{"id":11343,"date":"2024-11-08T17:22:06","date_gmt":"2024-11-08T17:22:06","guid":{"rendered":"https:\/\/fisicaevestibular.com.br\/novo\/?page_id=11343"},"modified":"2024-12-03T13:08:19","modified_gmt":"2024-12-03T13:08:19","slug":"segunda-lei-de-ohm-resistividade-en","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/eletricidade\/eletrodinamica\/segunda-lei-de-ohm-resistividade-en\/","title":{"rendered":"Ohm’s Second Law (Resistivity) – 2024 EN"},"content":{"rendered":"

OHM’S SECOND LAW (RESISTIVITY)<\/span><\/h1>\n
\n

Ohm’s Second Law (Resistivity)<\/span><\/b><\/p>\n

 <\/p>\n

Through\u00a0<\/span><\/b>research,\u00a0<\/span><\/b>Ohm discovered that the electrical resistance of a conductor\u00a0<\/b>, kept at a\u00a0<\/b>constant temperature, depends on three factors:<\/b><\/span><\/b><\/b><\/b><\/b><\/p>\n

\"\"\u00a0The\u00a0<\/span><\/b>electrical resistance R is directly proportional to the length L of the wire.<\/span><\/b><\/p>\n

Consider a\u00a0<\/span><\/b>conductive metal wire of the same material (\u00a0<\/span><\/b>for example ,\u00a0<\/span><\/b>copper\u00a0<\/b><\/span>Cu) and the same cross-sectional area\u00a0\u00a0<\/span><\/b>S\u00a0<\/span><\/b>, subjected to a constant potential difference\u00a0\u00a0<\/span><\/b>U.<\/span><\/b><\/b><\/p>\n

\"\"<\/p>\n

Experimentally\u00a0<\/span><\/b>it is found that R is directly proportional to L,\u00a0<\/span><\/b>that is, a\u00a0<\/span><\/b>double length corresponds to a double resistance, a triple length, triple resistance, etc.<\/span><\/b><\/p>\n

\"\"\u00a0The\u00a0<\/span><\/b>electrical resistance R is inversely proportional to the cross-sectional area (S).<\/span><\/b><\/p>\n

In the diagram below, the\u00a0<\/span><\/b>wires are of the same material and the same length L,\u00a0<\/span><\/b>but with\u00a0<\/span><\/b>straight sections (thicknesses) of different areas S.<\/span><\/b><\/p>\n

\"\"<\/p>\n

In this case, the\u00a0<\/span><\/b>resistance R is inversely proportional to S,\u00a0<\/span><\/b>that is, at a\u00a0<\/span><\/b>double cross-sectional area, the resistance drops by half; at a triple area, resistance three times less, etc.<\/span><\/b><\/p>\n

\"\"\u00a0The\u00a0<\/span><\/b>electrical resistance R depends on the material that makes up the body.<\/span><\/b><\/p>\n

Wires of the same length L and the same cross-sectional area S, but made of different materials, have different electrical resistances.<\/span><\/b><\/p>\n

\"\"<\/p>\n

This\u00a0<\/span><\/b>dependence of the resistance value on the material that makes up the resistor is called\u00a0<\/span><\/b>\u00a0the resistivity\u00a0\u00a0<\/span><\/b>of the material and is represented by the Greek letter \u03c1 \u201cr\u00f4\u201d.<\/span><\/b><\/p>\n

 <\/p>\n

<\/b>The\u00a0<\/b>three factors\u00a0<\/b>above\u00a0<\/b>can be\u00a0<\/b><\/span>mathematically represented by\u00a0<\/span><\/b>the equation:<\/b><\/span><\/b><\/b><\/b><\/b><\/p>\n

\"\"<\/p>\n

Derivation of the unit of resistivity (\u03c1) in the international system of units (SI)\u00a0<\/span><\/b><\/b><\/p>\n

\"\"<\/p>\n

What you should know, information and tips<\/span><\/p>\n

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\"\"<\/p>\n

When you state that the\u00a0<\/span><\/b>SI resistivity of aluminum is \u03c1\u00a0<\/span><\/b>Al<\/span><\/b><\/sub>\u00a0= 2.8.108\u00a0<\/span><\/b>\u03a9m<\/span><\/b><\/sup>\u00a0, you mean that an\u00a0<\/b>aluminum conductor, 1 m long and 1\u00a0<\/b>m2<\/b><\/sup>\u00a0\u00a0in cross-sectional area\u00a0<\/b>, has a\u00a0<\/b>resistance of R = 2.8.108\u00a0<\/b><\/span>\u03a9\u00a0<\/span><\/b>,<\/b><\/sup>\u00a0maintained at a constant temperature, in our example at 20\u00a0<\/b>o<\/b><\/sup>\u00a0C.<\/b><\/span><\/b><\/b><\/b><\/b><\/b><\/b><\/b><\/b><\/b><\/b><\/p>\n

\"\"<\/p>\n

Table with resistivity values \u200b\u200bof some materials<\/span><\/b><\/p>\n

\"\"<\/p>\n

\"\"\u00a0Rheostats<\/span><\/b><\/p>\n

Rheostats\u00a0<\/span><\/b>are variable resistors\u00a0<\/span><\/b>whose purpose is\u00a0<\/span><\/b>to adapt the intensity of the electric current to desired values.<\/span><\/b><\/p>\n

Types of rheostats:<\/span><\/b><\/p>\n

The\u00a0<\/span><\/b>main types of rheostats are\u00a0<\/span><\/b>cursor rheostat\u00a0<\/b>varying the cursor\u00a0<\/b>you are<\/b><\/span>\u00a0\u00a0\"\"\u00a0\u00a0<\/b><\/b>\u00a0\"\"<\/b><\/b><\/b><\/p>\n

\"\"varying the resistance\u00a0<\/span><\/b>(figure 1) \u00a0\u00a0<\/span>\"\"\u00a0\u00a0<\/b>point\u00a0\u00a0<\/b><\/span>rheostat\u00a0<\/span><\/b>in\u00a0<\/b>each position of the switch\u00a0<\/b>the\u00a0<\/b>electrical resistance\u00a0<\/b>has\u00a0<\/b>a\u00a0<\/b>certain value\u00a0<\/b>(figure 2).<\/b><\/span><\/b><\/b>\u00a0\"\"<\/b><\/b><\/b><\/b><\/b><\/b><\/b><\/p>\n

Check out the exercises with commented solutions<\/span><\/a><\/h3>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

OHM’S SECOND LAW (RESISTIVITY) Ohm’s Second Law (Resistivity)   Through\u00a0research,\u00a0Ohm discovered that the electrical resistance of a conductor\u00a0, kept at a\u00a0constant temperature, depends on three factors: \u00a0The\u00a0electrical resistance R is directly proportional to the length L of the wire. Consider a\u00a0conductive metal wire of the same material (\u00a0for example ,\u00a0copper\u00a0Cu) and the same cross-sectional area\u00a0\u00a0S\u00a0, subjected to a constant potential<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1676,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-11343","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/11343","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/comments?post=11343"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/11343\/revisions"}],"predecessor-version":[{"id":12018,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/11343\/revisions\/12018"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/1676"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=11343"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}