{"id":8356,"date":"2013-10-29T21:21:36","date_gmt":"2013-10-29T21:21:36","guid":{"rendered":"http:\/\/www.mometrix.com\/academy\/?page_id=8356"},"modified":"2026-03-28T11:16:16","modified_gmt":"2026-03-28T16:16:16","slug":"electric-charge","status":"publish","type":"page","link":"https:\/\/www.mometrix.com\/academy\/electric-charge\/","title":{"rendered":"Electric Charge"},"content":{"rendered":"\n\t\t\t<div id=\"mmDeferVideoEncompass_ycFY9HKQbrc\" style=\"position: relative;\">\n\t\t\t<picture>\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.webp\" type=\"image\/webp\">\n\t\t\t\t<source srcset=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" type=\"image\/jpeg\"> \n\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" loading=\"eager\" id=\"videoThumbnailImage_ycFY9HKQbrc\" data-source-videoID=\"ycFY9HKQbrc\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/circle-play-duotone.png\" alt=\"Electric Charge Video\" height=\"464\" width=\"825\" class=\"size-full\" data-matomo-title = \"Electric Charge\">\n\t\t\t<\/picture>\n\t\t\t<\/div>\n\t\t\t<style>img#videoThumbnailImage_ycFY9HKQbrc:hover {cursor:pointer;} img#videoThumbnailImage_ycFY9HKQbrc {background-size:contain;background-image:url(\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2023\/01\/686-electric-charge-2-2.webp\");}<\/style>\n\t\t\t<script defer>\n\t\t\t  jQuery(\"img#videoThumbnailImage_ycFY9HKQbrc\").click(function() {\n\t\t\t\tlet videoId = jQuery(this).attr(\"data-source-videoID\");\n\t\t\t\tlet helpTag = '<div id=\"mmDeferVideoYTMessage_ycFY9HKQbrc\" style=\"display: none;position: absolute;top: -24px;width: 100%;text-align: center;\"><span style=\"font-style: italic;font-size: small;border-top: 1px solid #fc0;\">Having trouble? <a href=\"https:\/\/www.youtube.com\/watch?v='+videoId+'\" target=\"_blank\">Click here to watch on YouTube.<\/a><\/span><\/div>';\n\t\t\t\tlet tag = document.createElement(\"iframe\");\n\t\t\t\ttag.id = \"yt\" + videoId;\n\t\t\t\ttag.src = \"https:\/\/www.youtube-nocookie.com\/embed\/\" + videoId + \"?autoplay=1&controls=1&wmode=opaque&rel=0&egm=0&iv_load_policy=3&hd=0&enablejsapi=1\";\n\t\t\t\ttag.frameborder = 0;\n\t\t\t\ttag.allow = \"autoplay; fullscreen\";\n\t\t\t\ttag.width = this.width;\n\t\t\t\ttag.height = this.height;\n\t\t\t\ttag.setAttribute(\"data-matomo-title\",\"Electric Charge\");\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_ycFY9HKQbrc\").html(tag);\n\t\t\t\tjQuery(\"div#mmDeferVideoEncompass_ycFY9HKQbrc\").prepend(helpTag);\n\t\t\t\tsetTimeout(function(){jQuery(\"div#mmDeferVideoYTMessage_ycFY9HKQbrc\").css(\"display\", \"block\");}, 2000);\n\t\t\t  });\n\t\t\t  \n\t\t\t<\/script>\n\t\t\n<p><script>\nfunction ToB_Function() {\n  var x = document.getElementById(\"ToB\");\n  if (x.style.display === \"none\") {\n    x.style.display = \"block\";\n  } else {\n    x.style.display = \"none\";\n  }\n}\n<\/script><\/p>\n<div class=\"moc-toc hide-on-desktop hide-on-tablet\">\n<div><button onclick=\"ToB_Function()\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2024\/12\/toc2.svg\" width=\"16\" height=\"16\" alt=\"show or hide table of contents\"><\/button><\/p>\n<p>On this page<\/p>\n<\/div>\n<nav id=\"ToB\" style=\"display:none;\">\n<ul>\n<li class=\"toc-h2\"><a href=\"#Fundamental_Properties\" class=\"smooth-scroll\">Fundamental Properties<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Additivity_and_Net_Charge\" class=\"smooth-scroll\">Additivity and Net Charge<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Electric_Force_and_Interactions\" class=\"smooth-scroll\">Electric Force and Interactions<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Electric_Fields\" class=\"smooth-scroll\">Electric Fields<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Static_Electricity,_Conductors,_and_Insulators\" class=\"smooth-scroll\">Static Electricity, Conductors, and Insulators<\/a><\/li>\n<li class=\"toc-h2\"><a href=\"#Review_Questions\" class=\"smooth-scroll\">Review Questions<\/a><\/li>\n<\/ul>\n<\/nav>\n<\/div>\n<div class=\"accordion\"><input id=\"transcript\" type=\"checkbox\" class=\"spoiler_button\" \/><label for=\"transcript\">Transcript<\/label>\n<div class=\"spoiler\" id=\"transcript-spoiler\">\n<p>Hi, and welcome to this video on electric charge! In this video, we\u2019re going to look at what electric charge is and how it\u2019s measured. Let\u2019s get started!<\/p>\n<h2><span id=\"Fundamental_Properties\" class=\"m-toc-anchor\"><\/span>Fundamental Properties<\/h2>\n<p>\nElectric charge is a fundamental property of <a class=\"ylist\" href=\"https:\/\/www.mometrix.com\/academy\/states-of-matter\/\">matter<\/a>. All physical things in the universe are made up of matter, all matter is made up of <a class=\"ylist\" href=\"https:\/\/www.mometrix.com\/academy\/structure-of-atoms\/\">atoms<\/a>, and atoms are made up of particles. These particles can be positively charged, negatively charged, or neutral. Protons are positively charged, electrons are negatively charged, and neutrons have no charge at all, making them neutral.<\/p>\n<h2><span id=\"Additivity_and_Net_Charge\" class=\"m-toc-anchor\"><\/span>Additivity and Net Charge<\/h2>\n<p>\nOne property of electric charge is that it is additive. This means that when multiple charges of the same kind are put together, they add up to one big charge, be it positive or negative. And if we have a mixture of positive and negative charges, we can find the net charge of the overall mixture.<\/p>\n<p>For example, if we have an object made up of 14 protons, which are positive, and 12 electrons, which are negative, then we end up with a net charge of positive 2. We simply add 1 for each proton and subtract 1 for each electron. If the resulting number is positive, we have a net positive charge and if the resulting number is negative, we\u2019ll have a net negative charge. Note that neutral particles will make no difference in the net charge.<\/p>\n<h2><span id=\"Electric_Force_and_Interactions\" class=\"m-toc-anchor\"><\/span>Electric Force and Interactions<\/h2>\n<p>\nIt\u2019s also important to understand the interaction between charged particles. All electrically charged particles exert a force on all other electrically charged particles, aptly named the electric force. The electric force is described by this equation:<\/p>\n<div class=\"examplesentence\" style=\"font-size: 120%;\"><span style=\"font-size: 90%;\">\\(F =\\)<\/span> \\(\\frac{kq_{1}q_{2}}{d^{2}} \\)<\/div>\n<p>\n&nbsp;<br \/>\nThe letter \\(k\\) is Coulomb\u2019s constant, \\(q_{1}\\) and \\(q_{2}\\) are the two different charges exerting a force on each other, and \\(d\\) is the distance between the centers of the two charges. Note that the sign for each of the charges will impact whether the force between them is attractive or repulsive.<\/p>\n<p>Specifically, if the calculated force is negative (opposite signs on the charges), then the force is attractive. If the calculated force is positive (same signs on the charges), then the force is repulsive.<\/p>\n<p>Note that since distance is in the denominator of the equation, the closer the two charged objects are to each other, the stronger the force is between them.<\/p>\n<h2><span id=\"Electric_Fields\" class=\"m-toc-anchor\"><\/span>Electric Fields<\/h2>\n<p>\nAnother interesting property of electrically charged objects is the electric field surrounding them. We can think of the electric field as lines emanating from the surface of the charged object. For negatively charged objects, we draw the lines with arrows pointing inward to the object and for positively charged objects, we draw the arrows pointing outward. The closer and denser the lines are, the stronger the field is in that spot.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.mometrix.com\/academy\/wp-content\/uploads\/2025\/02\/Electric-field-charges.webp\" alt=\"\" width=\"\" height=\"\" class=\"aligncenter size-full wp-image-215971\"  role=\"img\" style=\"box-shadow: 1.5px 1.5px 3px gray;\"  \/><\/p>\n<p>Theoretically, these lines go on forever, but get weaker the further away they are from the charge. For two like charges, electric field lines will avoid each other and the electric force will push the objects apart.<\/p>\n<p>For opposite charges, the electric field lines will actually connect the two charges and the electric force will draw them closer together. Visually, this is demonstrated by lines that extend all the way from the positive charge to the negative charge, indicating an attraction. All charged particles or objects in an electric field will experience the electric force.<\/p>\n<p>The equation for electric field is:<\/p>\n<div class=\"examplesentence\" style=\"font-size: 120%;\"><span style=\"font-size: 90%;\">\\(E=\\)<\/span> \\(\\frac{kq}{d^{2}}\\)<\/div>\n<p>\n&nbsp;<br \/>\nThe letter \\(k\\) is Coulomb\u2019s constant, \\(q\\) is the charge of the object whose electric field we are measuring, and \\(d\\) is the distance from the charged object whose electric field we are measuring to the spot where we want to determine \\(E\\). The value of the electric field changes depending on where you are.<\/p>\n<p>This is similar to the electric force and it can be pretty easy to mix up the two equations. So, it\u2019s important to remember that the electric <em>force<\/em> describes the interaction between two objects and, therefore, includes a \\(q_{1}\\) and \\(q_{2}\\) and the electric <em>field<\/em> describes the field of one object, so it only has one \\(q\\).<\/p>\n<h2><span id=\"Static_Electricity,_Conductors,_and_Insulators\" class=\"m-toc-anchor\"><\/span>Static Electricity, Conductors, and Insulators<\/h2>\n<p>\nCharge, of course, is not limited to point particles like this. We can have large objects with a net positive or negative charge, as well. Charge that is built up on objects is called static electricity.  Objects handle the build up of charge in a few different ways. The two main categories are conductors and insulators.<\/p>\n<p>Conductors have electrons with the ability to move freely on them and, therefore, have the ability to have a flow of electrical charge through them. Since the electrons can move, the charge will disperse as much as possible for the given shape of the conductor. So, when a conductor, a piece of metal, has attracted extra electrons, it will have a net negative charge dispersed over its surface.<\/p>\n<p>An insulator, on the other hand, does not have the ability to have freely-flowing electrons and cannot have a flow of electrical charge like a conductor. They can still build up a static charge, but it will be localized, since it cannot disperse. Common examples of insulators are glass and wood.<\/p>\n<hr>\n<h2><span id=\"Review_Questions\" class=\"m-toc-anchor\"><\/span>Review Questions<\/h2>\n<p>\nNow that we have an understanding of what electric charge is and how it causes electric forces and fields, let\u2019s think about some examples.<\/p>\n<p>1. What is the net charge of an atom composed of 17 protons, 17 neutrons, and 18 electrons?<\/p>\n<ol style=\"list-style: upper-alpha;\">\n<li>-1<\/li>\n<li>1<\/li>\n<li>0<\/li>\n<li>-18<\/li>\n<\/ol>\n<div style=\"text-align: center; margin-bottom: 20px;\"><button class=\"buttontranscript\" onClick=\"toggle('Answer1')\">Show Answer<\/button><\/div>\n<div id=\"Answer1\" style=\"display:none; box-shadow: 1.5px 1.5px 5px grey; background-color:#E0E0E0; padding: 30px; padding-bottom: 15px; width: 60%; margin: auto; text-align: center;\">\n<strong>The answer is A, -1.<\/strong><\/p>\n<p style=\"text-align: left;\"> The neutrons have no effect on the charge, so \\(-18 + -17 = -1\\).<\/p>\n<\/div>\n<p>\n&nbsp;<br \/>\n2. Imagine a very large metal plate that has a net negative charge. In the middle of the plate, just above it, you place an ionized helium atom containing 2 protons, 2 neutrons, and 1 electron. What will happen to this atom?<\/p>\n<ol style=\"list-style: upper-alpha;\">\n<li>The atom will move directly upward, away from the plate.<\/li>\n<li>The atom will move directly downward, toward the plate.<\/li>\n<li>The atom will remain where it is.<\/li>\n<li>The atom will move to the right.<\/li>\n<\/ol>\n<div style=\"text-align: center; margin-bottom: 20px;\"><button class=\"buttontranscript\" onClick=\"toggle('Answer2')\">Show Answer<\/button><\/div>\n<div id=\"Answer2\" style=\"display:none; box-shadow: 1.5px 1.5px 5px grey; background-color:#E0E0E0; padding: 30px; padding-bottom: 15px; width: 60%; margin: auto; text-align: center;\">\n<strong>The answer is B.<\/strong><\/p>\n<p style=\"text-align: left;\">Since there are more protons than electrons in the ionized helium atom, it has a net positive charge and will be attracted to the negatively charged plate and move downward.<\/p>\n<\/div>\n<p>\n&nbsp;<br \/>\nI hope this review was helpful! 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