Two particle A and B having opp:- charges 2uC(micro coulomb) and -2uc(micro coulomb)are 1.0cm apart. a)write down the electric dipole moment of the dipole. b) Calculate the electric field a point on the axis of the dipole 1.0cm away from the centre. c) calculate the electric field at a point on the perpendicular bisector of the dipole and 1.0m away from the centre.

a. The electric dipole moment for a pair of opposite charges of magnitude q is defined as the magnitude of the charge times the distance between them and the defined direction is toward the positive charge.

 Hence, p = qd = 2*10^-6 * 1*10-2  = 2*10^-8 Cm

 

b. Electric field at a point on the axis of a dipole is given by 

 

E = 2kpr/(r^2-l^2)^2 where p is the dipole moment, r = 1cm and l = 0.5cm

E =2k* 2*10^-8*10^-2 /((1*10^-2)^2 - (0.5*10^-2)^2 )^2 =7.11k * 10^-2 N/C

c. Electric field at a point on the perpendicular bisector of a dipole is given by 

 

E = kp/(r+l)^3/2 where p is the dipole moment, r = 1cm and l = 0.5cm

E = k* 2*10^-8 /(1.5*10^-2)^3/2 = k *1.088 *10^-5 N/C