Electric Current Ohms Law Resistivity It is found

Resistivity • It is found experimentally that the resistance R of an electrical conductor

• Note that good conductor of electricity have a low resistivity and good

• The conductivity σ • The reciprocal of the resistivity , called the

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Electric Current : •

• Ohm's Law

Resistivity • It is found experimentally that the resistance R of an electrical conductor depends on 4 factors, these being • (1) - length of the conductor. • resistance R is directly proportional to length. R α l • (2) the cross –sectional area of the conductor. • resistance R is inversely proportional to its cross –sectional area A of the conductor. R α 1 / A • ( 3) the type of material • ( 4) the temperature of the material

• Note that good conductor of electricity have a low resistivity and good insulator have a high value of resistivity

• The conductivity σ • The reciprocal of the resistivity , called the conductivity σ • σ=1/p • has units of (Ω. m ) -1 • Notice that the resistance of a conductor depends on the geometry of the conductor, and the resistivity of the conductor depends only on the electronic structure of the material. • Example 8: A 0. 90 V potential difference is maintained across a 1. 5 m length of tungsten wire that has a cross-sectional area of 0. 60 mm 2. What is the current in the wire?