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In this lesson, we will learn how to calculate the average speed of electron motion in an electric current, known as the drift velocity.

Q1:

A 10-gauge copper wire has a cross-sectional area of 5.26 mm^{2}. The wire carries a current of 5.00 A. One mole of copper contains 6 . 0 2 × 1 0 2 3 atoms has a mass of 63.50 g. What is the magnitude of the drift velocity of the electrons, assuming that each copper atom contributes one free electron to the current? Use a value of 89.5 g/cm^{2} for the density of copper.

Q2:

An aluminum wire and a copper wire, both 2.000 mm in radius, carry currents of 5.00 A. In modeling the flow of charge through these wires, use a value of 8.96 g/cm^{3} for the density of copper, 2.70 g/cm^{3} for the density of aluminum, 26.98 g/mol for the molar mass of aluminum, and 63.5 g/mol for the molar mass of copper. Assume each atom of the metals contributes one free electron to the currents in them.

What is the absolute value of the charge density in the wire?

What is the drift velocity of the electrons?

What would the drift velocity be if the same gauge copper was used instead of aluminum?

Q3:

In a current-carrying copper wire with cross section 𝜎 = 4 . 0 m m 2 , the drift velocity is 0.040 cm/s. Find the total current running through the wire. Use a value of 8 . 4 9 × 1 0 2 8 m^{−3} for the number density of copper.

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