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<title>Electroscope</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Electroscope</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">For the 19th century conceptual model of television, see <a href="Telectroscope" title="Telectroscope">Telectroscope</a>.</div>

<p>The <b>electroscope</b> is an early <a href="Scientific_instrument" title="Scientific instrument">scientific instrument</a> used to detect the presence of <a href="Electric_charge" title="Electric charge">electric charge</a> on a body. It detects this by the movement of a test charge due to the <a href="Coulomb's_law" title="Coulomb's law">Coulomb electrostatic force</a> on it. The amount of charge on an object is proportional to its <a href="Voltage" title="Voltage">voltage</a>. The accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are used with high voltage sources such as <a href="Static_electricity" title="Static electricity">static electricity</a> and <a href="Electrostatic_machine" class="mw-redirect" title="Electrostatic machine">electrostatic machines</a>. An electroscope can only give a rough indication of the quantity of charge; an instrument that measures electric charge quantitatively is called an <i><a href="Electrometer" title="Electrometer">electrometer</a></i>.

</p><p>The electroscope was the first electrical <a href="Measuring_instrument" class="mw-redirect" title="Measuring instrument">measuring instrument</a>. The first electroscope was a pivoted needle (called the <i><a href="Versorium" title="Versorium">versorium</a></i>), invented by British physician <a href="William_Gilbert_(astronomer)" class="mw-redirect" title="William Gilbert (astronomer)">William Gilbert</a> around 1600.<sup id="cite_ref-Gilbert_1-0" class="reference"><a href="#cite_note-Gilbert-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-EB1911_2-0" class="reference"><a href="#cite_note-EB1911-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> The <b>pith-ball electroscope</b> and the <b>gold-leaf electroscope</b> are two classical types of electroscope<sup id="cite_ref-EB1911_2-1" class="reference"><a href="#cite_note-EB1911-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> that are still used in physics education to demonstrate the principles of <a href="Electrostatics" title="Electrostatics">electrostatics</a>. A type of electroscope is also used in the <a href="Quartz_fiber_radiation_dosimeter" class="mw-redirect" title="Quartz fiber radiation dosimeter">quartz fiber radiation dosimeter</a>. Electroscopes were used by the Austrian scientist

<a href="Victor_Hess" title="Victor Hess">Victor Hess</a> in the discovery of <a href="Cosmic_rays" class="mw-redirect" title="Cosmic rays">cosmic rays</a>.

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<div class="mw-heading mw-heading2"><h2 id="Pith-ball_electroscope">Pith-ball electroscope</h2></div>

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</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:204px;max-width:204px"><div class="trow"><div class="tsingle" style="width:202px;max-width:202px"><div class="thumbimage"><span typeof="mw:File"></span></div><div class="thumbcaption">Pith ball electroscope from the 1870s, showing attraction to charged object</div></div></div><div class="trow"><div class="tsingle" style="width:202px;max-width:202px"><div class="thumbimage"><span typeof="mw:File"></span></div><div class="thumbcaption">How it works</div></div></div></div></div>

<p>In 1731, <a href="Stephen_Gray_(scientist)" title="Stephen Gray (scientist)">Stephen Gray</a> used a simple hanging thread, which would be attracted to any nearby charged object. This was the first improvement on Gilbert's <a href="Versorium" title="Versorium">versorium</a> from 1600.<sup id="cite_ref-Baigrie33_3-0" class="reference"><a href="#cite_note-Baigrie33-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

</p><p>The pith-ball electroscope, invented by British schoolmaster and physicist <a href="John_Canton" title="John Canton">John Canton</a> in 1754, consists of one or two small balls of a lightweight nonconductive substance, originally a spongy plant material called <a href="Pith" title="Pith">pith</a>,<sup id="cite_ref-Derry_4-0" class="reference"><a href="#cite_note-Derry-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> suspended by <a href="Silk" title="Silk">silk</a> or linen thread from the hook of an <a href="Electrical_insulation" class="mw-redirect" title="Electrical insulation">insulated</a> stand.<sup id="cite_ref-elliott_5-0" class="reference"><a href="#cite_note-elliott-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> <a href="Tiberius_Cavallo" title="Tiberius Cavallo">Tiberius Cavallo</a> made an electroscope in 1770 with pith balls at the end of silver wires.<sup id="cite_ref-Baigrie33_3-1" class="reference"><a href="#cite_note-Baigrie33-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Modern electroscopes usually use balls made of plastic. In order to test the presence of a charge on an object, the object is brought near to the uncharged pith ball. If the object is charged, the ball will be attracted to it and move toward it.

</p><p>The attraction occurs because of induced <a href="Dipole" title="Dipole">polarization</a><sup id="cite_ref-Sherwood_6-0" class="reference"><a href="#cite_note-Sherwood-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> of the <a href="Atom" title="Atom">atoms</a> inside the pith ball.<sup id="cite_ref-Kaplan_7-0" class="reference"><a href="#cite_note-Kaplan-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Tippens_8-0" class="reference"><a href="#cite_note-Tippens-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Henderson_9-0" class="reference"><a href="#cite_note-Henderson-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Winn_10-0" class="reference"><a href="#cite_note-Winn-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> All matter consists of electrically charged particles located close together; each atom consists of a positively charged <a href="Atomic_nuclei" class="mw-redirect" title="Atomic nuclei">nucleus</a> with a cloud of negatively charged <a href="Electron" title="Electron">electrons</a> surrounding it. The pith is an <a href="Insulator_(electricity)" title="Insulator (electricity)">insulator</a>, so the <a href="Electron" title="Electron">electrons</a> in the ball are bound to atoms of the pith and are not free to leave the atoms and move about in the ball, but they can move a little within the atoms. See diagram. If, for example, a positively charged object <i>(B)</i> is brought near the pith ball <i>(A)</i>, the negative <a href="Electron" title="Electron">electrons</a> <i><span style="color:blue;">(blue minus signs)</span></i> in each atom <i><span style="background-color:yellow; color:;">(yellow ovals)</span></i> will be attracted and move slightly toward the side of the atom nearer the object. The positively charged <a href="Atomic_nucleus" title="Atomic nucleus">nuclei</a> <i><span style="color:red;">(red plus signs)</span></i> will be repelled and will move slightly away. Since the negative charges in the pith ball are now nearer to the object than the positive charges <i>(C)</i>, their attraction is greater than the repulsion of the positive charges, resulting in a net attractive force.<sup id="cite_ref-Kaplan_7-1" class="reference"><a href="#cite_note-Kaplan-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> This separation of charge is microscopic, but since there are so many atoms, the tiny forces add up to a large enough force to move a light pith ball.

</p><p>If the external object <i>(B)</i> instead has a negative charge, the positive nuclei of each atom will be attracted toward it while the electrons will be repelled away from it. Again, this causes opposite charges to be closer to the external object than charges of the same polarity, resulting in a net attractive force.

</p><p>The pith ball can be charged by touching it to a charged object, so some of the charges on the surface of the charged object move to the surface of the ball. Then the ball can be used to distinguish the polarity of charge on other objects because it will be repelled by objects charged with the same polarity or sign it has, but attracted to charges of the opposite polarity.

</p><p>Often the electroscope will have a pair of suspended pith balls. This allows one to tell at a glance whether the pith balls are charged. If one of the pith balls is touched to a charged object, charging it, the second one will be attracted and touch it, communicating some of the charge to the surface of the second ball. Now both balls have the same polarity charge, so they repel each other. They hang in an inverted 'V' shape with the balls spread apart. The distance between the balls will give a rough idea of the magnitude of the charge.

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<div class="mw-heading mw-heading2"><h2 id="Gold-leaf_electroscope">Gold-leaf electroscope</h2></div>

<p>The <a href="Gold-leaf" class="mw-redirect" title="Gold-leaf">gold-leaf</a> electroscope was developed in 1787 by British clergyman and physicist <a href="Abraham_Bennet" title="Abraham Bennet">Abraham Bennet</a>,<sup id="cite_ref-Derry_4-1" class="reference"><a href="#cite_note-Derry-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> as a more sensitive instrument than pith ball or <a href="Straw" title="Straw">straw</a> blade electroscopes then in use.<sup id="cite_ref-eb_11-0" class="reference"><a href="#cite_note-eb-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> It consists of a vertical <a href="Metal" title="Metal">metal</a> rod, usually <a href="Brass" title="Brass">brass</a>, from the end of which hang two parallel strips of thin flexible <a href="Gold_leaf" title="Gold leaf">gold leaf</a>. A disk or ball terminal is attached to the top of the rod, where the charge to be tested is applied.<sup id="cite_ref-eb_11-1" class="reference"><a href="#cite_note-eb-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> To protect the gold leaves from drafts of air they are enclosed in a glass bottle, usually open at the bottom and mounted over a <a href="Electrical_conductor" title="Electrical conductor">conductive</a> base. Often there are <a href="Ground_(electricity)" title="Ground (electricity)">grounded</a> metal plates or foil strips in the bottle flanking the gold leaves on either side. These are a safety measure; if an excessive charge is applied to the delicate gold leaves, they will touch the grounding plates and discharge before tearing. They also capture charge leaking through the air that accumulates on the glass walls, increasing the sensitivity of the instrument. In the precision instruments the inside of the bottle was occasionally evacuated, to prevent the charge on the terminal from leaking off through the ionization of the air.

</p><p>When the metal terminal is touched with a charged object, the gold leaves spread apart in an inverted 'V'. This is because some of the charge from the object is conducted through the terminal and metal rod to the leaves.<sup id="cite_ref-eb_11-2" class="reference"><a href="#cite_note-eb-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> Since the leaves receive the same sign charge they repel each other and thus diverge. If the terminal is <a href="Electrical_ground" class="mw-redirect" title="Electrical ground">grounded</a> by touching it with a <a href="Finger" title="Finger">finger</a>, the charge is transferred through the <a href="Human_body" title="Human body">human body</a> into the earth and the gold leaves close together.

</p><p>The electroscope leaves can also be charged without touching a charged object to the terminal, by <a href="Electrostatic_induction" title="Electrostatic induction">electrostatic induction</a>. As the charged object is brought near the electroscope terminal, the leaves spread apart, because the <a href="Electric_field" title="Electric field">electric field</a> from the object induces a charge in the conductive electroscope rod and leaves, and the charged leaves repel each other. The opposite-sign charge is attracted to the nearby object and collects on the terminal disk, while the same-sign charge is repelled from the object and collects on the leaves (but only as much as left the terminal), so the leaves repel each other. If the electroscope is grounded while the charged object is nearby, by touching it momentarily with a finger, the repelled same-sign charges travel through the contact to ground, leaving the electroscope with a net charge having the opposite sign as the object. The leaves initially hang down free because the net charge is concentrated at the terminal end. When the charged object is moved away, the charge at the terminal spreads into the leaves, causing them to spread apart again.

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<li class="gallerycaption">Gold-leaf electroscopes</li>

<div class="gallerytextwrapper" style="width: 90px"><div class="gallerytext">Condensing electroscope, Rome University physics dept.</div>

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<div class="gallerytextwrapper" style="width: 110px"><div class="gallerytext">Electroscope from about 1910 with grounding electrodes inside jar, as described above</div>

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<div class="gallerytextwrapper" style="width: 107px"><div class="gallerytext">Homemade electroscope, 1900</div>

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<ul><li><a href="Electrical_measurements" title="Electrical measurements">Electrical measurements</a></li>

<li><a href="Electrostatic_fieldmeter" title="Electrostatic fieldmeter">Electrostatic fieldmeter</a></li>

<li><a href="Faraday_cup_electrometer" title="Faraday cup electrometer">Faraday cup electrometer</a></li>

<li><a href="Radiation" title="Radiation">Radiation</a></li></ul>

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<div class="mw-heading mw-heading2"><h2 id="Footnotes">Footnotes</h2></div>

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.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("./mw/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("./mw/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("./mw/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("./mw/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}

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</style><cite id="CITEREFGilbertEdward_Wright1893" class="citation book cs1">Gilbert, William; Edward Wright (1893). <a rel="nofollow" class="external text" href="https://archive.org/details/williamgilbertc00wriggoog"><i>On the Lodestone and Magnetic Bodies</i></a>. John Wiley & Sons. p. <a rel="nofollow" class="external text" href="https://archive.org/details/williamgilbertc00wriggoog/page/n148">79</a>.</cite> a translation by P. Fleury Mottelay of William Gilbert (1600) <i>Die Magnete</i>, London</span>

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<li id="cite_note-EB1911-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-EB1911_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-EB1911_2-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><cite id="CITEREFFleming1911" class="citation encyclopaedia cs1">Fleming, John Ambrose (1911). <span class="cs1-ws-icon" title="s:1911 Encyclopædia Britannica/Electroscope"><a class="external text external" href="https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Electroscope">"Electroscope" </a></span>. In <a href="Hugh_Chisholm" title="Hugh Chisholm">Chisholm, Hugh</a> (ed.). <i><a href="Encyclop%C3%A6dia_Britannica_Eleventh_Edition" title="Encyclopædia Britannica Eleventh Edition">Encyclopædia Britannica</a></i>. Vol. 9 (11th ed.). Cambridge University Press. p. 239.</cite></span>

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<li id="cite_note-Baigrie33-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-Baigrie33_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Baigrie33_3-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><cite id="CITEREFBaigrie2007" class="citation book cs1">Baigrie, Brian (2007). <i>Electricity and magnetism: A historical perspective</i>. Westport, CT: Greenwood Press. p. 33.</cite></span>

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<li id="cite_note-Derry-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-Derry_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Derry_4-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><cite id="CITEREFDerryWilliams,_Trevor1993" class="citation book cs1">Derry, Thomas K.; Williams, Trevor (1993) [1961]. <a rel="nofollow" class="external text" href="https://books.google.com/books?id=mf88HKKYEbQC&pg=PA609"><i>A Short History of Technology: from Earliest Times to A.D. 1900</i></a>. Dover. p. 609. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-486-27472-1</bdi>.</cite> p. 609</span>

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<li id="cite_note-elliott-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-elliott_5-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFElliott1999" class="citation journal cs1">Elliott, P. (1999). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200327140258/http://www.journals.royalsoc.ac.uk/content/klgdd0umcmvjqnpr/fulltext.pdf">"Abraham Bennet F.R.S. (1749–1799): a provincial electrician in eighteenth-century England"</a> <span class="cs1-format">(PDF)</span>. <i>Notes and Records of the Royal Society of London</i>. <b>53</b> (1): 61. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1098%2Frsnr.1999.0063">10.1098/rsnr.1999.0063</a>. <a href="JSTOR_(identifier)" class="mw-redirect" title="JSTOR (identifier)">JSTOR</a> <a rel="nofollow" class="external text" href="https://www.jstor.org/stable/531928">531928</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:144062032">144062032</a>. Archived from <span class="id-lock-subscription" title="Paid subscription required"><a rel="nofollow" class="external text" href="http://www.journals.royalsoc.ac.uk/content/klgdd0umcmvjqnpr/fulltext.pdf">the original</a></span> <span class="cs1-format">(PDF)</span> on 2020-03-27<span class="reference-accessdate">. Retrieved <span class="nowrap">2007-09-02</span></span>.</cite></span>

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<li id="cite_note-Sherwood-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-Sherwood_6-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFSherwoodRuth_W._Chabay2011" class="citation book cs1">Sherwood, Bruce A.; <a href="Ruth_Chabay" title="Ruth Chabay">Ruth W. Chabay</a> (2011). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=8oyNPd5QbYgC&q=polarization+induced+insulator+attract&pg=PA595"><i>Matter and Interactions</i></a> (3rd ed.). US: John Wiley and Sons. pp. <span class="nowrap">594–</span>596. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-470-50347-8</bdi>.</cite></span>

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<li id="cite_note-Kaplan-7"><span class="mw-cite-backlink">^ <a href="#cite_ref-Kaplan_7-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Kaplan_7-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><cite class="citation book cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20140131021101/http://books.google.com/books?id=pPleL5NOtb4C&pg=PA329&dq=%22pith+ball+electroscope%22+induction&hl=en&sa=X&ei=UOL_Tr-0GeeRiQK76aTCCg&ved=0CEcQ6AEwAQ#v=onepage&q=%22pith%20ball%20electroscope%22%20induction&f=false"><i>Kaplan MCAT Physics 2010–2011</i></a>. USA: Kaplan Publishing. 2009. p. 329. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4277-9875-6</bdi>. Archived from <a rel="nofollow" class="external text" href="https://books.google.com/books?id=pPleL5NOtb4C&q=%22pith+ball+electroscope%22+induction&pg=PA329">the original</a> on 2014-01-31.</cite></span>

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<li id="cite_note-Tippens-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-Tippens_8-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.docstoc.com/docs/76893329/Electric-Force">Paul E. Tippens, <i>Electric Charge and Electric Force</i>, Powerpoint presentation, pp. 27–28, 2009, S. Polytechnic State Univ.</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120419225338/http://www.docstoc.com/docs/76893329/Electric-Force">Archived</a> April 19, 2012, at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a> on DocStoc.com website</span>

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<li id="cite_note-Henderson-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-Henderson_9-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFHenderson2011" class="citation web cs1">Henderson, Tom (2011). <a rel="nofollow" class="external text" href="http://www.physicsclassroom.com/class/estatics/u8l1e.cfm">"Charge and Charge Interactions"</a>. <i>Static Electricity, Lesson 1</i>. The Physics Classroom<span class="reference-accessdate">. Retrieved <span class="nowrap">2012-01-01</span></span>.</cite></span>

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<li id="cite_note-Winn-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-Winn_10-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFWinn2010" class="citation book cs1">Winn, Will Winn (2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=WRuRvz_ZD1AC&q=dielectric+polarization"><i>Introduction to Understandable Physics Vol. 3: Electricity, Magnetism and Light</i></a>. US: Author House. p. 20.4. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4520-1590-3</bdi>.</cite></span>

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<li id="cite_note-eb-11"><span class="mw-cite-backlink">^ <a href="#cite_ref-eb_11-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-eb_11-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-eb_11-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text">*[Anon.] (2001) "Electroscope", <i><a href="Encyclopaedia_Britannica" class="mw-redirect" title="Encyclopaedia Britannica">Encyclopaedia Britannica</a></i></span>

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<li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><cite id="CITEREFphi6guy2025" class="citation audio-visual cs1">phi6guy (2025-07-03). <a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=aqbF58cFhCQ"><i>Coulomb's law | Electrostatics | Electric Charges and Fields | NCERT Class 12 Physics |</i></a><span class="reference-accessdate">. Retrieved <span class="nowrap">2025-07-04</span></span> – via YouTube.</cite><span class="cs1-maint citation-comment"><code class="cs1-code">{{cite AV media}}</code>: CS1 maint: numeric names: authors list (link)</span></span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://demos.smu.ca/index.php/demos/e-n-m/52-pith-balls">"Pith-ball electroscope"</a>. <i>Physics demonstration resource</i>. St. Mary's University<span class="reference-accessdate">. Retrieved <span class="nowrap">2015-05-28</span></span>.</cite></li>

<li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20220703000434/http://mw.concord.org/modeler1.3/mirror/electrostatics/electroscope.html">"Computer simulation of electroscopes"</a>. <i>Molecular Workbench</i>. Concord Consortium. Archived from <a rel="nofollow" class="external text" href="http://mw.concord.org/modeler1.3/mirror/electrostatics/electroscope.html">the original</a> on 2022-07-03<span class="reference-accessdate">. Retrieved <span class="nowrap">2008-02-03</span></span>.</cite></li>

<li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=aeiqw81kGio">"Pith Ball and Charged Rod Video"</a>. <i>St. Mary's Physics YouTube Channel</i>. St. Mary's Physics Online. <a rel="nofollow" class="external text" href="https://ghostarchive.org/varchive/youtube/20211222/aeiqw81kGio">Archived</a> from the original on 2021-12-22.</cite></li></ul></div><div><div class="zim-footer">

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