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Electric Field Strength Question watch

1. The question is:

The diagram shows four point charges, each +Q, at the corners of a square of side 2a. What is the electric ﬁ eld strength at P, the centre of the square?

The answer is zero but I don't know why, can anyone explain?

Ta
2. (Original post by RU486)
The question is:

The diagram shows four point charges, each +Q, at the corners of a square of side 2a. What is the electric ﬁ eld strength at P, the centre of the square?

The answer is zero but I don't know why, can anyone explain?

Ta
Field strength is force on a unit positive charge.
Put a small positive charge at the centre.
Which direction will the force act on it from each of the 4 charges at the corners.
These 4 forces are equal. (equal distance from the centre)
What is the resultant?
3. (Original post by Stonebridge)
Field strength is force on a unit positive charge.
Put a small positive charge at the centre.
Which direction will the force act on it from each of the 4 charges at the corners.
These 4 forces are equal. (equal distance from the centre)
What is the resultant?
Hmm I'm still confused, will the direction of the force acting on the charge in the centre be towards the corners because 2 positives will repel?
4. (Original post by RU486)
Hmm I'm still confused, will the direction of the force acting on the charge in the centre be towards the corners because 2 positives will repel?
Yes. All 4 forces are identical and act in a direction towards the corners. So the resultant is...
5. (Original post by Stonebridge)
Yes. All 4 forces are identical and act in a direction towards the corners. So the resultant is...
Ahh zero of course, thanks!

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