Suppose you have two electrical charges with equal magnitude, but you don't know what the sign of their charge is. As you bring them closer, you notice the electric potential energy between them increases. What can you determine about the sign of each charge?
Suppose you have two electrical charges with equal magnitude, but you don't know what the sign of their charge is. As you bring them closer, you notice the electric potential energy between them increases. What can you determine about the sign of each charge?
None of the above |
Impossible scenario; energy remains constant |
The charges have opposite sign |
The charges have the same sign |
Answer - The charges have the same sign.
The electric potential energy of two identical charges Q can be
written as, E = kQ2/r
Where k = 1/4o
and r is the distance between the charges.
Case 1 - The charges have opposite sign
E = [k * (+Q) * (-Q)] / r OR [k * (-Q) * (+Q)] / r
= - kQ2/r
As we bring the charges closer, r decreases and the magnitude of E
become more negative. Thus E decreases.
Case 2 - The charges have the same sign
E = [k * (+Q) * (+Q)] / r OR [k * (-Q) * (-Q)] / r
= kQ2/r
As we bring the charges closer, r decreases and E increases as
stated in the question.
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