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## Electric Potential & Capacitance Unit

PROGRESSIVE SCIENCE INITIATIVE® (PSI®)

## Resources

```Dear admin, I have a question about the Homework FRQ Q4 (a). Was the inner shell charged to a potential V before it was put into the outer shell? If the inner shell is being charged with the presence of the grounded outer shell, wouldn&amp;amp;#x27;t the potential of the inner shell be the same as part (c)?

Thank you!```
```Siu Jia,

I don't think it matters.

The potential between the inner shell and the outer shell only depends on the charge on the inner shell. As the potential on the outer shell is the same at all points between radius a and b. And in this case, the potential on the outer shell is equal to zero as it is grounded.

So, the potential at r = a is just equal to kq/a.  The potential at r = b is kq/b. The potential difference is then kq/(1/a - 1/b).

Even if the cell is not grounded, you would get the same potential difference.

John```
```Hi John,
`Jacob, that's fantastic. It's great when our students find our errors. And I appreciate his effort in making our materials better for everyone who uses them. Please pass on my thanks.  John`