Microcoulombs?

Question

Can someone help me with these problems? I don't understand how these are worded!

1.) Supposed two charges. each 4 micro coulombs, are located 2- cm apart. How much force is exerted on each charge?

2.)How much charge much be on one object for it to be repelled with a force of 5N by a second charge of 1 micro coulomb at a distance of 1 meter?

3.)How much is the strength of the electric field at a distance of 20 cm from a 4 microcoulomb charge?

4.)What will be the force on another 4 micro coulomb charge at the location for which you calculated the electric field in question 3 ?

Answer 1

A microcoulomb is just 1 x 10^-6 coulombs, or 0.000001 C. The key thing to remember is that an electrostatic force is equal to F = K(q1)(q2)/r^2, where K is Coulomb's constant K = 8.988 x 10^9 N-m^2/C^2, q1 is the first chage, q2 is the second charge, and r is the distance between them.

1) For example, F = (8.988 x 10^9 N-m^2/C^2)(4 x 10^-6 C)(4 x 10^-6 C) / (0.02 m)^2 = 360 N.

2) You've been given q2, r, and F, so solve algebraically for q1.

3) Field strength is E = Kq/r^2, where K is as above, and q is the given charge.

4) You can take a short cut here since you calculated E and F = Eq, where this time you use the second charge as q.