Electrodynamics is the physical study that underlies electricity. The name of this science refers to the combination of electrical charges (electro) and movement (dynamics). Electrodynamic knowledge favored the creation of essential devices in everyday life, such as lamps, showers and even electric cars.

In the following article, you will learn more about the three main concepts of electrodynamics: electrical resistance, electrical current and electrical power. Furthermore, better understand the relationship between Ohm’s Laws and this part of physics. Let’s go?

Electrodynamics Summary

In general, electrodynamics scholars observe the behavior of electrical charges in different media and materials and, based on this, are able to predict the distribution of electricity over time. 

At the junction between this knowledge and Ohm’s laws, tools were created that transform electrical energy into heat or light. In the following topics, we will better understand the main electrodynamic pillars.

Electric current

Electric current (i) is the physical quantity that measures the quantity of electrical charges that cross a conductor in a given space of time. In standard norms, dictated by the International System of Units, the value of i is expressed in Coulombs per second (C/s). But, in general, we call this unit an ampere, that is, 1 C/s = 1 A.

For example, if we observe the passage of 600 Coulombs in a conductor during one minute, what is the value of i?

To resolve this issue, you can use a rule of three:

600 Coulombs ———— 60 seconds 
x C ———– 1 second 

600.1 = 60.x
x = 10

We can then say that the electric current in question is i=10 C/s, or even, i = 10A.

From this reasoning, the formula for electric current was created, which is given by i = ΔQ/Δt. 

  • ΔQ is the variation in the amount of charge (Q f – Q i ) observed over the measured time. This magnitude is measured in coulombs; It is
  • Δt is the period of time in question (t f – t i ), given in seconds.

Electrical resistance

Electrical resistance is the physical concept that measures how much a given material is capable of preventing the passage of charges, that is, the flow of electrical current. 

This principle of electrodynamics is governed by Ohm’s Laws . Ohm’s first law relates the potential difference (U, measured in volts V), the electric current (i) and the resistance (R, measured in ohms Ω) observed in the medium, with the following formula:

R = U/i

Note that the mathematical expression implies that the greater the electric current, the lower the resistance offered by the material. At the same time, if the potential difference is very large, electrical charges will have greater difficulty traveling.

Ohm’s second law deals more with the characteristics of the material that offers resistance. With this, it is possible to notice that the longer a resistor is, the greater the difficulty it will be for electrical charges to pass through. At the same time, if the cross-sectional area of ​​the resistor is very large, the flow of current is facilitated.

The formula below equates this information, considering that ρ (read rô) is a specific characteristic of the material in question, regardless of its shape, size or surface area.

R = ρ. THERE 

  • R is the electrical resistance (Ω);
  • L is the length of the conductor (L);
  • A is the area of ​​the conductor (m 2 ); It is 
  • ρ: resistivity (Ω. m 2 ).

Joule effect

When a material is very resistant to the passage of electrical current, the physical disturbance caused by the passage of electrical charges generates heat. This phenomenon is called the Joule Effect and appears mainly in heating systems and devices.

Electric showers use a resistance inside the equipment. As water passes through this material, the resistivity of the material allows the Joule effect to occur, thus the liquid comes out heated. 

In this sense, there is a conversion of electrical energy into thermal energy, which can be greater or lesser depending on the efficiency of the equipment. See below the concepts and formulas of electrical power.

Electric power

Whenever we think about power, we remember the ability of a given object to perform its function. This definition is no different in electrodynamics. So, electrical power mathematically measures the capacity and efficiency that a device has to transform electrical energy into other forms of energy.

The general formula is given by the energy variation (ΔE) achieved in a given space of time (Δt): P= ΔE/Δt. This calculation is provided in the units of measurement Joules per second (J/s). In SI, these units may be called Watts (W).

There is also an electrodynamics formula that relates electrical power to the other pillars of electrodynamics, as you can see below:

P = i. U 

U = potential difference
i = electric current 
P = electric power

From this calculation, manipulations can be made with Ohm’s law formulas, so that electrical power is also obtained by:

P = i 2 .R
P = U 2 /R

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