Calculating Electric Field (what am i doing wrong?)

In summary, the conversation is about a problem with point charges and calculating the electric field at a specific point. The speaker discusses their method of converting distances to meters and calculating the electric fields at each point, and notes that the homework website is saying the answer is wrong. They also mention checking the direction of the electric fields and the units that the answer should be in.
  • #1
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I believe this may be a problem with the website where I do my homework. Please check my solution and see if there is a mistake or if I am missing something. The following is the arrangement of point charges in the problem:

8.26 micro C ---2.93 cm---> P1 ---1.59 cm ---> 4.94 micro C ---2.73 cm--->-1.23 micro C

What is the electric field at point P1? Coulomb's constant is 8.98755 Nm^2/C^2.

I convert all distances to meters which gives:
r1 = 2.93 cm = .0293 m
r2 = 1.59 cm = .0159 m
r3 = 1.59 cm + 2.73 cm = 4.32 cm = .0432 m

Since all points are on the X-axis only, I do not have to worry about any Y-axis components. I perform the following steps:

E1 = (8.98755e+9 Nm^2/C^2)(8.26e-6 C)/.0293 m^2 = +86474115.0159 N/C
E2 = (8.98755e+9 Nm^2/C^2)(4.94e-6 C)/.0159 m^2 = -175620018.987 N/C
E3 = (8.98755e+9 Nm^2/C^2)(1.23e-6 C)/.0432m^2 = +5923507.4267 N/C

E1-E2+E3 = -83222396.5444 N/C

My homework website says the answer is wrong. We do not need to worry a obout significant figures in the answer. What errors can you see, or what am I missing.
 
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  • #2
What units is it asking for the answer in? I'm doing similar homework and it asks for the answer in kN/C not N/C.
 
  • #3
Answer should be in N/C
 
  • #4
OK, the next thing I'd check is the direction of your electric fields. Remember that for negative charge points, the fields go toward the points and for positive charge points, the fields go away from the points.
 

What is the equation for calculating electric field?

The equation for calculating electric field is E = k(Q/r^2), where E is the electric field, k is Coulomb's constant, Q is the magnitude of the charge, and r is the distance from the charge.

What units are used for electric field?

Electric field is typically measured in newtons per coulomb (N/C) or volts per meter (V/m).

Do I need to consider the direction of the electric field?

Yes, the direction of the electric field is important and is typically indicated with a vector arrow. The direction of the electric field is in the direction that a positive test charge would move if placed in the field.

What is the significance of Coulomb's constant in the electric field equation?

Coulomb's constant, represented by the letter k, is a proportionality constant that relates the magnitude of the charge to the strength of the electric field. It is equal to 8.99 x 10^9 Nm^2/C^2.

Why might my calculated electric field value differ from the expected value?

There are several factors that could lead to a discrepancy between the calculated and expected electric field values, such as experimental error, incorrect units, or not accounting for the direction of the electric field. It is important to double-check all calculations and make sure all variables are accounted for.

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