Electric Field with three charges

AI Thread Summary
The discussion revolves around calculating the electric field at a specific point near three charges arranged on a horizontal line. The user has correctly identified the need to calculate the electric fields E1, E2, and E3 for the respective charges, using the Coulomb's law formula. There is confusion regarding whether to add or subtract the electric fields due to the repulsive and attractive forces between the charges. The user has calculated E1 and E2 as positive and E3 as negative, indicating their directions based on charge interactions. Clarification is sought on the correct approach to combine these electric fields while considering their directions.
rinarez7
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1. Homework Statement
Consider 3 charges along a horizontal line as shown:
8.72e-6 C (+) ___4.16cm____2.45e-6 C (+)______3.18cm_____-1.46e-6C (-)
The acceleration due to gravity is 9.8 m/s^2
The Coulomb Constant is 8.98755e 9 Nm^2/ C^2
What is the electric field at a point 2.18 cm to the left of the middle charge? Answer in units fo N/C


2. Homework Equations
Q1= 8.72e-6 C , r= .0198m (.0416m-.0218m)
Q2= 2.45e-6 C, r= .0218m

E1= k Q1 / r^2
E2= k Q2/ r^2

3. The Attempt at a Solution
I converted all of my units first to C and meters.
Then I solved for E1 and E2 separately.
Once I had E1 and E2, I added the two together. But I can't seem to get the right answer.
Am I supposed to subtract them instead becasue Q1 and Q2 are both positive and therefore will repel each other?
 
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You have THREE charges causing electric fields, so you need to find E1, E2 and E3.
Add them together, keeping direction in mind!
 
so I calculated E1 = 1.999e8, E2 as 4.633e5, and E3 as -3.657e6
Am I correct to say then that, E1 and E3 are negative (pointing to the left) and E2 is positive?
E1(+)<----X----->E2 (+)-----><------E3 (-)
 
E1 to the right (away from a positive charge), E2 to the left (away from a positive charge), E3 to the right (toward a negative charge).
 
Thank you!
 
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