Two equally charged spheres of mass 1.0 g are placed 2.0 cm apart

Physics
Tutor: None Selected Time limit: 1 Day

May 9th, 2015

We know from Coulomb's law that electrostatic force between two charges is given by -

F =  K * q1 * q2 / r^2

K is a constant and r is the distance between two charges.

Now, in the given question

q2 will be static if the force exert by q1 on q2 is equal and opposite to the force exert by Q on q2

Which means

K* q1*q2 / 20^2 = - K*Q*q2 / 10^2 (negative sign is to show opposite forces)

q1/400 = -Q / 100

q1 = -4Q

q1 = -4 * (-7.5nC)

q1 = 30 nC

Answer: B

Let me know if you need further help.

May 9th, 2015

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May 9th, 2015
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