Coulombs Law There is an electrical force that exists between any two objects We can measure this force using Coulombs Law Coulombs Law It is important to remember that Coulombs Law is an inverse-square relationship with distance This means that the force is going to be inversely proportional to the square of the distance between the two objects Coulombs Law Coulombs Law is a formula developed by French physicist Charles Coulomb in the late 1700s. The formula can be seen here to the right. Coulombs Law It is important to understand the k is a constant. k is always going to be 9,000,000,000 which is the same as 9 x 10^9 Coulombs Law q 1 and q 2 are the quantities of charge of each particle Sometimes instead of using the numbers 1 and 2 show the difference between the two we use the letters p and e to represent a proton and an electron Coulombs Law Units The unit of charge in this formula represented by q is measured in Coulombs (C). Coulombs Law Units It is important to remember that 1C is not the charge quantity for 1 electron. It is the charge quantity for 6.24 x 10^18 electrons This is because approximately 6.24 x 10^18 electrons pass through a 100 watt bulb in 1 second Try It! The hydrogen atom has the simplest structure of all atoms. Its proton is approximately 5.3 x 10^-11 m. The proton charge is 1.6 x 10^-19 C The electron charge is -1.6 x 10^-19 C What is the quantity of force between them? Are they attractive or repellent? Conductors and Insulators Electrons move more easily in some materials than in others In metallic materials electrons are not tightly bound to the nucleus but instead are free to roam. This is because they are good conductors. Conductors and Insulators Metals are good conductors because the electrons are said to be loose All substances can be arranged in order of their ability to conduct electrical charges Those at the top of the list are conductors and those at the bottom are insulators. Examples of Conductors and Insulators An example of an insulator would be a metal such as copper. An example of an insulator would be glass. The conductivity of copper is approximately a million, billion (1.0 x 10^15) times greater than glass. Conductors and Insulators A substance is classified as a conductor or insulator based upon its ability to hold their electrons Semiconductors Some materials are called semiconductors A semiconductor is a material that can sometimes be a conductor and other times be an insulator What do you think is an example of a semiconductor? Superconductors A superconductors are materials that will achieve infinite conductivity only when placed under temperatures of absolute 0. (0 degrees Kelvin) How we create charges There are three ways we can create charge in objects Friction Contact Induction Charging by Friction We are most familiar with charging an object by friction and contact To charge by friction requires you to rub an object vigorously and subsequently contact it with something else Charging by Contact Electrons can be transferred from one material to another simply by touching This is called charging by contact Charging by Contact If the object is a good conductor then the charge will spread to all parts of its surface. Charging by Induction When charging by induction we start with two objects that are touching each other Because they are touched together they are treated as a single non charged entity Charging by induction If we take a negatively charged object like a balloon and bring it next to the two spheres we are inducing a charge This is because all of the electrons will be repelled to the opposite sphere Charging by Induction If we induce a charge on spheres A and B like shown in the diagrams you just saw would they be exactly equal but opposite?