Four identical metal spheres have charges of q_A = -8.0 mu C, q_B = -2.0 mu C, q

Question

Four identical metal spheres have charges of q_A = -8.0 mu C, q_B = -2.0 mu C, q_C = +5.0 mu C, and q_D = +12.0 mu 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 mu 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 mu C? (c) The final charge on each of the three separated spheres in part (b) is +3.0 mu C. How many electrons would have to be added to one of these spheres to make it electrically neutral? N = Number units

Explanation / Answer

given, there are four spheres

Qa = -8 micro C

Qb = -2 micro C

Qc = 5 micro C

Qd = 12 micro C

a. after the spheres touchm the charge redistributes

total charge on both spheres = 5*2 = 10 micro C

so when Qb and Qd touch, net charge is 10 micro C

so Qb and Qd are bought to contact

b. final charge on three spheres = 3 micro C each

total charge = 3*3 = 9 micro C

so, when Qa , Qc and Qd are bought in contact, net charge = -8 + 5 + 12 = 9 micro C

hence Qa, Qc and Qd are bought in contact

c. number of electrons top be added = n

charge on n electrons = -ne [ e = 1.6*10^-19 C]

for making the sphere electrically neutral

-ne + 3 micro C = 0

n = 3*10^-6/1.6*10^-19 = 1.875*10^13

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