Materials that are not good at conducting electric current are called insulators, which are also called dielectrics. They have very high electrical resistivity. There is no absolute boundary between an insulator and a conductor. An insulator can be transformed into a conductor under certain conditions.
What do insulators have?
The characteristic of insulators is that the positive and negative charges in the molecules are tightly bound, and there are very few electrically charged particles that can move freely, with a high resistivity of about 10-10 ohms per meter M. Therefore, in general, the macroscopic current generated by the movement of free charges under the action of an external electric field can be ignored and considered as non-conductive materials.
There are many types of insulators, including solid insulators such as plastic, rubber, glass, ceramics, and so on; Liquid insulators include various natural mineral oils, silicone oil, trichlorobenzene, etc; Gas insulators include air, carbon dioxide, sulfur hexafluoride, etc.
Glass rods, glasses, plastic rulers, rubbers, wooden blocks, sharp knife handles, cooking oil, etc. are common insulators in daily life.
Relationship between insulator and conductor
Insulators and conductors are not absolute, and there is no insurmountable gap between them. The difference between the two is mainly related to the amount of electric charge that can move freely inside, but also to external conditions (such as voltage, temperature, etc.). Insulated objects at room temperature, when the temperature rises to a certain degree, will be converted into conductors due to the increase in the amount of freely movable charges.