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• Количество слайдов: 48 Static Electricity Electrical Charge: Is a concentration of electricity Unlike Charges Attract one another Like Charges Repel one another Electric Fields The effect an electric charge has on other charges in the space around it. Strength of Electric Field n n Amount of charge that produces the field And the distance from the charge Static Electricity and Charging Static electricity: is the study of the behavior of electric charges, including how charge is transferred between objects. Charges can be Transferred n Friction n Contact n Induction Charging by Friction Transferring of electrons Charging by Contact Charging by contact occurs when someone actually touches another object and the electrons are then transferred (Van de Graaf Generator) Charging By Induction A transfer of charge without contact between materials. Static Discharge Occurs when a pathway through which charges can move forms suddenly. An example would by lightning. Electric Current & Ohm’s Law Electric Current n n n The rate at which charges flows through the lamp or wires. Current: is how much electric charge flows past a pint in a circuit during a given time. Current is measured in ampes. Two Types of Current n Direct Current (DC) n Alternating Current (AC) Direct Current n n Charge flows in one direction An example would be a flashlight or most battery powered devices. Alternating Current n n Is a flow of electric charge that regularly reverses its direction. Electric current in your home and schools are like this. Conductors and Insulators n Electrical Conductor n Electrical Insulator Electrical Conductor n n Is a material through which charge can flow easily For example: copper; silver; and most metals Electrical Insulator n n A material through which a charge cannot flow through easily. For example: Wood; Plastic; rubber; and air Resistance n n n Is the opposition to the flow of charges in a material. The S. I. unit of resistance is Ohm. A materials thickness, length, and temperature affect its resistance. Superconductor n n Is a material that has almost zero resistance when it is cooled to low temperatures. The best superconductor so far is cooled to 138 K. Voltage n In order for charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy. Voltage n n Potential Difference: is the difference in electrical potential energy between two places in an electrical field. It is measured in joules per coulomb, or volts, it can also be known as voltage. Voltage Sources n Batteries n Solar Cells n Generators Voltage Sources n n n Battery: is a device that converts chemical energy to electrical energy. Have terminals that can connect to wires in a circuit. One terminal is positive and the other is negative. Ohms Law n n Founded by German Scientist Georg Ohm. First determined how resistance and current affect voltage. Discovered that voltage is not the same everywhere in a circuit. Hypothesized that resistance reduces the voltage. Ohm’s Law n n n Ohm’s Law: the voltage (V) in a circuit equals the product of the current (I) and the resistance (R). V = I x R or I = V/R Increasing the voltage increases the current. Keeping the same voltage and increasing the resistance decreases the current. Circuit Diagrams n n n Electric Circuit: A complete path through which charge can flow. Ex. Wiring in a house Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy. Circuit Diagrams n Circuit diagrams shows one or more complete paths in which a charge can flow. Series Circuits n n n Series Circuit: charge has only one path through which it can flow. Ex. Christmas Tree Lights If one element stops functioning in a series circuit, none of the elements can operate. Parallel Circuits n n Parallel Circuit: is a electric circuit with two or more paths through which charges can flow. If one element stops functioning in a parallel circuit, the rest of the elements still operate. Power & Energy Calculations n n Electric Power: the rate at which electrical energy is converted to another form of energy. The unit is Watt or joules per second Power is often measured in Kilo. Watts. Electric power can be calculated by multiplying voltage by current Power and Energy Calculations n Electric Power n P (Watts) = I (Amps) x V (volts) Electrical Energy n n E=Pxt This equation is used to find the electrical energy used by an appliance. Electrical Safety n Correct wiring, fuses, circuit breakers, insulation, and grounded plugs help make electrical energy safe to use. Home Safety n n Fuses: prevents current overload in a circuit. Circuit Breakers: is a switch that opens when current in a circuit is too high. Personal Safety n Grounding: when the electric takes a shorter path to a wire which leads to the ground. This is a transfer of excess charge through a conductor. Electronic Devices n n n Electronic Signals Vacuum Tubes Semiconductors Solid-State Components Communications Technology Electronic Signals n n Electronics: the science of using electric current to process or transmit information. Electronic Signal: is information sent as patterns in the controlled flow of electrons through a circuit. Electronic Signals n n Electronics conveys information with electrical patterns called analog and digital signals. Analog Signal: is a smoothly varying signal produced by continuously changing the voltage or current in a circuit. • Information is encoded in the strength or frequency of the analog signal. Electronic Signals n n n Digital Signal: encodes information as a string of 1’s and 0’s. Digital Signal is like Morse Code, when the current is off it produces a 0 and when it is on it produces a 1. Digital is more reliable than analog. Vacuum Tube n n Controls the flow of electrons in early electronic devices. Vacuum tubes can change alternating current into direct current, increase the strength of a signal, or turn a current on or off. Example: TV tubes Problem: burn out frequently and need replaced. They are also too large for small devices. Semiconductors n Semiconductor: is a crystalline solid that conducts current only under certain conditions. • Made with silicon or germanium • Two types of conductors n n n N-type: current flows as electrons P-type: current flows as positive charge. When the two conductors are joined electrons from the n-type are attracted to the positive p-type conductor. Solid-State Components n Most modern electronic devices are controlled by solid-state components. • Diodes • Transistors • Integrated Circuits Diode n Combines n-type conductor and ptype semiconductor. • Changes alternating current into direct current. Transistors n Has three layers of semiconductors. Current flowing through its center layer changes its resistance. • Can be used a switch, because the small current can turn another current on or off. • Can be used as an amplifier Integrated Circuits n A thin slice of silicon that contains many solid-state components. • Commonly known as chips or microchips • Used in pages, mobile phones, and computers. Communications Technology n Computer: programmable device that can store and process information. • Communication devices use microchips to make them more portable, reliable, and affordable. 