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In the time between posting this and now, I have found my mistake. So, problem solved.

Earth's lower atmosphere contains negative and positive ions, created by radioactive elements in the soil and cosmic rays from space. In a certain region, the atmospheric electric field strength is 140 V/m and the field is directed vertically down. This field causes singly charged positive ions, at a density of 610 cm^-3, to drift downward and singly charged negative ions, at a density of 550 cm^-3, to drift upward. The measured conductivity of the air in that region is 2.70 multiplied by 10-14 (ohm·m)^-1.

Calculate the magnitude of the current density.

J = conductivity * E

J = nev

(v here represents the drift speed)

I was writing this and lost what I wrote (alas, I was too verbose!), so here's it quick:

J = conductivity * E = 2.7*10^-14 * 140 = 3.78*10^-12 <<------- correct

v = J / ne

Here we have two values for n, one of positive ions and one of negative ions. So I figured I could write:

v = J / (e(n1-n2))

where n1 represents the density of the positive ions and n2 of the negative.

I checked my math a whole lot, but I keep coming out with v = 0.393258427 m/s, which is wrong, says www.webassign.com.

So apparently I can't just take the net drift?

**1. Homework Statement**Earth's lower atmosphere contains negative and positive ions, created by radioactive elements in the soil and cosmic rays from space. In a certain region, the atmospheric electric field strength is 140 V/m and the field is directed vertically down. This field causes singly charged positive ions, at a density of 610 cm^-3, to drift downward and singly charged negative ions, at a density of 550 cm^-3, to drift upward. The measured conductivity of the air in that region is 2.70 multiplied by 10-14 (ohm·m)^-1.

Calculate the magnitude of the current density.

**2. Homework Equations**J = conductivity * E

J = nev

(v here represents the drift speed)

**3. The Attempt at a Solution**I was writing this and lost what I wrote (alas, I was too verbose!), so here's it quick:

J = conductivity * E = 2.7*10^-14 * 140 = 3.78*10^-12 <<------- correct

v = J / ne

Here we have two values for n, one of positive ions and one of negative ions. So I figured I could write:

v = J / (e(n1-n2))

where n1 represents the density of the positive ions and n2 of the negative.

I checked my math a whole lot, but I keep coming out with v = 0.393258427 m/s, which is wrong, says www.webassign.com.

So apparently I can't just take the net drift?

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