28.2016

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© Valentin Grigoryev


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