Finding the magnitude of an electric field.

AI Thread Summary
To find the electric field magnitude midway between a -8.1μC and an 8.9μC charge, the formula E=k/r^2(Q1+Q2) is used. The individual electric fields from each charge need to be calculated correctly, considering their directions; the field from the negative charge points toward it while the field from the positive charge points away. The user mistakenly used the total distance of 8.0 cm instead of the correct distance of 4.0 cm from each charge to the midpoint. The calculated electric field value of 2.4e7 N/C is incorrect due to this error in distance. Accurate calculations are crucial for determining the correct electric field magnitude and direction.
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Homework Statement


Determine the magnitude of the electric field at a point midway between a -8.1μC and a 8.9μC charge 8.0cm apart. Assume no other charges are nearby.
Determine the direction.
(Answer in two sig figs.)

Homework Equations


E=k/r^2(Q1+Q2)

The Attempt at a Solution



I drew this: -8.1---------p----------8.9

This is what I think I'm supposed to do.

The field due to -8.1 charge points toward it.
The field due to 8.9 points away. So they are both pointing towards the negative charge?

so E=k/.08^2(8.1e-6+8.9e-6)=2.4e7 N/C but this is incorrect. Please explain why! Thanks.
 
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I want to slap myself now...is it because r=.04m? Want assurance because I'm on my last strike.
 

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