find electric field of a spherical shell

unteng10

1. A thin spherical shell of radius 6.8 m has a total charge of 7.77 C distributed uniformly over its surface. Find the electric field E 10.4 m from the center of the shell. Answer in units of N/C.
ke = 8.988 * 10^9 Nm^2/C^2



2. E = ke * (Q/r^2)



3. I did (8.988 * 10^9 Nm^2/C^2)(7.77 C/10.4m^2)
The answer I came up with is 6.4568 * 10^9 N/C, am I doing this correctly?

Delphi51

Yes, looks good to me!

unteng10

I thought so too, but for some reason it keeps telling me my answer is incorrect.

TwoTruths

Do you know the right answer? Are you off by a certain order of magnitude? If yes, you should check to make sure you wrote the units properly. I've forgotten to take into account unit modifiers like micro and nano before. Just a thought, since your work is correct as is.

Doc Al

The formula is fine, you just made an arithmetic error. (Careful with decimal points.)