# Physics -- Repost

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Homework Help Forum: Physics

Posted by Sandra on Sunday, February 28, 2010 at 10:20am.

Thank you for answering my previous questions!
I have another one now in regards to the following question...

An unknown potential difference exists between the inner and outer surfaces of the membrane of a cell. The inner surface is negative relative to the outer surface. If 1.7 x 10-20 J of work is needed to eject a positive Calcium ion (Ca2+) from the interior of the cell, what is the value of the potential difference?

I think that I should be able to use the formula where work is equal to the charge of the particle times its electric potential difference. The work is given and by using the charge of the calcium ion, the electric potential difference could easily be solved for. However, my question is, what would the charge of the calcium ion be? Do we need to consider it's electrons/protons? Since it's given that it charge is 2+, would I just assume that its 2X the charge of a proton?

* Physics - Sandra, Sunday, February 28, 2010 at 7:18pm

If someone can help, I'd really appreciate it!

• Physics -- Repost -

Yes, that is how to do it. The charge of Ca(2+) is +2e, or 3.2*16^-19 C