Electrical Conductors and Insulators Battery Lamp Test terminals In this presentation you will: identify electrical conductors and insulators Next > Sunday, March 17, 13 Introduction Electrical conductors are Lamp materials that Battery allow electric current to flow. Typical conductive materials include Test silver, copper, and terminals steel. Copper Steel Silver Next > Sunday, March 17, 13 Introduction Electrical insulators are materials that do not allow electric current to flow. Plastic Typical insulator materials include plastic, wood, and ceramic. Wood Materials have different levels of conduction or insulation. For example, silver and steel are both conductors, but silver is a better conductor. Ceramic Next > Sunday, March 17, 13 Atomic Structure All materials are made from atoms. We can model the appearance of an atom by having a central nucleus made of protons and neutrons. Electrons, which have a tiny electrical charge, move around the central nucleus in orbits. Each orbit can have a maximum number of electrons. By knowing how many electrons there are, you can work out their distribution. Next > Sunday, March 17, 13 Atomic Structure An electron remains in orbit around the nucleus because it is oppositely charged to the nucleus. “Unlike charges attract, _ like charges repel“ -Law of Charges. _ + + _ _ + The further out the + + + + orbit is, the weaker the _ force holding the _ electron in place. _ The outermost electron(s) may be very weakly bound to an atom. Next > Sunday, March 17, 13 Electrons in Atoms Atoms are very close to each other in a solid, so it is quite common for an electron in an outer orbit to move to a neighbor’s outer orbit if there is space. If an electron leaves an outer - orbit, it leaves a space behind. - + - The atom now has an overall - - positive charge, and it will + quickly attract an electron in to fill the space. In some solids, electrons are moving between atoms all the time. Next > Sunday, March 17, 13 Conduction in Solids If a source of electromotive force (EMF), such as a battery, is connected across a solid, all electrons will now be under the influence of an external field. If the field is strong enough, any loosely bound electrons will start to move toward the positive battery terminal. Next > Sunday, March 17, 13 Conduction in Solids The loosely bound electrons may well be captured by atoms as they pass, but if they are only loosely held, they could be released again. Materials that are classed as good conductors will easily allow the movement of these free electrons. Next > Sunday, March 17, 13 Question 1 Why is silver a very good electrical conductor? A) It stops electrons from moving between atoms B) It allows electrons to move easily between atoms C) It is shiny Next > Sunday, March 17, 13 Question 1 Why is silver a very good electrical conductor? A) It stops electrons from moving between atoms B) It allows electrons to move easily between atoms C) It is shiny Next > Sunday, March 17, 13 Insulators Resistance is the opposite of conductance. Materials that are good conductors of electricity have a low resistance. Silver Materials that are poor conductors of electricity have a high resistance. Plastic Next > Sunday, March 17, 13 Insulators Conductor - silver If we look at the atomic structure of metals that are good conductors, we see that each has only a Single electron single electron in the in silver atom outermost orbit. structure In addition, this outer electron Insulator - phosphorus is relatively easy to remove. Materials that are good insulators do not have a single free electron in the outermost orbit, therefore, have a high resistance. Next > Sunday, March 17, 13 Question 2 Which atomic structure would produce the best insulator? A) C) B) D) Next > Sunday, March 17, 13 Question 2 Which atomic structure would produce the best insulator? A) C) B) D) Next > Sunday, March 17, 13 Uses of Conductors and Insulators Conductors are used in applications where we want electricity to flow, for example, in power cables. Insulators are used in applications where we need to be protected Insulator from possible contact Conductor with electricity, for example, the shielding around cables. Next > Sunday, March 17, 13 Electrocution! Providing a conduction pathway for electricity can be fatal. The human body is made mostly of water and is an electrical conductor, although a poor one. Many people have died by becoming the conduction pathway between an electricity supply and the ground. Next > Sunday, March 17, 13 Electrocution! Even though air is a poor electrical conductor, if the voltage is high enough, lightning will cause a conduction pathway for electricity to flow to the ground. Some tall buildings have lightning conductors to deliberately channel the electricity safely to the ground. Next > Sunday, March 17, 13 Question 3 Which of the following items need to be manufactured from electrically insulating material to help prevent electrocution? A) The plug cover on a desk lamp powered by an electrical outlet B) The case of a hair dryer C) The motor cover of a desk fan D) All of the above Next > Sunday, March 17, 13 Question 3 Which of the following items need to be manufactured from electrically insulating material to help prevent electrocution? A) The plug cover on a desk lamp powered by an electrical outlet B) The case of a hair dryer C) The motor cover of a desk fan D) All of the above Next > Sunday, March 17, 13 Summary In this presentation you have seen: what makes a material an electrical conductor or insulator examples of electrical conductors and insulators End > Sunday, March 17, 13.