Two free point charges are at a distance l apart. Their values are: q1=+q and q2=+4q. A third charge is placed so that the system is in equilibrium. Find the location and value of the third charge.

An infinite line of charge produces a field of 45000 N/C at a distance l= 2m. Calculate the linear charge density. What system of units are you using?

What is the amount of energy required to assemble the following configuration of charges: q1= 1 microC, q2= -1 microC, q3= 2 microC, placed respectively at x=0, x=2m, x=3m, on the x-axis?

A capacitor with capacity C1 is connected in parallel with a capacitor C2. A potential difference is applied across the pair. What is the charge on each capacitor?