Electromotive force (EMF) is the energy per unit of charge that is provided by a source, such as a battery or generator, to drive a current through a circuit. EMF is measured in volts (V) and is symbolized by the letter “E” or “ε” .
In a circuit, the EMF is the source of energy that drives the current flow. When a circuit is closed, the EMF causes the current to flow from the positive terminal of the source, through the circuit, and back to the negative terminal of the source.
However, it is important to note that the EMF is not the same as the voltage that is measured across the circuit. This is because some of the energy provided by the source is lost as the current flows through the circuit, due to the resistance of the circuit elements, such as wires, resistors, and other components.
The voltage that is measured across the circuit is called the potential difference (PD) and is measured in volts as well. The PD is the difference in electric potential between two points in the circuit, and is the amount of energy per unit charge that is lost as the current flows through the circuit.
In summary, EMF is the source of energy that drives the current flow in a circuit, while the PD is the voltage that is measured across the circuit and is the amount of energy per unit charge that is lost as the current flows through the circuit. Both EMF and PD are measured in volts, but they represent different aspects of the circuit.
An electronic–hydraulic analogy may view emf as the mechanical work done to water by a pump, which results in a pressure difference (analogous to voltage).
Methods of producing EMF
There are several methods of producing EMF, which is the energy per unit of charge that is provided by a source to drive a current through a circuit. Some of the most common methods are:
- Chemical reaction: This is the most common method of producing EMF, and it is used in batteries. Chemical reactions in the battery generate a potential difference between the two electrodes, which drives the current flow.
- Electromagnetic induction: This method of producing EMF is based on Faraday’s law of electromagnetic induction. When a magnetic field is changed, it induces an electric field, which can produce an EMF. This is the principle behind generators and transformers.
- Thermoelectric effect: This method of producing EMF is based on the Seebeck effect, which occurs when two dissimilar metals are joined at different temperatures. The temperature difference generates an EMF that can drive a current flow.
- Photoelectric effect: This method of producing EMF is based on the fact that some materials emit electrons when exposed to light. This effect is used in solar cells, where the photons from the sun excite electrons in the material, generating an EMF that drives a current flow.
- Piezoelectric effect: This method of producing EMF is based on the fact that some materials generate an EMF when subjected to mechanical stress, such as pressure or vibration. This effect is used in sensors and actuators.
In summary, EMF can be produced by chemical reactions, electromagnetic induction, thermoelectric effect, photoelectric effect, and piezoelectric effect. Each method has its own unique characteristics and applications, and is used in various devices and systems.
EMF and potential difference
EMF (Electromotive Force) and potential difference (PD) are two related but distinct concepts in electricity. Both EMF and PD are measured in volts, but they represent different aspects of a circuit.
EMF is the energy per unit charge that is provided by a source, such as a battery or generator, to drive a current through a circuit. EMF is the maximum possible voltage that a source can provide, and it is equal to the work done by the source in moving a unit charge from one terminal to the other. EMF is often referred to as the “voltage” of the source.
On the other hand, potential difference (PD) is the voltage that is measured across a circuit element, such as a resistor or a wire. PD is the difference in electric potential between two points in the circuit, and it is equal to the work done per unit charge in moving a charge from one point to the other. PD is also called voltage drop.
In other words, while EMF is the maximum voltage that a source can provide, PD is the voltage that is actually present in the circuit due to the resistance of the circuit elements. As the current flows through the circuit, some of the energy provided by the source is lost due to the resistance of the circuit elements, resulting in a lower voltage across the circuit elements.
In summary, EMF is the maximum possible voltage that a source can provide, while PD is the voltage that is actually present in the circuit due to the resistance of the circuit elements.
