import matplotlib.pyplot as plt
import numpy as np
k=9.0e9
q=1.9e-19
d=1.0e1
t=np.linspace(0,2*np.pi,10000)
i=1
V=V=(3*k*q*(d**2)/(2*(i**3)))*np.cos(2*t)
plt.plot(t,V,color='black')
plt.xlabel('theta')
plt.ylabel('Potential')
plt.show()