# Work and electric potentials confused

Living cells actively pump sodium ions inside the cell to outside the cell. Given that the electric potential is 0.070V higher outside the cell than inside the cell and that the cell membran is 0.09E-6 meters thick, how much work must be done to move one sodium ion from inside the cell to outside the cell.

So far I am lost, does voltage have to negative, but then negative work has to be done

## Answers and Replies

Signs are a matter of luck

Apart from that this seems not too difficult. Note that the thickness of the wall makes no difference.

Doc Al
Mentor
Are you positive?

supermenscher said:
So far I am lost, does voltage have to negative, but then negative work has to be done
It requires positive work to move a positive charge from a low to a high potential. (Just like it requires positive work against gravity to lift an object.)

So what's the charge on the sodium ion?

positive 0.070?

Doc Al
Mentor
supermenscher said:
positive 0.070?
A sodium ion is formed by removing an electron. So the charge of the ion is +e = 1.6 E-19 Coulombs.

so is the answer 0.070 * 1.6*10^-19 ?

Doc Al
Mentor
supermenscher said:
so is the answer 0.070 * 1.6*10^-19 ?
Yes. Don't forget to use the proper units: work is measured in Joules.

thank you so much :)

turin
Homework Helper
kuengb said:
Note that the thickness of the wall makes no difference.
I didn't catch that at first ( ). I wonder if it was on purpose.