# Electric resistance Formula

The electric resistance is the ability of a material to oppose to the flow of charge current in it. The electrical resistance experimentally depends upon how long or short is the material, or its cross sectional area. The resistance of a wire can be expressed as:

Electric resistance = resistivity * length / cross sectional area

The equation is:

R = ρ L/A

Where:

R: Electric Resistance

ρ: Resistivity

L: Length of the material

A: Sectional area of the material

Electric resistance Formula Questions:

1) A wire of copper with sectional area of 3 cm^{2} and length 1 m. What is the resistance?

Answer:

From the electric resistance formula, we substitute the cooper resistivity which is 1.68*10^{(-8)} Ω*m:

R= ρ L /A = 1.68*10^{(-8)} Ω *m * 1 m /0.0003 m^{2}

R = 0.000056 Ω = 56 μ Ω

2) A wire of germanium has a length of 1 m and A= 3 cm^{2}. What is its resistance?

Answer:

From the electric resistance formula, we substitute the germanium resistivity which is 4.6*10^{(-1)} Ω*m:

R= ρ L /A = 4.6*10^{(-1)} Ω *m * 1 m /0.0003 m^{2}

R = 1533.3 Ω = 1.53 kΩ

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