Physics Help Forum Charge Problem

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 Feb 6th 2018, 07:59 AM #1 Junior Member     Join Date: Nov 2017 Location: The Jurassic Forests Posts: 14 Charge Problem I had the problem: An iron arrowhead has an initial charge of 3.35e−6 C. How many electrons are required to give it a charge of −2.82 μC? This was my attempt- 1) -2.82μC= -2.82e-6 C 2) q=+/- Ne 3.35e-6= N(1.6e-19) 3) N= 3.35e-6/1.6e-19 = 2.09e13 4) -2.82e-6= N(-1.6e-19) 5) N= -2.82e-6/-1.6e-19= 1.76e13 6) 2.09e13- 1.76e13 = 3.3e12 electrons. The answer key says it should be 3.86e+13 electrons, so I'm close at least but I can't figure out what I did wrong, I checked my division and conversions several times. Any help would be great! Thanks!!
 Feb 6th 2018, 11:15 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 377 nearly, but... I think you have missed a subtle key point of the question: The arrow is initially positively charged, thus has a deficit of electrons, you need to add 2.09e13 electrons just to get to zero charge, then add a further 1.76e13 electrons to get to the charge you want. TyrannosaurusWreck likes this. __________________ ~\o/~
Feb 9th 2018, 10:38 AM   #3
Junior Member

Join Date: Nov 2017
Location: The Jurassic Forests
Posts: 14
 Originally Posted by Woody I think you have missed a subtle key point of the question: The arrow is initially positively charged, thus has a deficit of electrons, you need to add 2.09e13 electrons just to get to zero charge, then add a further 1.76e13 electrons to get to the charge you want.

Thank you!!!

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