Four identical metal spheres have charges of q A = -8.0 C, q B =-2.0 C, q C =+5.

Question

Four identical metal spheres have charges of qA = -8.0 C, qB=-2.0 C, qC=+5.0 C, and qD=+12.0 C.

(a) Two of the spheres are brought together so they touch, and then they are separated. Which spheres are they, if the final charge on each one is +5.0 C?

(b) In a similar manner, which three spheres are brought together and then separated, if the final charge on each of the three is +3.0 C?

(c) The final charge on each of the three separated spheres in part (b) is +3.0 C. How many electrons would have to be added to one of these spheres to make it electrically neutral?

Explanation / Answer

a)Take 2nd and 4th and add them we get -2+12 =10 and divide by 2

5, therefore these are the charge spheres which gives final charge on each sphere is +5.0 C

b) Take the first three and add the charges
–8–2+5 totals –5
when they are separated, each one gets 1/3, so each one gets –3/5 µC in this case

last three, –2+5+12 = 15
divide by 3, that is 5 µC each

1,3,4th ones
–8+5+12 = 9
9/3 = 3 µC, this is the ones.

c) The electrons that would have to be added to one of +3.0 C spheres to make it electrically neutral are

n= +3.0 x 10-6 C /1.6 x 10-19 C = 1.875 x 1013 electrons

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