The method of images is a mathematical tool to solve the electrostatic differential problem，i.e.，introducing

image charge outside the solved space，and making the total field formed by the image charge and the

source charge satisfy the boundary. When this method is applied to the presence of adielectic，it will be found that

the choice of image charge is not unique. This also accords with the uniqueness theorem of the electrostatic problem，

because no matter what kind of image chargeis，the total field is the same. From the total field，the amount of

bound charge can be obtained. At this time，it will be further found that the reisonly one kind of image charge equal

to the amount of bound charge.