What is an internal voltage EMF

Difference Between EMF and Voltage

EMF (Electromotive Force) is the voltage at the ends of a source when there is no current. When the circuit is closed and a current is flowing, there is a voltage at the ends of the source that is less than the EMF. This is a consequence of the internal resistance of the source itself, which leads to this voltage drop.

What is EMF?

Electrically charged bodies can be obtained by separating electrons from atoms by consuming some other kind of energy, e.g. mechanical, light or chemical. One such separation is in electrical sources. Due to the energy activity in the source, an EMF is created which also induces an excess of negative charge (negative pole) and a lack of negative charge (positive pole). In electrical engineering, the concept of EMF defines the work required to separate the charge carriers in an electrical power source where the force acting on the charges at the ends of the source is not a direct result of the field. EMF is defined as the work performed (A) in energy transformation and the amount of electricity (Q) flowing through the generator E = A / Q. The unit corresponds to the voltage (V-Volt). The device that supplies electrical energy to the circuit and creates an electromotive force is known as an electromotive force source, or shorter EMS (electromotive source).

What is tension?

The electrical states at the poles (terminals) of the source differ. There is an excess of electrons on the negative pole and an electron deficiency on the positive. In a closed circuit, electrons move from the negative to the positive half through conductors and devices. The difference between the electrical potentials is called the electrical voltage [U]. The electrical voltage is equal to the amount of work that the electrical force does in moving the charge from one point in the field to another and this charge. The electrical voltage is measured in volts [V]. The voltage measuring device is called a voltmeter.

Difference Between EMF and Voltage

  1. definition

Electromotive force refers to the voltage generated in the electrical sources. Voltage is defined as the difference in electrical potential between two points, and this difference at the poles of the electrical source is obtained by removing electrons from one part of the source and transferring them to another.

  1. Expression

The source electromotive force is equal to the work that an external force must do to move the charging unit from one pole of the source to another, but through the source. The voltage in the outer part of the circuit largely corresponds to the work that must be done by the electrical force to move the charging unit from one pole of the source to the other, but through the wire.

  1. formula

The electromotive force is calculated as follows: E = I * (R + r). Voltage is calculated V = I * R (I - flowing current, R - load resistance, r - internal resistance).

  1. Electric power operation

The voltage is an operation of the electric (coulomb) force in the movement of the charge and is the result of a decrease in energy in the circle, while the electromotive force is defined by a non-electric force (non-coulomb) operation and is responsible for the increase in energy in the circuit.

  1. Measurement

A potential difference (voltage) can be measured between any point in the circuit, while the electromotive force is only present between the two ends of a source. The electromotive force is also measured with an EMF meter, while the voltage is measured with a voltmeter.

  1. intensity

The electromotive force is always greater than the voltage. This is because the voltage is present in a loaded circuit and there is a voltage drop due to the resistance (loss of energy). The strength of EMF is always constant, while the voltage intensity is different.

  1. induction

EMF can occur in electrical, gravitational or magnetic fields, while voltage occurs only in electrical fields.

EMF vs. voltage


  • The quantity that adequately represents the generator as an element of the electrical circuit and quantitatively characterizes its ability to maintain the current in the circuit and to convert other forms of energy into an electrical one is known as the electromotive force. In order for the source to have a pole potential difference, the electrons must be "moved" from one pole to another, ie a process of charge separation is required. Work performed on a unit of charge by an external force by dividing the charges at the source of electric power is called an electromotive force. The electromotive force (EMF) has a voltage dimension (volt unit) and is also referred to as the internal voltage of the source (U0). The electromotive force has the same magnitude as the potential difference between the positive and negative generator connections when it is idle.
  • The potential difference between two points of the electric field is called voltage, and the unit is also volt. The electrical voltage is the cause of the flow of electrons in the circuit to the (-) negative pole with excess electrons, to the (+) positive pole with electron defect - the electrons move from the (-) half to the (+) pole.