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

Question

Four identical metal spheres have charges of q_A = -8.0 μC, q_B=-2.0 μC, q_C=+5.0 μC, and q_D=+12.0 μC.

(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 μC?

C and D

B and D

A and D

B and C

A and B

A and 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 μC?

 A+B+C

A+B+D

B+C+D

A+C+D

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

N = Number ________  Units ____

Answer 1

Using conservation of charge

a) If we add d and b we get +10 (12-2), this is then shared equally so each has +5 (Ans B+D)

b) Adding a ,c and d we get (-8 +5 + 12) = 9 shared between 3 we get +3 (Ans A, C, D)

c) We need 3 microcolumbs and each electron has -16 x 10^-19C therefore we need 1.875 x 10¹³ electrons