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Question 15 of 36

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SAT Subject Test

Two small conducting spheres are identical except that sphere X has a charge of negative 10 microcoulombs and sphere Y has a charge of plus 6 microcoulombs. After the spheres are brought in contact and then separated, what is the charge on each sphere, in microcoulombs?

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Sphere X Sphere Y
-4 0
Correct Answer: 
No
Sphere X Sphere Y
-2 -2
Correct Answer: 
Yes
Sphere X Sphere Y
+2 -2
Correct Answer: 
No
Sphere X Sphere Y
+4 0
Correct Answer: 
No
Sphere X Sphere Y
+6 -10
Correct Answer: 
No

The correct answer is negative 2 microcolumbs on each sphere. Excess charge on a number of conductors in contact will be distributed in such a way that the electric potential on the surface of the conductors is the same everywhere. If the conductors are identical, this requires that an equal amount of excess charge reside on both conductors. The net excess charge on these two spheres is negative 4 microcolumbs left parenthesis plus 6 plus left parenthesis negative 10 right parenthesis right parenthesis. Since charge is conserved, when the excess charge is shared equally each sphere will carry negative 2 microcolumbs.

Question Difficulty: 
medium