{"id":358,"date":"2025-09-22T12:11:24","date_gmt":"2025-09-22T12:11:24","guid":{"rendered":"https:\/\/probessor.com\/?page_id=358"},"modified":"2026-04-18T18:30:56","modified_gmt":"2026-04-18T18:30:56","slug":"what-is-resistance","status":"publish","type":"page","link":"https:\/\/probessor.com\/index.php\/what-is-resistance\/","title":{"rendered":"What is Resistance"},"content":{"rendered":"\n<div style=\"height:50px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>To start with, it is good to highlight that there are two fundamentally different quantities that are often incorrectly used in parallel and interchangeably:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Resistance<\/strong>\n<ul class=\"wp-block-list\">\n<li>System specific quantity &gt; Longer the path between in\/out, the higher the value<\/li>\n\n\n\n<li>Unit: <strong>Ohm<\/strong> or the greek letter <strong><strong>\u03a9<\/strong><\/strong><\/li>\n\n\n\n<li>Often used for practical purposes<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Resistivity<\/strong>\n<ul class=\"wp-block-list\">\n<li>Material property &gt; calculation includes the dimensions of the measurement system<\/li>\n\n\n\n<li>Unit: <strong>Ohm*m <\/strong>or <strong><strong>\u03a9<\/strong>m<\/strong>, for surface resistivity also <strong>Ohm\/sq<\/strong> or <strong>\u03a9\/\u25a1<\/strong><\/li>\n\n\n\n<li>Used for design calculations, characterization and classification of materials<\/li>\n\n\n\n<li>For non-metallic conductors <strong>Ohm*cm<\/strong> is often preferred due to their relatively high resistances.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<div style=\"height:50px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Resistance of a solid, homogeneous cylinder shape can be calculated as <\/p>\n\n\n\n<p>R = <em>\u03c1<\/em>*L\/A<\/p>\n\n\n\n<p>, where <em>\u03c1<\/em> is the electrical resistivity of the material, L is the length of the shape and A is the cross-sectional area. From the formula it is evident that R doubles if length doubles. The volume resistivity can be expressed as<\/p>\n\n\n\n<p><em>\u03c1<\/em> = R*A\/L<\/p>\n\n\n\n<p>, where R can be replaced with R = U\/I from the Ohm&#8217;s law to the following form<\/p>\n\n\n\n<p><em>\u03c1<\/em> = UA\/IL,<\/p>\n\n\n\n<p>, where U is voltage (V) and I is electric current (A).<\/p>\n\n\n\n<div style=\"height:50px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>This leads to a problemacy. If resistance can be easily measured alongside with voltage, current and dimensions &#8211; why is there a need for so many different probes and measurement fixtures instead of using just the metallic pointy ones that comes with even the cheapest multimeters on the market?<\/p>\n\n\n\n<p>That is due to <strong>contact resistance<\/strong>, an annoyance that is always part of the equation &#8211; and if not not taken into account, can possibly be significant enough to mask the actual resistivity of the material completely. Typical way to take it into account is to carry out the measurements with a more complex 4-point setup.<\/p>\n\n\n\n<p>The measured resistance value measured between a known distance is likely to vary depending on measurement details. Such factors could be the measurement method, tools, ambient conditions (%RH), part production parameters, part\/tool age and state of wear, migration of additives, dust\/staining and the operator influence to name a few variables.<\/p>\n\n\n\n<p>Resistance in its essence expresses how an element in the circuit restricts the flow of electricity &#8211; thus it is evident that the method that gives the lowest value is the most correct, unless the method externally biases the material characteristics. When carrying out a simple 2-point resistance measurement, the value measured is actually three resistance values in series:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>contact resistance between positive electrode and the sample<\/li>\n\n\n\n<li>Intrinsic resistance of the sample<\/li>\n\n\n\n<li>contact resistance between the sample and the negative electrode<\/li>\n<\/ul>\n\n\n\n<p>&#8230; and quite many fail to understand it &#8211; most of the time it requires comparison of multiple methods, not just a single value with a single test system.<\/p>\n\n\n\n<div style=\"height:50px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n","protected":false},"excerpt":{"rendered":"<p>To start with, it is good to highlight that there are two fundamentally different quantities that are often incorrectly used in parallel and interchangeably: Resistance of a solid, homogeneous cylinder shape can be calculated as R = \u03c1*L\/A , where \u03c1 is the electrical resistivity of the material, L is the length of the shape&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-358","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>What is Resistance - Probes and fixtures for material testing<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/probessor.com\/index.php\/what-is-resistance\/\" \/>\n<meta property=\"og:locale\" content=\"fi_FI\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What is Resistance - Probes and fixtures for material testing\" \/>\n<meta property=\"og:description\" content=\"To start with, it is good to highlight that there are two fundamentally different quantities that are often incorrectly used in parallel and interchangeably: Resistance of a solid, homogeneous cylinder shape can be calculated as R = \u03c1*L\/A , where \u03c1 is the electrical resistivity of the material, L is the length of the shape...\" \/>\n<meta property=\"og:url\" content=\"https:\/\/probessor.com\/index.php\/what-is-resistance\/\" \/>\n<meta property=\"og:site_name\" content=\"Probes and fixtures for material testing\" \/>\n<meta property=\"article:modified_time\" content=\"2026-04-18T18:30:56+00:00\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Arvioitu lukuaika\" \/>\n\t<meta name=\"twitter:data1\" content=\"2 minuuttia\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/probessor.com\\\/index.php\\\/what-is-resistance\\\/\",\"url\":\"https:\\\/\\\/probessor.com\\\/index.php\\\/what-is-resistance\\\/\",\"name\":\"What is Resistance - Probes and fixtures for material testing\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/probessor.com\\\/#website\"},\"datePublished\":\"2025-09-22T12:11:24+00:00\",\"dateModified\":\"2026-04-18T18:30:56+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/probessor.com\\\/index.php\\\/what-is-resistance\\\/#breadcrumb\"},\"inLanguage\":\"fi\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/probessor.com\\\/index.php\\\/what-is-resistance\\\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/probessor.com\\\/index.php\\\/what-is-resistance\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/probessor.com\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"What is Resistance\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/probessor.com\\\/#website\",\"url\":\"https:\\\/\\\/probessor.com\\\/\",\"name\":\"Probes and fixtures for material testing\",\"description\":\"Customized tools for measurement of electrical properties of conductive plastics for ESD &amp; 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