Physics questions on Coulomb\'s Law? 1. Two equally charged spheres attract each
ID: 1342799 • Letter: P
Question
Physics questions on Coulomb's Law?
1. Two equally charged spheres attract each other. If the charges on the spheres are halved, what distance must the charges be separated to have the same attracted force? What if the charges are doubled?
2. Sphere A and sphere B are separated by some distance r. Sphere A has a charge of 3.1 C Coulombs and attracts sphere B with 1.6 N of force. The spheres are then touched together and then returned to a separation of distance r. They now repel with a force of 1.2 N. What was the original charge on sphere B? What is the distance r? You will have two sets of answers.
Explanation / Answer
1. F = kqq / d^2
now q' = q/2
and F' = F
F' = kq'q' / d'^2 = F = kqq/d^2
(q/2)(q/2) / d'^2 = q^2 / d^2
d'^2 = d^2 / 4
d' = d/2
distance also halved.
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2) suppose charge on B is - q uC.
then F = kq1q2/d^2
1.6 = (9 x 10^9 x 3.1 x 10^-6 x 10^-6 x q / r^2 )
q/r^2 = 57.35
now when spheers are touched.
charge on each sphere will be same.
q' = (3.1 -q) x 10^-6 /2
now F = kq^2 / r^2
1.2 = 9 x 10^-9 x (q +3.1)^2 /4 x 10^-12 / r^2
(q - 3.1)^2 / r^2 = 533.33
putiing r^2 = q/57.35
(q^2 - 6.2q + 9.61 ) / (q/57.35) = 533.33
q^2 - 6.2q + 9.61 = 9.30q
q^2 -15.50q + 9.61 = 0
q = 0.647 and 14.85
ANs : q = - 0.647 uC and -14.85 uC
for r , 1.6 = 9 x 10^9 x 3.1 x 0.647 x 10^-12 / r^2 and 1.6 = 9 x 10^9 x 3.1 x 14.85 x 10^-12 / r^2
r = 0.106 m r = 0.509 m