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How to find the number of excess electrons? 
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#1
Apr2808, 07:47 PM

P: 95

1. The problem statement, all variables and given/known data
How many excess electrons are on a ball with a charge of 4.00*10^17 C? 2. Relevant equations I know that the charge per electron is 1.60 *10^19C. 3. The attempt at a solution My textbook does not explain how to do this, but I thought I would divide>4.00*10^17 C * 1 electron/1.60*10^19. I got 2.5*10^36. The answer from the book is 2.5*10^2 electrons. I did some messing around and did this>4.00*10^17C*1 e/1.60*10^19C=2.5*10^2 electrons. What's the correct way to do this problem? Thanks in advance. 


#2
Apr2808, 07:53 PM

HW Helper
P: 1,662

Your setup is right and the units will check. But how do you divide
4.0 x 10^17 / 1.6 x 10^19 ? What is 1 / 1.6 x 10^19 ? (In fact, your check is also incorrect. You may want to review how division works with powers of ten and what negative exponents mean. 10^17 / 10^19 = 100 ; 10^17 / 10^19 = 10^36 .) 


#3
Apr2808, 07:57 PM

P: 95

uhh, i'm confused.............????



#4
Apr2808, 08:02 PM

HW Helper
P: 1,662

How to find the number of excess electrons?
You're dividing by 1.6 x .0000000000000000001 . So 4 / 1.6 is 2.5 , but what is
10^17 / 10^19 = 0.00000000000000001 / 0.0000000000000000001 ? 


#5
Apr2808, 08:15 PM

P: 95

oh i see!
10^17/10^19=100 so therefore 2.5*10^2. thanks so much! :D 


#6
Apr2808, 08:36 PM

P: 1,345

Charge is quantized so the excess charge has to be a multiple of e (elementary charge)
q=ne, where n is the number of electrons. That's why it works I believe since your textbook didn't explain it. 


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