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Really haven't a clue how to go about this, it's the last question on the paper and nothing before it is anything near as complex as this.

Any help much appreciated

- Thread starter xma123
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- #1

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Really haven't a clue how to go about this, it's the last question on the paper and nothing before it is anything near as complex as this.

Any help much appreciated

- #2

Doc Al

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- #3

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Imagine the top charge is also absent. What would the field be due to the four charges?

- #4

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The 4 in the middle cancel, giving a field of either positive or negative of the single field charge above. So would the answer be option 3?

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What is the direction of j? Of the field?

- #6

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The picture is all the info given on thisWhat is the direction of j? Of the field?

- #7

Doc Al

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Good. That's the magnitude of the field, so be sure to count the direction.So due to each charge the field is E=kq/r^{2}

Yes, the 4 in the middle cancel. But I don't know what you mean by "either positive or negative". Which is it? What's the direction of the field from the top charge?The 4 in the middle cancel, giving a field of either positive or negative of the single field charge above.

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By positive or negative I was referring to the difference betweent options 3 and 4.

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Why is that?the top charge would act in the upwards of y

- #11

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Oh damn, they're positive charges, so the field acts downwards away from the top charge.Why is that?

This would give a "negative" field in the y direction and so option 4 is correct?

- #12

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Correct!they're positive charges, so the field acts downwards away from the top charge

- #13

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Thanks very much for your patience, much appreciatedCorrect!

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