Two equal point charges are separated by a distance d$.$ If a third test charge is inserted at a point exactly midway between the two charges, what is the amount of net force the third charge would experience?

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State what happens when:$-$

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$$ i$.$ Two positive charges are brought into close proximity to each other.

$$ ii$.$ Two negative charges are brought into close proximity to each other.

What are the units for resistivity and for current density?

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