Aim: How do we explain resistance?

Do Now: 1. What is the difference between conventional current and electron current? Conventional Current is the flow of positive charges while Electron Current is the flow of negative charges. 2. What condition is necessary for a current to be established? Potential Difference

Sources of Potential Difference or Voltage

Galvanic Cell

Electric Circuit A path for current to flow.

Typical Path of an Electron

Three Concepts Potential Difference Current Resistance What is resistance? An opposition to current

What are the four factors that the resistance of a material depends on?

Factors that affect Resistance Length Cross Sectional Area Resistivity Temperature

Resistance Problems R=ρL/A=(150 x 10-8 Ω m)(1m)/(0.1 m2 ) R=0.000015 Ω Two wires - A and B - with circular cross-sections have identical lengths and are made of the same material. Yet, wire A has four times the resistance of wire B. How many times greater is the cross sectional area of wire B than wire A? Wire B must have 4 times the cross sectional area of wire A 2. Calculate the resistance of a 1 m long nichrome wire with a cross sectional area of 0.1 m^2. R=ρL/A=(150 x 10-8 Ω m)(1m)/(0.1 m2 ) R=0.000015 Ω

Resistance Problems 3. A 6.50 meter long copper wire at 20 degrees Celsius has a cross-sectional area of 3 mm2. What is the resistance of the wire? R=ρL/A ρ=1.72 x 10-8 Ω m L=6.5 m A= 3 mm2 (10-3 m/mm)(10-3 m/mm)=3 x 10-6 m2 R=0.037 Ω

Resistance Problems A metal conductor is used in an electric circuit. The electrical resistance provided by the conductor could be increased by Decreasing the length of the conductor Decreasing the applied voltage in the circuit Increasing the temperature of the conductor Increasing the cross-sectional area of the conductor