Two point charges

  • Thread starter kbyws37
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  • #1
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Two point charges are located on the x−axis: a charge of +7.80 nC at x = 0 and an unknown charge q at x = 0.50 m. No other charges are nearby. If the electric field is zero at the point x = 1.0 m, what is q?


I separated the charges.
q1 = +7.80 nC
q2 = unknown

I am confused about the last part of the question where the electric field is zero.

Would I use the equation
E= k(Q) / r^2

(Correct answer is: -1.95 nC)
 

Answers and Replies

  • #2
Hootenanny
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Yes you would use the defintion of the electric field to set up an equation of the form;

[tex]E_1 + E_2 = 0[/tex]
 
  • #3
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What are the electric field vectors at x=1m due to Q1 and Q2?
 
  • #4
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I'm not getting the right answer.
I did...

0 = ((8.99x10^9)(7.80)) / 0.5^2) + ((8.99x10^9)(q)) / 0.5^2)

which does not equal zero.

I think I still need to do something else.. something about point x = 1.0m ?
 
  • #5
Hootenanny
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Indeed, how far is the first charge (q1) located from the point of zero electric field?
 
  • #6
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Indeed, how far is the first charge (q1) located from the point of zero electric field?

it would be
1.0 meter
 
  • #7
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Check your expession for electric feild due to q1.
 
  • #8
Hootenanny
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it would be
1.0 meter
That's correct, not 0.5m as you had previously :wink:
 

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