Giancoli 7th Edition textbook cover
Giancoli's Physics: Principles with Applications, 7th Edition
18
Electric Currents
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18-2 and 18-3: Electric Current, Resistance, Ohm's Law
18-4: Resistivity
18-5 and 18-6: Electric Power
18-7: Alternating Current
18-8: Microscopic View of Electric Current
18-10: Nerve Conduction

Question by Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014, Reprinted by permission of Pearson Education Inc., New York.
Problem 3
Q

What is the current in amperes if 1200 Na+1200 \textrm{ Na}^+ flow across a cell membrane in 3.1  μs3.1 \; \mu \textrm{s}? The charge on the sodium is the same as on an electron, but positive.

A
6.2×1011 A6.2 \times 10^{-11} \textrm{ A}
Giancoli 7th Edition, Chapter 18, Problem 3 solution video poster
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VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. We have to do some unit conversion here and also recognize that each sodium ion has a charge of one-plus. So each sodium ion is a charge of one electron. And so we multiply that by 1.6 times 10 to the minus 19 Coulombs per electron, and we're told there's 1200 sodium ions have passed in 3.1 microseconds. So we have 1200 times this conversion factor here. This is per 3.1 microseconds. And we have to always get our units into meters-kilograms-seconds, and so it's MKS units. So seconds here is what we need. So multiply it by 1 microsecond for every 10 to minus 6 seconds. The microseconds cancel. And we're left with 6.2 times 10 to the minus 11 amps is the current.

COMMENTS
By daniel.weiss1 on Fri, 9/30/2016 - 6:02 PM

Great video, small note: I think you mistakenly have coulombs in your answer above the video instead of amps.

By Mr. Dychko on Sun, 10/9/2016 - 8:01 PM

Thanks daniel.weiss1! I just fixed it.

All the best,
Mr. Dychko

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