Transcript File
Introduction to Current Electricity The Flow of Electrons • Unlike static electricity, current electricity refers to electric charges (electrons) that flow through a conductor in a controlled way. • What allows electrons to move? CONDUCTORS Electric Circuits • Electric Circuit – a continuous path in which electrons can flow. How does it work? Your MP3 Player uses an circuit to operate. Electrons flow from the battery through the conductors and other electrical components to the player. Eventually, the electrons will return to the battery. This flow of electrons continues until the MP3 Player is shut off. The continuous flow of electrons while the MP3 player is on is an electrical circuit. What do you need to make a circuit work? • A circuit needs these four components to work. – A source of electrical energy (the battery) – A load* (the light bulb) – Electrical conductors (copper wires and connectors) – A device to control the electric current (the switch**) *Load: a device that changes electrical energy into another form of energy such as heat, light or sound. ** Switch: a device in an electric circuit that controls the flow of electrons by opening (or closing) the circuit. Flashlight Diagram The batteries are the energy source, the bulb is the load, the switch controls the flow of electrons, and the connecting wires provide a closed path that joins all of the parts of the circuit together Electrical Energy • Electrical Energy – the energy provided by the flow of electrons in an electric circuit. • - We use electrical energy in our stoves, electric lights, heaters Sources of Electrical Energy There are two main sources of electrical energy: batteries & electrical generating stations Batteries Supplies small amounts of electrical energy Electrical Generating Stations Supplies large amounts of electrical energy Electric Cells • Portable devices such as cameras, cell phones, and flashlights require a portable source of electrical energy. • An electric cell is a portable device that converts chemical energy into electrical energy. What is an electric cell? • An electric cell is composed of two electrodes in a conducting solution, called an electrolyte. • One electrode can be easily positively charged and the other is negatively charged. • When the ends of the electrodes are connected by a conducting wire of a circuit, electrons can begin to flow from one electrode to another. • Electrons in the electrolyte are repelled away from the negative electrode and are attracted to the positive electrode. Two types of electric cells: Primary Cell: an electric cell that may only be used once. • primary cells cannot be recharged because the chemical reactions that produce the flow of electrons are not reversible. • Ex. Zinc Chloride Cells, Alkaline Cells, Lithium Cells Two types of electric cells: Secondary Cell: an electric cell that can be recharged. • secondary cells are electric cells that can be recharged and used multiple times • electrical energy from the wall can be used to reverse the chemical reactions that take place in a secondary cell. • Ex. Lead-acid batteries (in cars) and nickel metal hydride (NiMH) batteries. Fuel Cells • A special type of electric cell through which a continuous supply of chemicals is pumped as the cell operates. • During this process, any waste products are removed. • Fuel cells can operate for far longer than a typical electric cell. • Ex. Fuel Cell Vehicles (FCVs) – vehicles that operate using fuel cells instead of gasoline. For more info – p. 513 Forms of Current Electricity p.515 Direct Current (DC) – a flow of electrons in one direction through an electric circuit. - Produced by an electric cell such as a battery. - Portable devices use direct current Alternating Current (AC) – a flow of electrons that alternate in direction in an electric circuit. - Wall outlets provide alternating current. - Devices such as ovens, clothes dryers, lights use alternating current. HOMEWORK • HOMEWORK: Pg 510 #4-6 Pg 514 #6 Pg 517 #2,3