find out mass of the charge Q, so that it remains in equilibrium for the given configuration.

(a) Derive and expression for the electric field at any point on the equatorial line of an electric dipole. (b) Two identical point charges, q each kept 2m apart in air. A third point charge Q of unknown magnitude and sign is placed on the line joining the charges such that the system remains in equilibrium. Find the position and nature of Q.

Two point charges of +q each are placed at two diagonally opposite corners of a square. Another two point charges of -q charge each are placed at the two remaining corners. Take the edge length of square equal to l. Calculate (i) work needed to move these charges slowly from an infinite separation to this given configuration. (ii) Assume that four charges at corners of the square are held fixed. Another charge Q is to be moved from infinity to the centre of this square slowly. What additional work is required to do so?

A charge +q is placed at the mid point between two unit negative charges. What should be the magnitude of the charge q so that the three charges remain in equilibrium state?

(a) Two point charges Q and 16 Q are fixed at separation d . Where should a third point charge be placed between them so that it experiences no force I.e. in equilibrium ? (b) In the previous problem , if we replace Q by - Q , where should the third charge be placed on the joining the charges so that it is equilibrium ? (c ) Three point charges Q , q and Q are placed at x = 0 , x = d//2 and x = d . Find q in terms of Q so that all charges are in equilibrium. (d) Two point charges 9 Q and 25 Q are placed at separation d . Where should a third charge q be placed between them so that all charges are in equilibrium ? Also find the value of q and its nature.

Two point charges +4q and +q are placed at a distance L apart. A third charge Q is so placed that all the three charges are in equilibrium. Then location. And magnitude of the third charge will be

Two point charges +4q and +q are placed at a distance L apart. A third charge Q is so placed that all the three charges are in equilibrium. Then location. And magnitude of the third charge will be

The ratio of q and Q so as to make the system in equilibrium is

Two particles (free to move) with charges +q and +4q are a distance L apart. A third charge is placed so that the entire system is in equilibrium. (a) Find the location, magnitude and sign of the third charge. (b) Show that the equilibrium is unstable.

Two particles (free to move) with charges +q and +4q are a distance L apart. A third charge is placed so that the entire system is in equilibrium. (a) Find the location, magnitude and sign of the third charge. (b) Show that the equilibrium is unstable.