The very basics of electricity. Moving electrons and storing them for when you want them

Transcription

1 The very basics of electricity Moving electrons and storing them for when you want them

2 Static Around 600 BCE, it was discovered that if amber (fossilized tree sap) is rubbed with cat s fur (meow!) it can be made able to pick up light objects, such as feathers It was believed that friction turned the amber magnetic, similarly to the ore called magnetite In 1600, the term electricus was used to described objects that, like amber, could pick up things when rubbed with fur Electricus means like amber

3 Nature likes neutral Removing electrons from a substance makes it positive-charged and immediately become highly attractive to any neutrally charged substance The electrons will want to flow from the neutral object (or negative-charged object) to the positive object Electrons cannot travel through nothing! If the objects are touching or if a conductor is available the electrons will flow until the charge difference is evened out If they can t then you have a static charge

4 Static means staying in one place, not moving Static electricity can be generated easily by friction Rub a balloon on your head Wear socks on a carpet and drag your feet Rub a plastic rod with your cat Static Electricity

5 Static build up Charge differences can accumulate until they release all at once such as when they find a conductor (or some other way to equilibrate or ground ) A static shock is when something has had electrons stripped away so that is becomes highly attractive to anything with electrons The electrons then flow extremely rapidly to ground themselves and equal out the charge imbalance

6 Not actually my daughter

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8 Convection current create charge differentials!

9 review Review we re talking about electrons moving, and that means we need to remember things terms like force and energy What are the units for these things and what do they mean?

10 Coulomb s Law Charles Augustin de Coulomb discovered that the force any charged particle exerts on another charged particle is determined by an inverse square law The law details: Any charged thing will make any other charged thing move How much energy it moves with is based only on how charged they are, and how far apart they are Force of interaction A constant Amount of charge of thing 1 Distance between charged particles Amount of charge of thing 2 Newton s gravitational laws are identical!!!

11 Gee that s great, Mr. K but where is this going? If you are going to have electricity you need to have a way to push or pull electrons. This first part was to establish what electricity is and why electrons move!

12 Review and moving forward The Coulomb Force is the force of electrostatic interaction what does this mean? How does the inverse square law describe this force? The Coulomb is the Standard Unit of electrical charge (symbol is C)

13 Storing static charge to use later If you have created a charge, you can store the capacity of that charge in a device called a capacitor An early version of this was called a Leyden Jar Capacitors are still used to start motors, provide power, regulate current flow in circuits, etc

14 Leyden jars Benjamin Franklin put this to use, trying to literally catch lightning in a bottle By showing that Lightning could charge a Leyden jar, lightning was electricity What is this thing on the ground, I wonder?

15 Leyden jars and batteries Leyden jars could store quite a lot of power "I would not take a second shock for the kingdom of France. An early experimenter with Leyden Jars, who felt the shock of a Leyden jar he d made Benjamin Franklin noted that a number of Leyden jars together would be like a battery of cannon

16 The first battery In 1800, Alessandro Volta built the first chemical battery Discs of Copper and Zinc separated by paper soaked in saltwater, called a Voltaic Pile When the top and bottom contacts were connected by wire, electrical current would flow through that wire Symbol for a battery in a circuit diagram

17 A Cu-Zn Voltaic cell Electrons begin at the anode Here, Zinc prefers to be positive, so it ditches its electrons, which are now free Copper loves electrons (more than Zinc), so it happily accepts Zinc s So electrons flow from anode to cathode in a typical battery (they don t all have to be Zn-Cu) The potential energy of the battery is measured in Volts

18 The Volt An SI unit that describes the electrical potential energy per unit of charge (given in Joules per Coulomb) 1 V = 1 J/C It is the push on the electrical charge moving through an electrical current (such as along a wire in a circuit) are they being pushed a lot? Pushed a little? Is the current a huge, rushing river or a little babbling brook?

19 Coppertop duh! Cathode Anode

20 Batteries versus capacitors Both store charge Capacitors can be recharged, and discharge themselves extremely quickly Battery s (the kind we ve seen) cannot be recharged, their potential comes from chemical reactions. Once the chemical reagents run out, the battery is dead