Potential Difference LESSON 7 NOVEMBER 15 TH 2010

Potential Difference LESSON 7 NOVEMBER 15 TH, 2010

Potential Difference Each electron has electric potential energy. Potential energy is the energy stored in an object. Example: An apple hanging from a low. The apple has potential energy because of its position above the ground. If the apple falls down, it will convert its stored energy, or potential energy, into motion. An apple at a higher branch. It would have even more potential energy to convert.

Potential Difference A battery has chemical potential energy in the electrolyte in its electrochemical cells. The chemicals in the electrolyte react with the electrodes. This causes a difference in the amount of electrons between the two terminals.

Potential Difference One terminal in a battery has mainly negative charges (electrons). The other terminal has mainly positive charges. The negative charges are electrons, which can move are attracted to the positive charges at the positive terminal.

Potential Difference If a conductor, such as a copper wire, is connected to both terminals, then the electrons flow from the negative terminal to the positive terminal. The difference in electric potential energy between two points in a circuit is called the potential difference or voltage (V).

Potential Difference This difference causes current to flow in a closed circuit. The higher the potential difference in a circuit, the greater the potential energy of each electron.

Measuring Potential Difference The potential difference between two locations in a circuit is measured with a voltmeter.

Measuring Potential Difference Example: Connecting wires from a negative terminal on a battery across a voltmeter and then back to the positive terminal. The voltmeter would then display the potential difference of the battery. The SI unit for measuring potential difference is the volt (V).

Electrochemical Cells – Batteries A battery is a combination of electrochemical cells. Each electrochemical cell is a package of chemicals that converts chemical energy into electrical energy that is stored in charged particles. A simple electrochemical cell includes an electrolyte and two electrodes.

Electrochemical Cells – Batteries An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions. An ion is an atom or a group of atoms that has become electrically charged by losing or gaining electrons. Sulphuric acid is an example of an electrolyte.

Electrochemical Cells – Batteries Electrodes are metal strips that react with the electrolyte. Two different electrodes, such as zinc and copper, are used in a battery. The electrodes and electrolyte react causing one electrode to collect and the other to lose electrons.

Wet Cells and Dry Cells An electrochemical cell that has a liquid electrolyte is called a wet cell. Wet cells are often used as an energy source for cars and other motorized vehicles.

An electrochemical cell that uses a paste instead of a liquid electrolyte is called a dry cell.

Wet Cells and Dry Cells An electrochemical cell that uses a paste instead of a liquid electrolyte is called a dry cell. Dry cells are used in flashlights, hand -held video game devices, cameras, and watches. Each electrode in a dry cell or battery can also be called a terminal. Terminals are the end points in a cell or battery where we make a connection

Recycling and Recharging Dry Cells Eventually, the chemicals in a dry cell are used up and can no longer separate charges. Dry cells should be recycle rather than discarded. Dry cells can contain toxic materials, such as the heavy metals nickel, cadmium, and lead. Household dry cells and batteries are responsible for over 50 percent of all the heavy metals found in landfills.

Recycling and Recharging Dry Cells Some dry cells are rechargeable cells. Chemical reactions in a rechargeable cell can be reversed by using an external energy source to run electricity back through the cell. The reversed flow of electrons restores the reactants that are used up when the cell produces electricity

Recycling and Recharging Dry Cells Since rechargeable dry cells can be reused many times, they have less impact on the environment than non-rechargeable dry cells.

Fuel Cells A fuel cell is an electrochemical cell that generates electricity directly from a chemical reaction with a fuel, such as hydrogen. The cell is not used up like an ordinary cell would be because as the electricity is produced, more fuel is added.

Fuel Cells Much of the energy produced by fuel cells is wasted as heat, but their design continues to be refined. Fuel cells are used in electric vehicles and may one day be used in smaller devices such as laptop computers.

Fuel Cells

Questions 1. How is current electricity different from static electricity? I (1) 2. What is the difference between an electrolyte and an electrode? I (1) 3. Why should dry cells be recycled rather than thrown in the trash? K (1 4. What is another name for stored energy? K (1) 5. What does potential difference measure? K (1)