Umair Gaines
Voltage, or electric potential, is a term used to describe the energy per unit charge required to move a test charge. It is measured in volts and compared to pressure in fluid flow. Voltage is also referred to as electric potential difference, commonly represented as EMF (electromotive force). While EMF is a term closely related to voltage, it specifically relates to the potential difference provided by a power source when there is no load attached.
| Characteristics | Values |
|---|---|
| Other term | Potential difference |
| Voltage definition | Quantity expressed in units of volts |
| Voltage definition | Difference of electric potential between two points |
| Voltage definition | Force that drives electric current through a conductor |
| Example | Battery |
| Measurement | Measured in volts (V) |
| Measurement | Represents the amount of energy per unit of charge |
| Use case | Used in batteries, power supplies, and electric outlets |
| Use case | Used to provide the necessary power for devices |
| Use case | Used in alternating current (AC) and direct current (DC) |
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What You'll Learn
Electric potential
The voltage drop across a device is the difference between measurements at each terminal of the device with respect to a common reference point (or ground). Two points in an electric circuit that are connected by an ideal conductor without resistance and not within a changing magnetic field have a voltage of zero. The various voltages in a circuit can be computed using Kirchhoff's circuit laws.
When discussing alternating current (AC), it is important to distinguish between instantaneous voltage and average voltage. Instantaneous voltages can be added for both direct current (DC) and AC, but average voltages can only be added when they apply to signals with the same frequency and phase.
The term "electric potential" is related to the concept of electromotive force (emf), which was first used by Volta in the late 18th century. Volta distinguished emf from tension (potential difference), observing that the potential difference at the terminals of an electrochemical cell in an open circuit must balance the emf to prevent current flow.
In conductive materials, the energy of an electron is influenced not only by the average electric potential but also by the specific thermal and atomic environment. When a voltmeter is connected between two different types of metal, it measures the negative difference of the electrochemical potential of electrons (Fermi level) divided by the electron charge, commonly referred to as the voltage difference.
In summary, electric potential, or voltage, is a crucial concept in electrical circuits, representing the force that drives electric current and powering various devices in our daily lives.
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EMF (electromotive force)
The term electromotive force (EMF) was first used by Alessandro Volta in a letter to Giovanni Aldini in 1798, and it first appeared in a published paper in 1801. The term was later taken up by Michael Faraday in connection with electromagnetic induction in the 1820s.
EMF is an energy transfer to an electric circuit per unit of electric charge, measured in volts. Devices called electrical transducers provide an EMF by converting other forms of energy into electrical energy. For example, a generator or a battery is used for the conversion of energy from one form to another. In these devices, one terminal becomes positively charged while the other becomes negatively charged.
EMF is not a physical force, and ISO/IEC standards have deprecated the term in favor of source voltage or source tension. However, it is still commonly used to refer to the electric potential produced by either an electrochemical cell or by changing the magnetic field.
There are two types of EMF: statically induced and dynamically induced. When the conductor is moved in a stationary magnetic field to procure a change in the flux linkage, the EMF is statically induced. When the change in flux linkage arises from a change in the magnetic field around the stationary conductor, the EMF is dynamically induced.
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Voltage drop
In electronics, voltage drop refers to the decrease in electric potential along the path of a current flowing in a circuit. It is caused by the resistance of the wire, which creates a “contrary pressure” that results in a loss of electrical potential or voltage. This phenomenon is undesirable as it leads to energy dissipation, with a portion of the supplied voltage being lost in the wire itself.
The voltage drop can be calculated using Ohm's Law, which states that voltage drop is equal to the product of current and resistance (V = IR). In an AC circuit, electrical impedance, a combination of resistance and reactance, is used in the formula (E = IZ). The voltage drop is influenced by various factors such as wire length, wire size, and the amount of current being carried. For instance, shorter wires and larger wire sizes exhibit lower voltage drops.
The maximum acceptable voltage drop differs across countries and is regulated by national and local electrical codes. Exceeding this threshold can cause issues such as flickering lights, poorly performing heaters, and motors operating at higher temperatures. To mitigate excessive voltage drop, techniques like increasing the diameter of the conductor or employing active elements are utilized.
The term "voltage" itself has evolved over time. While it initially referred to the difference in electric potential between two points, it now encompasses a broader definition that includes the electric potential and the line integral of the electric field. "Potential difference" is another term used interchangeably with voltage, emphasizing the disparity in electric potential.
Understanding voltage drop is crucial in electrical engineering to ensure the efficient distribution of power and the proper functioning of electrical devices. By considering factors like wire material, length, and current load, voltage drops can be managed to prevent performance issues and maintain the safety of electrical systems.
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Galvani potential
In electrochemistry, the Galvani potential, also known as the Galvani potential difference or inner potential difference, is the electric potential difference between two points in the bulk of two phases. These phases can be two different solids, such as two metals joined, or a solid and a liquid, such as a metal electrode submerged in an electrolyte. It is named after Luigi Galvani.
When two metals are electrically isolated from each other, there may be an arbitrary voltage difference between them. However, when two different metals are brought into electronic contact, electrons will flow from the metal with a lower voltage to the one with a higher voltage until the Fermi level of the electrons in both phases is equal. The actual number of electrons that pass between the two phases depends on the capacitance between the objects.
The electrochemical potential of a species is defined as the sum of its chemical potential and the local electrostatic potential. The difference between the phases is the Galvani potential difference. This difference is determined entirely by the chemical difference between the two phases, specifically by the difference in the chemical potential of the charge carriers in the two phases. The Galvani potential difference between an electrode and an electrolyte forms in a similar way, although the chemical potentials in the equation may need to include all species involved in the electrochemical reaction at the interface.
The Galvani potential difference is not directly measurable using voltmeters. It is different from the measured potential difference between two metal electrodes assembled into a cell, which does not equal the difference in the Galvani potentials of the two metals. The Galvani potential is related to the electrochemical potential, which can be directly measured with a voltmeter.
In summary, the Galvani potential refers to the electric potential difference between two points in the bulk of two phases, typically two different solids or a solid and a liquid. It is a concept in electrochemistry, named after Luigi Galvani, and it plays a crucial role in understanding the behaviour of electrons and electrochemical reactions.
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Electrochemical potential
In the context of electric voltage, electrochemical potential is a crucial concept. Electrochemical potential, often abbreviated as ECP, is a thermodynamic measure of chemical potential that accounts for the energy contribution of electrostatics. It is expressed in the unit of J/mol, representing the energy per mole of ions.
In simpler terms, electrochemical potential describes the mechanical work required to bring one mole of an ion from a standard state to a specific concentration and electrical potential. This concept is particularly relevant in electrochemistry and solid-state physics, where it helps us understand the behaviour of electrons and ions.
The electrochemical potential is influenced by the chemical potential and the electrical potential. Chemical potential, as seen in the example of sugar molecules, is higher in regions of higher concentration, and molecules tend to move towards regions of lower chemical potential. Electrical potential, on the other hand, refers to the voltage or electric potential difference between two points.
In a galvanic cell, the difference in electrochemical potential between the anode and cathode leads to a spontaneous flow of electrons from the higher potential energy to the lower one, generating an electric current. This principle is fundamental to understanding batteries and fuel cells, where the electrochemical potential drives the flow of electrons to produce electricity.
Additionally, electrochemical potential is important in biological processes involving molecular diffusion across membranes. It also has applications in electroanalytical chemistry, such as measuring the concentration of H+ ions in a solution using a glass electrode.
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Frequently asked questions
Electric voltage is often referred to as the 'potential difference'.
Potential difference is the difference in electric potential energy between two points in a circuit.
Other terms for potential difference include 'resistance', 'energy', 'work', and 'charge'.
