What is the electromotive force?

In this paper we will talk about what is the electromotive force of a current source and what is its relationship with other parameters of an electrical circuit. Just note, despite the fact that in everyday life we all successfully use electrical appliances, many laws were derived by experience and taken for an axiom. This is one of the reasons for unnecessarily complicating definitions. Unfortunately, even electromotive force, this basis of electrical engineering, is illuminated so that a person unfamiliar with electricity can understand something quite difficult. We will explain this question with the help of understandable terms and examples.

The directional motion of charged particles in a conductor is called "electric current". As you know, all the objects of our material world are made up of atoms. To simplify understanding, we can assume that each atom is represented in the form of a model of the solar system reduced in millions of times : in the center there is a nucleus, and at different distances from it in the circular orbits the electrons rotate.

By means of some external action, an electromotive force is generated in the conductor forming a closed loop and an electric current is generated. The action "knocks out" the valence electrons from their orbits in atoms, so free electrons and positively charged ions are formed.

The electromotive force is necessary in order to "force" the charges to constantly move along the conductor and the elements of the chain in a certain direction. Without it, the current almost instantaneously fades. Understand what is an electromotive force, will allow comparison of electricity with water. The straight section of the pipe is the conductor. Two of its sides, it goes into the water. Until the water levels in the reservoirs are equal and there is no slope, the liquid in the pipe is stationary.

Obviously, you can make it move in three ways: create a height difference (slope or the amount of fluid in the reservoirs) or forcefully pump. An important point: if we talk about the difference in height (the potential difference), then the stress is implied. For EMF, the movement is "compulsory", since the external forces that influence are non-potential.

Any source of electric current has an EMF - the same force that supports the motion of charged particles (in the above analogy it forces water to move). It is measured in volts. The name speaks for itself: the EMF characterizes the operation of external forces applied to the circuit, performing the movement of each unit charge from one pole to the other (between the terminals). It is numerically equal to the ratio of the work of the applied external forces to the value of the transferred charge.

Indirectly, the need for an EMF source can be derived from the law of conservation of energy and the properties of a conductor with a current. In a closed circuit, the work of the field with respect to charge transfer is zero. However, the conductor heats up (and the stronger, the greater the current passes through it per unit time). Conclusion: the share of external energy should be present in the circuit. These third-party forces are a magnetic field in generators, constantly exciting electrons; Energy of chemical reactions in batteries.

The electromotive force of induction was first discovered experimentally in 1831 by physicist Faraday. He found that an electric current is generated in a conductor permeated by lines of tension of a changing magnetic field. The effect of the field informs the external electrons in the atoms of the missing energy, as a result of which they break away and begin to move (a current appears). Of course, there is no direct movement of the particles (how can one not remember the relativity of the axioms of electrical engineering). Rather, there is an exchange of particles between the nearest atoms.

Developed electromotive force is an internal characteristic of any power source.