Physics Review Question

Unit: Electricity and magnetism
Year: 1997 Question#: 23
Question: Three identical metal spheres are mounted on insulating stands. Initially, sphere A has a net charge of q and spheres B and C are uncharged. Sphere A is touched to sphere B and removed. Then sphere A is touched to sphere C and removed. What is the final charge on sphere A?

(1 ) q
(2 ) q/2
(3 ) q/3
(4 ) q/4

What is this question really asking?




Explanation by: Nathaniel W

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Answer 1
q

INCORRECT

Because the charge is reduced by a half, and there is a 1/4 of the original charge left in sphere C. return to top























Answer 2
q/2

INCORRECT

Because the original charge is halved twice. return to top



























Answer 3
q/3

INCORRECT

Because the orignal charge is halved each time, not 1/3. return to top


























Answer 4
q/4

CORRECT

Because the original charge is halved each time it contacts a neutral sphere, the charge on sphere C is fourthed. return to top


























What's this question really asking?

How much does the original charge get reduced each time it is touched to another un-charged object. return to top

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