Physics Review Question

Unit: Electricity and magnetism
Year: 1992 Question#: 21
Question: Two identical spheres carry charges of +0.6 coulomb and -0.2 coulomb, respectively. If these spheres touch, the resulting charge on the first will be

(1 ) +0.8 C
(2 ) +0.2 C
(3 ) -0.3 C
(4 ) +0.4 C

What is this question really asking?



Explanation by: Dana H

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Answer 1
+O.8C

Incorrect, It looks like you simply added the two numbers together. There would have to be a +1.8 C charge on the sphere to get +.8C charge left on the first one. return to top























Answer 2
+0.8 C Correct, after adding +0.6C and -0.2C coulombs you'd get +0.4C then dividing by 2 (two spheres) the result is +0.2C on each sphere. return to top

Answer 3
-0.3C Incorrect, there would have to be more negatives than positives in order to have a negative charge on the first sphere. return to top

Answer 4
+0.4C

Incorrect, the total charge between both the spheres after they touch is +0.4C but that charge would evenly distribute across both spheres so each should only have half of the total.
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What's this question really asking?

What is the charge of the first sphere after they touch? return to top