Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Voltaic Cells: The Discovery of Current Electricity •A conductor is any material that will allow charges to flow. •An insulator is any material that will not allow charges to flow easily. •In the early 1800’s the study of static electricity was well underway. •Alessandro Volta discovered that electric charges would build up on two different conductors, (metals) if salt-water-soaked paper was placed between them. Zinc Negative charge build-up Copper Positive charge build-up Salt-watersoaked paper •The metal plates are called electrodes. •The water-soaked paper is called the electrolyte. •Volta found that by adding more layers, he could increase the amount of charge that would build up. •This is called a Voltaic Pile; a very early version of the battery. •Volta named the positive end of the pile the cathode, and the negative end the anode. •If the anode and cathode are connected by another conductor, the charges will flow from one to the other. •Volta, and many other scientists at the time, (Ben Franklin for example) assumed that the positive charge would flow out of the cell. •Conventional current, (the flow of positive charge) was widely accepted until the discovery of the electron several decades later. Charge •Charge is measured in groups called coulombs. •A coulomb is a group of 6.25x1018 charges. •The amount of charge in an object can be calculated as follows: Q Ne where, Q = amount of charge, (coulombs, “C”) N = number of charges e = elementary charge 1.6 x 10-19 C Voltage •Voltage is a measure of the energy carried a coulomb of charge. E V Q Where V = voltage, (V) E = energy, (J) Q = amount of charge, (coulombs, “C”) •Potential difference refers to the change in voltage of charges in two different parts of a circuit. Example #1 Find the potential difference of a dry cell if it does 0.35 J of work moving 1.56 x 1016 charges. Electric Current Current is the rate at which charge flows in a current. It can be found by measuring the amount of charge that passes a given point in a circuit per second. Q I t where I = current, (amps, “A”) Q = amount of charge, (C ) t = time, (s) Example #2 It takes a current of 1.0x101 A 30.0 s to boil a kettle of water. If this kettle requires 360 000 J of thermal energy, what is the potential difference across the kettle? Homework pg. 441 #1-8, 10 pg. 445 #1-6