An electric dipole is formed from two charges,+/- q ?

Question

An electric dipole is formed from two charges,+/- q , spaced 1.40 cm apart. The dipole is at the origin, oriented along the y-axis. The electric field strength at the point (x,y) = (0cm,10cm) is 390 N/C.

a) What is the charge q? Give your answer in nC.

b) What is the electric field strength at the point (x,y) = (10cm,0cm)?

Answer 1

a)

E = p/(2πεz^3)

390 N/C = q(1.40e-2 m)/(2πε*(10e-2 m)^3)

q = 1.55e-9 C = 1.55 nC

b)

View the dipole as two separate charges. Since the point is on the x-axis, the electric field strengths are equal. The magnitude of the vector sum is:

E = kq*2sin θ/r^2

= 2(8.99e9 N*m^2/C^2)(1.55e-9 C)*sin(arctan(.7/10))/(10e-2 m)^2 = 194.6 N/C