Direction of electric field

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  • #1
acherentia
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Homework Statement



three equal and positive charges q are located equidistant from the origin as shown http://s966.photobucket.com/albums/ae146/acherentia/?action=view&current=directionofanelectricfield.jpg . Is the direction of the electric field at the origin a) along x, b)along -x, c) along +y d) along -y

Homework Equations



The electric field is directed outward away from Q when Q is positive.

The Attempt at a Solution



Do the field lines along the x-axis emerging from the charges on the x-axis cancel or enhance each other at the origin?

Do I have to do vector addition on the x-axis to solve this problem?
 

Answers and Replies

  • #2
berkeman
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Homework Statement



three equal and positive charges q are located equidistant from the origin as shown http://s966.photobucket.com/albums/ae146/acherentia/?action=view&current=directionofanelectricfield.jpg . Is the direction of the electric field at the origin a) along x, b)along -x, c) along +y d) along -y

Homework Equations



The electric field is directed outward away from Q when Q is positive.

The Attempt at a Solution



Do the field lines along the x-axis emerging from the charges on the x-axis cancel or enhance each other at the origin?

Do I have to do vector addition on the x-axis to solve this problem?

Just do the vector addition at the origin. What are the 3 E-field vectors at the origin? (magnitudes and directions)
 
  • #3
acherentia
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for the charge on the -x axis : kQ/r^3 x ri
for the charge on the +x axis: kQ/r^3 x r-i
for the charge on the +y axis: kQ/r^3 x r-j

so the charges that are sitting on the x-axis will cancel out. how do i write that in a more mathematical way?
 
  • #4
berkeman
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64,187
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for the charge on the -x axis : kQ/r^3 x ri
for the charge on the +x axis: kQ/r^3 x r-i
for the charge on the +y axis: kQ/r^3 x r-j

so the charges that are sitting on the x-axis will cancel out. how do i write that in a more mathematical way?

Correct. In general, you would write the vector sum in rectangular coordinates. Express each individual vector as the sum of its x and y components (using the i,j vector notation, or x-hat, y-hat, etc.), and show the sum of them as a sum of x components and y components, still in rectangular vector notation.

And in this problem, it's just multiple choice anyway. Which is your answer?
 
  • #5
acherentia
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The answer is d, along -y
 
  • #6
berkeman
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