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I got 1.708x10^-55

Hi dennis.colon.jr, thanks for the comment. I can't see where the mistake is to arrive at the $1.7 \times 10^{-55}$ figure, but I've doubled checked that the answer I've provided is correct. If you have a more specific question about the solution, just let me know.

All the best,
Mr. Dychko

How are you supposed to know that the comb gained (rather than lost) electrons? I know that the chapter mentions that plastic items develop negative charges when rubbed, but I thought the problem would specify that the charge acquired was -3 microcoulombs if the comb had gained (vs. lost) electrons?
Thanks,
Julia

Hi julia.wolfe,

I think the question would be worded better if it said $-3.0 \textrm{ } \mu \textrm{C}$. I don't think you're meant to know that plastic gains electrons, although in this case, without the question specifying a negative charge, knowing the properties of plastic is the only way to know. I would presume that in any real test question that the negative sign would be given.

All the best,
Mr. Dychko