In this paper, we will talk about what is the electromotive force of the current source and what is its relationship with other parameters of the electric circuit. We note right away, despite the fact that in everyday life we all successfully use electrical appliances, many laws were derived experimentally and taken for an axiom. This is one of the reasons for unnecessarily complicated definitions. Unfortunately, even the electromotive force, this foundation of electrical engineering, is illuminated in such a way that it is rather difficult for a person unfamiliar with electricity to understand anything. Let us explain this question with the help of terms and examples that are clear to everyone.
The directional movement of charged particles in a conductor is called "electric current." As you know, all objects of our material world are composed of atoms. To simplify the understanding, we can assume that each atom is represented in the form of a model of the solar system reduced by a million times : the core is located in the center, and at different distances from it, electrons rotate in circular orbits.
Through any external action in the conductor, forming a closed loop, an electromotive force is created and an electric current occurs . The action “knocks out” valence electrons from their orbits in the atoms, so free electrons and positively charged ions are formed.
An electromotive force is necessary in order to “force” the charges to constantly move along the conductor and circuit elements in a certain direction. Without it, the current fades almost instantly. To understand what electromotive force is, a comparison of electricity with water will allow. A straight section of the pipe is a conductor. With its two sides it goes into the ponds. As long as the water levels in the reservoirs are equal and there is no slope, the fluid in the pipe is stationary.
Obviously, you can make it move in three ways: create a height difference (by slope or the amount of liquid in the water) or force pumping. An important point: if we talk about the height difference (potential difference), then voltage is implied. For EMF, the movement is “forced”, since external forces exerting influence are not potential.
Any source of electric current has an EMF - the same force that supports the movement of charged particles (in the above analogy, it makes water move). Measured in volts. The name speaks for itself: EMF characterizes the work of external forces applied to a section of the circuit that carry out the movement of each unit charge from one pole to another (between the terminals). It is numerically equal to the ratio of the work of the applied external forces to the magnitude of the charge transferred.
Indirectly, the need for a source of EMF can be deduced from the law of conservation of energy and the properties of a conductor with current. In a closed circuit, the work of the field in the movement of charges is zero. However, the conductor heats up (and the stronger it is, the more current passes through it per unit time). Conclusion: there must be a fraction of external energy in the circuit. The indicated third-party forces are a magnetic field in generators that constantly excites electrons; energy of chemical reactions in batteries.
The electromotive force of induction was first discovered experimentally in 1831 by the physicist Faraday. He established that an electric current arises in a conductor penetrated by lines of intensity of a changing magnetic field. The effect of the field tells the external electrons in the atoms the energy they need, as a result of which they come off and begin to move (a current appears). Of course, there is no direct movement of particles (how can one not recall 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.