Tools
Electric Potential and Capacitance
Definition/Introduction
The Concept of Charge
Electric potential and capacitance originate from the concept of charge. The charge is determined by comparing the number of protons and electrons present in a material. A net positive charge indicates more protons than electrons. Conversely, a net negative charge denotes more electrons than protons. An equal number of protons and electrons indicates a neutral charge. Materials with charge also exhibit electrical forces—opposite charges attract (for example, positive and negative) and similar charges repel (for example, positive and positive or negative and negative). The unit of measurement for the charge is a coulomb (C). Protons and electrons have a charge of +1 or +1.602×10−19 coulombs and −1 or −1.602×10−19 coulombs, respectively. These charge values are considered the elementary charge because the accumulation of microscopic electrons and protons determines the macroscopic charge of the material. This concept is pertinent when considering polymers comprised of several materials whose compositions are studied under an electric field.[1][2]
Electric Potential: The Ability to Work on Charge
The work done on moving charges is the electric potential. As the name suggests, electric potential measures the change in the potential energy of a specific charge. The unit for electric potential is joules per coulomb (J/C), which measures the amount of work per charge. The J/C unit is commonly called a volt (V) and is the ubiquitous unit for electric potential. The concept of electric potential is often compared to that of gravitational potential energy. The higher an object is from the ground, the more gravitational potential energy it has. Similarly, the farther an object is from a charge, the more the electric potential is available. The electric potential from a specific charge is known as a point charge and can be measured explicitly.
The equation to determine the electric potential from a specific point charge is: V=κ·q/(r·r)
where V is the electric potential (V); κ is a constant measuring the inverse of the free space permittivity, often denoted as 8.99 E 9 N (m·m)/(C·C); q is the charge of the point (C); and r is the distance from the point charge (m), which is squared. Dimensional analysis is often required to ensure that all the units used in the equation are consistent. The electric potential is inversely related to the square of the distance from the point charge, suggesting that the farther an object is from the point charge, the more quickly the electric potential decays. In addition, if the electric potential is measured at various points around the object, a curve can be generated around the object where each point has the same potential. If 2 objects containing charges are placed next to each other, the attractive or repulsive force is present. This phenomenon is commonly represented by lines originating from the positively charged source with an arrow pointing to and terminating at the negatively charged source to denote the movement of charge.[3]
Capacitance: The Ability to Store Charge
Although electric potential measures the ability to perform work on a charge, capacitance measures the ability to store charge. The unit of measurement for capacitance is coulomb per voltage (C/V), representing the amount of charge present per voltage applied. The farad (F) is the standard unit for capacitance commonly used instead of C/V. A capacitor is used to hold capacitance and is created when 2 plates are parallel, with each end connected to opposite charge sources. Each charge fills 1 of the parallel plates, generating an electric field between the 2 plates. The capacitor can then discharge the charges between the 2 plates when connected.
The equation to determine the capacitance is: C=(κ·ε0·A)/d
where C is the capacitance (F), ε0 is the permittivity of free space (8.85 E −12 F/m), κ is the relative permittivity of the dielectric material between the plates, A is the geometric area of both plates (m·m), and d is the distance between the 2 plates (m). The capacitance is inversely proportional to the distance; therefore, the greater the separation between the 2 plates, the smaller the capacitance available. In addition, the κ-value is determined by the material between the parallel plates and is directly proportional to the capacitance; consequently, most capacitors have a solid material to improve capacitance.[4][5][6]
Issues of Concern
Register For Free And Read The Full Article
Search engine and full access to all medical articles- 10 free questions in your specialty
- Free CME/CE Activities
- Free daily question in your email
- Save favorite articles to your dashboard
- Emails offering discounts
Learn more about a Subscription to StatPearls Point-of-Care
Issues of Concern
These principles enable the design process when considering electrical potential and capacitance theories. However, several issues arise in the trial and error of selecting materials that adhere to theory and in reproducing the results, which are rooted in current research.
From Theory to Application
Electric potential and capacitance have many applications in power generation and energy storage. Every electrical appliance relies on the charge, electric potential, and capacitance function effectively. In a study by Roy et al, aspects of electric potential and capacitance were investigated concerning photogenerated electrical energy to enhance energy storage devices. In this work, Roy et al studied the capacitance of storage cells because capacitors are temporary batteries that hold a charge. However, capacitance is just one aspect of circuitry required to create effective electrical devices. Other aspects, such as current and resistance, are also integral for continuous electrical circuitry. Understanding a system's electric potential can create novel materials. Electrochemical engineering heavily relies on the accuracy of electric potential in fuel cells and batteries to maintain power distribution. By harnessing electric potential, for example, polymerization leads to discoveries such as bone regeneration or polymer interfaces to manufacture novel devices.[7][8][9][10]
From Application to Reproduction
The main concern with electric potential is the rigor with multiple-point charges. The electric potential can be a hindrance in many electrochemical-based studies. For example, water electrolysis occurs at 1.23 V, meaning that if more than 1.23 V is applied to a water system, the water molecules split into hydrogen and oxygen. Other molecules have voltage thresholds that must be considered when applying a voltage to a system. Another critical concern involves selecting the proper material for a capacitor. If a material exhibits excessive capacitance, it can lead to the destruction of the electrical application upon discharge. Conversely, insufficient capacitance renders the application ineffective. If the material is not sustainable, the capacitors may discharge, impacting economic value. When considering biocompatibility, these challenges represent any human-machine interface, such as irritation to human skin, resistance to environmental fluctuations, and durability to bodily secretions.[11][12][13]
Clinical Significance
Biological Applications
Electric potential is found in the human brain, where human neurons have an average voltage of 70 mV. Capacitance is found biologically in the plasma membrane and differentiates multiple stem cell lineages, measured by electrophoresis. In electrochemistry, a similar environment is described as an electric double layer, where ions group together based on the internal and external net charges. Based on biophysics, the electrical potential energy facilitates work within the human body.[6][14][15]
Technological Applications
A few technological applications are highlighted below.
- Electrical biosensors: These sensors are employed to detect biomarkers in bodily fluids using techniques such as capacitive sensing.
- Defibrillators: Capacitors within defibrillators are temporary batteries capable of discharging rapidly compared to regular batteries, which is imperative when a patient undergoes cardiac arrest.
- Electrorheological suspensions: This insulating fluid contains electroresponsive particles. These particles find wide applications in devices such as dampers, shock absorbers, and tactile displays, exhibited by several polymers under study.
Nursing, Allied Health, and Interprofessional Team Interventions
Healthcare professionals often encounter devices that operate based on electrical potential, ranging from diagnostic equipment to therapeutic tools. While the direct application of capacitance might not always seem pertinent to their daily clinical routines, understanding the relationship between electrical potential and capacitance is essential. This familiarity contributes significantly to ensuring electrical safety in medical settings. Moreover, grasping these concepts enables healthcare professionals to connect principles of electric potential and capacitance with fundamental physiological processes, thus enhancing their comprehension of clinical medicine.
Innovations in biotechnology are continuously shaping the landscape of modern healthcare, and clinicians involved in such advancements must possess a solid understanding of electrical principles. Whether they are designing new medical devices or exploring novel treatment modalities, knowledge of electric potential and capacitance provides a valuable foundation. Additionally, healthcare professionals engaged in research benefit greatly from these concepts.
Further research is imperative to explore the full potential of electric potential and capacitance in diagnostic and therapeutic applications. Currently, promising areas of study include the utilization of these concepts in urinalysis and hemodialysis. By expanding our understanding and leveraging these principles effectively, clinicians can unlock innovative approaches to diagnosis and treatment, ultimately improving patient care and outcomes in clinical practice.[17][18]
References
Balzer C, Wang ZG. Electroresponse of weak polyelectrolyte brushes. The European physical journal. E, Soft matter. 2023 Sep 14:46(9):82. doi: 10.1140/epje/s10189-023-00341-3. Epub 2023 Sep 14 [PubMed PMID: 37707751]
Gallegos A, Ong GMC, Wu J. Ising density functional theory for weak polyelectrolytes with strong coupling of ionization and intrachain correlations. The Journal of chemical physics. 2021 Dec 28:155(24):241102. doi: 10.1063/5.0066774. Epub [PubMed PMID: 34972389]
Komorek P, Jachimska B, Brand I. Adsorption of lysozyme on gold surfaces in the presence of an external electric potential. Bioelectrochemistry (Amsterdam, Netherlands). 2021 Dec:142():107946. doi: 10.1016/j.bioelechem.2021.107946. Epub 2021 Sep 1 [PubMed PMID: 34507162]
Lu Q, Han WJ, Choi HJ. Smart and Functional Conducting Polymers: Application to Electrorheological Fluids. Molecules (Basel, Switzerland). 2018 Nov 2:23(11):. doi: 10.3390/molecules23112854. Epub 2018 Nov 2 [PubMed PMID: 30400169]
Dubal DP, Chodankar NR, Kim DH, Gomez-Romero P. Towards flexible solid-state supercapacitors for smart and wearable electronics. Chemical Society reviews. 2018 Mar 21:47(6):2065-2129. doi: 10.1039/c7cs00505a. Epub 2018 Feb 5 [PubMed PMID: 29399689]
Adams TNG, Jiang AYL, Vyas PD, Flanagan LA. Separation of neural stem cells by whole cell membrane capacitance using dielectrophoresis. Methods (San Diego, Calif.). 2018 Jan 15:133():91-103. doi: 10.1016/j.ymeth.2017.08.016. Epub 2017 Aug 31 [PubMed PMID: 28864355]
Ike IS, Sigalas I, Iyuke S. Understanding performance limitation and suppression of leakage current or self-discharge in electrochemical capacitors: a review. Physical chemistry chemical physics : PCCP. 2016 Jan 14:18(2):661-80. doi: 10.1039/c5cp05459a. Epub 2015 Dec 14 [PubMed PMID: 26659405]
Level 3 (low-level) evidenceKim E, Leverage WT, Liu Y, White IM, Bentley WE, Payne GF. Redox-capacitor to connect electrochemistry to redox-biology. The Analyst. 2014 Jan 7:139(1):32-43. doi: 10.1039/c3an01632c. Epub 2013 Oct 30 [PubMed PMID: 24175311]
Level 3 (low-level) evidenceTsouti V, Boutopoulos C, Zergioti I, Chatzandroulis S. Capacitive microsystems for biological sensing. Biosensors & bioelectronics. 2011 Sep 15:27(1):1-11. doi: 10.1016/j.bios.2011.05.047. Epub 2011 Jun 24 [PubMed PMID: 21752630]
Demir B, Searles DJ. Investigation of the Ionic Liquid Graphene Electric Double Layer in Supercapacitors Using Constant Potential Simulations. Nanomaterials (Basel, Switzerland). 2020 Nov 1:10(11):. doi: 10.3390/nano10112181. Epub 2020 Nov 1 [PubMed PMID: 33139670]
Jesudason CG. Broad considerations concerning electrochemical electrodes in primarily fluid environments. International journal of molecular sciences. 2009 May 18:10(5):2203-2251. doi: 10.3390/ijms10052203. Epub 2009 May 18 [PubMed PMID: 19564949]
Gajewski P, Béguin F. Hydrogel-Polymer Electrolyte for Electrochemical Capacitors with High Volumetric Energy and Life Span. ChemSusChem. 2020 Apr 7:13(7):1876-1881. doi: 10.1002/cssc.201903077. Epub 2020 Mar 5 [PubMed PMID: 31999882]
Gao Y, Zhang H, Song B, Zhao C, Lu Q. Electric Double Layer Based Epidermal Electronics for Healthcare and Human-Machine Interface. Biosensors. 2023 Aug 3:13(8):. doi: 10.3390/bios13080787. Epub 2023 Aug 3 [PubMed PMID: 37622873]
Khairalla B, Brand I. Membrane Potentials Trigger Molecular-Scale Rearrangements in the Outer Membrane of Gram-Negative Bacteria. Langmuir : the ACS journal of surfaces and colloids. 2022 Jan 11:38(1):446-457. doi: 10.1021/acs.langmuir.1c02820. Epub 2021 Dec 28 [PubMed PMID: 34963050]
Wu J. Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics. Chemical reviews. 2022 Jun 22:122(12):10821-10859. doi: 10.1021/acs.chemrev.2c00097. Epub 2022 May 20 [PubMed PMID: 35594506]
Level 3 (low-level) evidenceIrnich W. From defibrillation theory to clinical implications. Pacing and clinical electrophysiology : PACE. 2010 Jul:33(7):814-25. doi: 10.1111/j.1540-8159.2009.02660.x. Epub 2009 Dec 16 [PubMed PMID: 20025700]
Level 3 (low-level) evidenceMiškinis J, Ramonas E, Gurevičienė V, Razumienė J, Dagys M, Ratautas D. Capacitance-Based Biosensor for the Measurement of Total Loss of L-Amino Acids in Human Serum during Hemodialysis. ACS sensors. 2022 Nov 25:7(11):3352-3359. doi: 10.1021/acssensors.2c01342. Epub 2022 Oct 21 [PubMed PMID: 36268654]
Slettengren M, Linnros M, van der Linden J. Silicone Oil Decreases Biofilm Formation in a Capacitance-Based Automatic Urine Measurement System. Sensors (Basel, Switzerland). 2021 Jan 10:21(2):. doi: 10.3390/s21020445. Epub 2021 Jan 10 [PubMed PMID: 33435177]