Electric Field at Point P in an Equilateral Triangle

[Kathi201]

Three positive and equal charges Q1, Q2, and Q3 are at the corners of an equilateral triangle. Point P is at the midpoint of the line between Q1 and Q3 (the middle of the bottom of the equilateral triangle). The electric field at P is
A.zero
b. not zero and directed along the line from P to Q3
c.not zero and is directed along the line from P to Q2
d. not zero and is directed along the line from Q1 to Q2
E.none of these are correct

My thinking is that the answer is zero. I know that the electric field points away from positive charges so if Q1 and Q3 are at the bottom of the equilateral triangle the P is in the middle they are going to direct the opposite way and cancel each other out.

Anybody know if this is correct or have a reason why another answer would be correct?

 

[alphysicist]

Hi Kathi201,

Three positive and equal charges Q1, Q2, and Q3 are at the corners of an equilateral triangle. Point P is at the midpoint of the line between Q1 and Q3 (the middle of the bottom of the equilateral triangle). The electric field at P is
A.zero
b. not zero and directed along the line from P to Q3
c.not zero and is directed along the line from P to Q2
d. not zero and is directed along the line from Q1 to Q2
E.none of these are correct

My thinking is that the answer is zero. I know that the electric field points away from positive charges so if Q1 and Q3 are at the bottom of the equilateral triangle the P is in the middle they are going to direct the opposite way and cancel each other out.

You're right that the electric field from Q1 and Q3 are going to cancel. But what about the field at P from Q2?

 

[Kathi201]

Oh Ok thank you I forgot about Charge Q2. So the electric field at P is going to be directed along the line from P to Q2.

Thanks for your help