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Electricity and magnetism multiple choice questions

Copper has one conduction electron per atom, that is, each atom contributes one electron that is free to move through the solid. The density of copper is 9 g/cm^3 and its molecular weight is 64 g/mole. A wire carries a current of 10 A. The cross sectioned area of the wire is 3 mm^2.

What is the current density in the wire
What is the number of conduction electrons per m^3
What is the conduction electron drift velocity

In the earth's atmosphere positive charges move toward the earth and negative charges move away from it. The total current is 1800 A. The average value of the electric field responsible for this current near the surface of the earth is 100 N/C. What is electrical resistivity of air at the surface of the earth? The radius of the earth is 6.37 x 10^6 m.

Last question is on a charged particle in a region of electric and magnetic filed.

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Cross sectional area = 3 mm^2 = 3 x 10^-6 m^2
Current density J = I/A = 10/ (3 x 10^-6) A/m^2

J = 3.33 x 106 A/m2

Solution provided does not show the 106 . If you notice, question # 36 uses the value of J in its calculation. ...

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