Answer to Question #21866 in Electromagnetism for divya rawal
four charges each equal to Q are placed at the four corners of a square q and a charge q is placed ct the centre of the square. if the system is in equilibrium then what is the value of q ?
System is in equilibrium when resultant of all forcesis 0. That means: forces from charges Q must be balanced by forcefrom charge q. So, we will find q from this condition. Forces from Q-s are: k Q^2/(2a^2) + 2 k Q^2/a^2 = 2.5 kQ^2/a^2 where a is a side of a square Force from q is kQq / (a^2/2) = 2kQq/a^2
So we find 2kQq/a^2 = -2.5 kQ^2/a^2 2q =- 2.5Q q= -2.5/2 Q = -1.25 Q answer is q=-1.25*Q