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Sec. 20.1, Electric Charge & Static Electricity Electric Charge Electric charge is a property that causes sub atomic particles like protons and electrons to attract or repel each other. There are two types of electric charge. A positive charge, like protons have. This A produces a positively charged cation. negative charge, like electrons have. This produces a negatively charged anion. Sec. 20.1, Electric Charge & Static Electricity Electric An charge (Continued) excess or shortage of electrons produces a positive or negative net electric charge. An atom in its ground state has an overall net charge of 0. If it gains excess electrons, its net charge becomes negative If it loses electrons, its net charge becomes positive. The Coulomb (C) is the SI unit for electric charge Sec. 20.1, Electric Charge & Static Electricity Electric Like Forces charges repel Two particles that are both positively charged, or both negatively charged will repel (push away) from each other. Opposite charges attract Two particles with opposite charges (one positive and one negative will attract each other. Sec. 20.1, Electric Charge & Static Electricity Electric Electric Forces (continued) force is the force of attraction or repulsion between charged objects. Charles-Augustin de Coulomb (1736-1806) is credited with pioneering research in electric forces. Electric forces obey a law similar to that of the law of universal gravitation. Sec. 20.1, Electric Charge & Static Electricity Electric Forces (continued) The electric force on two objects is directly proportional to the net charge on each object. In other words, the greater the net charge, the stronger the attraction. The electric force on two objects is inversely proportional to the distance between the objects. In other words, the greater the distance between two charged objects. The weaker the electric force. Sec. 20.1, Electric Charge & Static Electricity Electric As Forces (continued) the distance between two charged particles is doubled. The electric force between them becomes one fourth as strong. Sec. 20.1, Electric Charge & Static Electricity Electric An Fields electric field is the effect that an electric charge has on other charges around it in space. The strength of an electric field depends on the amount of charge that produces the field and the distance from the charge. An electric field exerts an electric force on any object placed in the field. What determines the strength of the field? Notice the fields created by the two charges. Whether the charge is positive or negative, the field is always strongest near the charge. Sec. 20.1, Electric Charge & Static Electricity Static Electricity and Charging Static electricity is the study of the behavior of charges and how they are transferred between objects. There are three ways a charge can be transferred. Charging by friction Charging by contact Charging by induction Three Ways To Transfer Charges Contact Friction Induction Sec. 20.1, Electric Charge & Static Electricity Static Electricity and Charging Charging by Friction Rubbing two objects together can cause charge to move from one object to the other. Rubbing a balloon on your hair causes electrons to move from your hair to the balloon because the rubber has a greater ability to attracts electrons. Walking across the carpet does the same thing. Sec. 20.1, Electric Charge & Static Electricity Charging When by Contact a body physically touches a charged object, it can acquire a charge from the charged object. When the charge is acquired, the charge from the original charged body is reduced. Sec. 20.1, Electric Charge & Static Electricity Charging by Induction Induction charging involves the charging of an object without the objects actually touching. An example of this is when you reach for a metal door knob, the electrons in your finger cause the free electrons in the metal door knob to migrate away from your negatively charged hand. Notice how the electrons in the negatively charged finger cause the negative charge to move to the back of the door knob. Sec. 20.1, Electric Charge & Static Electricity Static Discharge Static discharge occurs when a pathway through which charges can move forms suddenly. Lightning is one of the most familiar examples of static discharge. A more common example is the shock you sometimes get after walking over carpet and reaching for a metal object like a door knob. Mt. Arenal near Liberia, Costa Rica Notice the lightning strikes produced by the ionized particles created in the Section 20.1 Quiz 1. Protons Carry a ________ charge and electrons carry a ________charge. 2. When you increase the distance between two charged particles, the electric force between them is _________. 3. The effect an electric charge has on other objects around it in space is called a/an _______ ________. Section 20.1 Quiz 4. The two things that determine electric field strength are? 5. The three ways to transfer static electric charges are ___________, ____________, and ___________. Sec. 20.2, Electric Current & Ohm’s Law Electric Current Electric current is a continuous flow of electric charge. Direct current and alternating current are the two types of current. The SI unit for current is the ampere or amp, symbolized by the letter A. Sec. 20.2, Electric Current & Ohm’s Law Electric Direct Current (continued) Current This current only flows in one direction. It is symbolized by the letters DC. This current is mostly produced by some sort of battery, such as a flashlight or car battery. Sec. 20.2, Electric Current & Ohm’s Law Electric Current (continued) Alternating Current Alternating current is a flow of current that regularly reverses direction. Most household wiring and wiring in commercial buildings is to accommodate alternating current. Sec. 20.2, Electric Current & Ohm’s Law Conductors Electrical and Insulators. Conductors mostly metals like copper, aluminum, silver, etc. are used as a pathway in which current can move. Electrical insulators (usually non-metal) is a coating around a wire that does not conduct electricity. This keeps the current on the pathway where it is needed and prevents short circuits. Sec. 20.2, Electric Current & Ohm’s Law Resistance Resistance is the opposition to flow of charges in a material. The SI unit for resistance is the ohm (Ω). Three things affect the resistance of a material. The material’s thickness The material’s length The temperature of the material Sec. 20.2, Electric Current & Ohm’s Law Resistance As (continued) electrons move through a wire, thermal energy (heat) is produced as electrons collide with other electrons and ions in the wire. As heat builds up in a conductor, its resistance increases and its conductivity decreases. Sec. 20.2, Electric Current & Ohm’s Law Resistance Because (continued) of problems with resistance it is important to choose the correct conductor material and size for each application. Superconductors Usually used in specialized applications It is a material that has almost no resistance when cooled down to low temperatures. Sec. 20.2, Electric Current & Ohm’s Law Voltage In order for charge to flow in a conducting wire, the wire must be connected to a complete loop that includes a source of electrical energy. Charges flow from areas of high potential energy to areas of lower potential energy. Potential difference is the difference in electrical potential energy between two places in an electric field. This is voltage. Sec. 20.2, Electric Current & Ohm’s Law Voltage Voltage (continued) is expressed in joules per coulomb. The three common sources of voltage are” Batteries – convert chemical energy into electrical energy. Solar cells – convert sunlight into electrical energy. Generators – convert mechanical energy into electrical energy. Sec. 20.2, Electric Current & Ohm’s Law Ohm’s Law Developed by Georg Ohm (1789-1854) Shows the relationship between voltage, current, and resistance. Expressed as V = I x R V = voltage in volts I = the product of the current in a circuit in amps R = resistance in ohms Ohm’s Law V=IR Voltage Current Volts Amps Ohms A Ω V Resistance Sec. 20.2, Electric Current & Ohm’s Law Ohm’s In Law other words, the voltage in a circuit is equal to its amperage multiplied by the resistance in the circuit. Increasing the voltage increases the current If voltage is kept constant and resistance is increased, the current (amperage) is decreased. Section 20.2 Quiz 1. A continuous flow of electric charge is called_________. 2. A flow of current that regularly reverses direction is called _______ ________. 3. A material that has almost no resistance to current when cooled to low temperatures is a ____________. Section 20.2 Quiz 4. Three common sources of voltage are ________, _________, and ________. 5. The potential difference between two places in an electric field is called _________. 6. name the three components that make up Ohm’s Law. Section 20.3, Electric Circuits Circuit Diagrams An electric circuit is a complete pathway through which energy can flow. Circuit diagrams use symbols to represent parts of circuits which include: The complete pathway Electrical energy source Devices that use the electrical energy Switches and junctions Section 20.3, Electric Circuits Types of Circuits Series Circuits In this circuit, charge has only one path. If one element stops functioning, the whole circuit shuts down Adding components to a series circuit increases resistance and decreases current, so the last component gets the least current. Section 20.3, Electric Circuits Types of Circuits Parallel Circuits Parallel circuits have two or more pathways through which the current can travel. With Parallel circuits, one element can fail and the others will continue to operate. Parallel circuits are common in homes and commercial buildings. Section 20.3, Electric Circuits Always remember that when we are talking about an electrical current, regardless of the type of circuit, it flows from high potential to low potential (positive to negative), and that the electrons flow in the direction opposite that of the current. Check page. out the diagram on the following Section 20.3, Electrical Circuits Power and Energy Calculations Electrical power is the rate at which electrical energy is converted to another form of energy. Electric power is expressed in watts (W) or the more common kilowatts (kW). The formula for calculating electric power is: P (watts) = I (amps) x V (volts) Section 20.3, Electrical Circuits Formula for Calculating Electrical Power P=IxV Power (Watts) W Current (Amperes) A Voltage (Volts) V Section 20.3, Electrical Circuits Problem: An electric oven is connected to a 240-volt line. It uses 34 amps of current. How much electrical power is used by the oven? Formula: P = I x V (Power = amps x voltage Current: 34 amps Voltage: 240 volts P = ? Watts. Plug in the numbers and do the math. Section 20.3, Electrical Circuits Problem and Energy Calculations Calculating electrical energy lets you know how much energy is used by an appliance over time. The formula for calculating electrical energy is E (electrical energy) = P (power) x t (time). Section 20.3, Electrical Circuits Formula for Electrical Energy E=PxT Electrical Energy (Kilowatt Hours) Power (Watts) Time (Hours) Section 20.3, Electrical Circuits Problem: A clothes dryer that uses 4500 watts of electrical power is operated for 3 hours. How much electrical energy has it used. Formula: E=Pxt P = 4500 watts t = 3 hours Plug in the values and do the math. How many kWh (kilowatt hours) would this be? Section 20.3, Electrical Circuits Electrical Today Safety buildings constructed in the U.S. are required to have proper wiring, grounding, fuses, insulation, and circuit breakers. Fuses and/or circuit breakers prevent circuits from being overloaded and possibly starting a fire. Insulation protects us from short circuits and electrical shock. Section 20.3, Electrical Circuits Electrical Safety (continued) Proper grounding helps to bleed off excess current and send it to ground. This can prevent electrical shock and damage to appliances Section 20.3, Quiz 1. A __________ _________ is a complete pathway through which electrical current can flow. 2. The words series and parallel are used to describe types of what? 3. Write out the formula for calculating electrical power. Section 20.3 Quiz 4. An electrical circuit which has only one pathway for current to flow is a/an ______ ______. 5. An electrical with two or more pathways for current to flow is a/an _______ _______. 6. Name 3 safety precautions that building codes require for house wiring. Section 20.4, Electrical Devices Electronic Signals Electronics is the science of using electric current to process or transmit information.\ Electronic signals are information sent as patterns in the controlled flow of electrons through a circuit. Electron flow is controlled by either altering the voltage or turning the current on and off to produce the desired signal. Electronics uses digital and analog signals to convey information with electrical patterns. Section 20.4, Electrical Devices Analog Signals Analog signals are smoothly varying signals that are produced by continuously varying the current or voltage in a circuit. Information is encoded in the strength or frequency of the analog signal. AM radio stations are an example of analog signals. Notice the smooth contours in the analog graph of a radio wave in the graph below. Section 20.4, Electrical Devices Digital Digital Signals signals encode information as a series of 1’s and 0’s. This signal is produced by pulsing the current on and off. Digital signals are more reliable than analog signals. Notice the angular shape of the graph representing digital sound. Remember, you get digital by switching current on and off. Comparison of both analog (A) and Digital (B) Section 20.4, Electrical Devices Vacuum This Tubes technology was used in early televisions, computer monitors and other viewing devices. Today, it is rapidly becoming obsolete due to plasma type devices and digital screens. Their size and the fact that they burn out frequently will soon mark the end of their usefulness. Section 20.4, Electrical Devices Semiconductors Semiconductors are crystalline solids that conduct current only under certain conditions. They are made of silicon (Si) or Germanium (Ge) Some of the purest silicon in the world comes from the Southern Pines area of N.C. Section 20.4, Electrical Devices Semiconductors In (continued) pure form, Silicon and Germanium are poor conductors, but with the addition of trace amounts of other elements to them, the current inside the crystals can be controlled. By adding trace amounts of boron to silicon, we can make a p-type (positive) semiconductor. By adding trace amounts of phosphorus to silicon, we make an n-type (negative) semiconductor Section 20.4, Electrical Devices Semiconductors By (continued) themselves, p and n type semiconductors can’t do much, but when joined together, they can be very useful in controlling the flow of electrical current. Electrons from the n-type are attracted toward the positive holes of the p-type semiconductor. The result is what looks like a positive flow of charge. Section 20.4, Electrical Devices Solid State Components Diodes are solid state components that combine 1 n-type and 1 p-type semiconductor. When voltage is applied to a diode, the current will only run from the n-type to the p-type semiconductor. This is very useful in directing current. A diode can change alternating current to direct current. Figure A is a diode made of 2 semiconductors (1 n and 1 p connected together. Diodes are two layers of semiconductors. Figure B is a transistor made of 3 semiconductors, 2 n and 1 p sandwiched together. Transistors are 3 layers of semiconductors Section 20.4, Electrical Devices Solid-State Transistors Components (continued) are solid state components with three layers of semiconductors. Transistors have two main uses. As a switch, because a small current flowing through its center layer can change its resistance and be used to switch another current on or off. As an amplifier, because a small voltage applied to one side produces a large voltage on the other. Figure A is a diode made of 2 semiconductors (1 n and 1 p connected together. Diodes are two layers of semiconductors. Figure B is a transistor made of 3 semiconductors, 2 n and 1 p sandwiched together. Diodes are 3 layers of semiconductors Section 20.4, Electrical Devices Integrated Circuits Integrated circuits, also called chips or microchips. They are a thin slice of silicon that contain many solid state components. They have allowed us to reduce the size of devices while improving their performance at the same time. Section 20.4, Electrical Devices Section 20.4 Quiz 1. The two types of electronic signals used to convey information in electric patterns are _______ and _______. 2. Crystalline solids that conduct electricity only under certain conditions are called _______. 3. N-type semiconductors carry a ______ charge, while p-type semiconductors carry a _____ charge. Section 20.4 Quiz 4. A _______ is made up of one n-type and 1 p-type semiconductor and can change alternating current to direct current. 5. A __________is made up of three layers of semiconductors, 2 n-type and 1 p-type. 6. Another name for an integrated circuit is a/an ___________. 7. What are the two main elements used in manufacturing semiconductors? Section 20.4 Quiz