current electricity - chapter outline
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DESCRIPTIONCurrent Electricity - Chapter Outline. Lesson 1: Electric Current What is an Electric Circuit? Requirements of a Circuit Electric Current Lesson 2: Electrical Resistance Journey of a Typical Electron Resistance Lesson 3: Ohms Law Ohm's Law Lesson 4: Electrical Power - PowerPoint PPT Presentation
Current Electricity - Chapter OutlineLesson 1: Electric CurrentWhat is an Electric Circuit? Requirements of a Circuit Electric Current Lesson 2: Electrical ResistanceJourney of a Typical Electron Resistance Lesson 3: Ohms LawOhm's Law Lesson 4: Electrical PowerPower: Putting Charges to Work Common Misconceptions Regarding Electric Circuits Lesson 3: Circuit ConnectionsCircuit Symbols and Circuit Diagrams Two Types of Connections Series Circuits Parallel Circuits
Lesson 1: Electric Current - objectivesWhat is an Electric Circuit? Requirements of a Circuit Electric Current Power: Putting Charges to Work Common Misconceptions Regarding Electric Circuits
What is an Electric Circuit? A circuit is simply a closed loop through which charges can continuously move.
lab: light a light bulbyou are given the following material, what arrangement would result in the successful lighting of the bulb? Record all different ways your connection did not work.Record all different ways your connection did work. Write your conclusion what you must do in order for the light bulb to work.
Light Bulb Anatomy A light bulb is a device consisting of a filament attached to two wires. The wires and the filament are conducting materials which allow charge to flow through them. One wire is connected to the ribbed sides of the light bulbs. The other wire is connected to the bottom base of the light bulb. The ribbed edge and the bottom base are separated by an insulating material which prevents the direct flow of charge between the bottom base and the ribbed edge. The only pathway by which charge can make it from the ribbed edge to the bottom base or vice versa is the pathway which includes the wires and the filament.
The successful means of lighting the bulb involves placing the bottom base of the bulb on one terminal and connecting the ribbed edge to the other terminal using a wire.
The Requirement of a circuitThere must be a closed conducting loop in the external circuit which stretches from the high potential, positive terminal to the low potential, negative terminal. There must be an energy supply capable doing work on charge to move it from a low energy location to a high energy location and thus establish an electric potential difference across the two ends of the external circuit.
- exampleAs a + charge moves through the battery from D to A, it (gains, loses) potential energy and (gains, loses) electric potential. The point of highest energy within a battery is the (+, -) terminal. As a + charge moves through the external circuit from A to D, it (gains, loses) potential energy and (gains, loses) electric potential. The point of highest energy within the external circuit is closest to the (+, -) terminal.Use >,
Electric Current If the two requirements of an electric circuit are met, then charge will flow through the external circuit. This flow of charge or current, is the rate at which charge flows past a point on a circuit.Current is a rate quantity. Like velocity - the rate at which an object changes its position. Acceleration - the rate at which an object changes its velocity. And power - the rate at which work is done on an object. In every case of a rate quantity, the mathematical equation involves some quantity over time.
Electric current refers to the rate at which charge passes a given point in a circuit.
Q: the amount of charge that passes a point, in Coulombt: time, in secondsI, electric current, in ampere (A), which is a fundamental unit. 1 A = 1 C / sCurrent can only be sustained if there is difference in ELECTRICAL POTENTIAL or VOLTAGE between two points!
Andr-Marie Ampre (20 January 1775 10 June 1836) was a French physicist and mathematician who is generally regarded as one of the main discoverers of electromagnetism. The SI unit of measurement of electric current, the ampere, is named after him.
Conventional Current Direction The direction of an electric current is by convention the direction in which a positive charge would move.
Current versus Drift SpeedDrift speed refers to the average distance traveled by a charge carrier per unit of time. Current has to do with the number of coulombs of charge that pass a point in the circuit per unit of time.Even though the drift speed is extremely slow, the current could be big. This is because there are many, many charge carriers moving at once throughout the whole length of the circuit.
The Nature of Charge FlowWe know that the average drift speed of an electron is very, very slow, why does the light in a room or in a flashlight light immediately after the switched is turned on? Charge carriers in the wires of electric circuits are electrons. They are already there supplied by the atoms of the wire. Once the switch is turned to on, there is an electric potential difference established across the two ends of the external circuit. The electrons begin moving along a zigzag path in their usual direction. Thus, the flipping of the switch causes an immediate response throughout every part of the circuit, setting charge carriers everywhere in motion in the same net direction. While the actual motion of charge carriers occurs with a slow speed, the signal that informs them to start moving travels at a fraction of the speed of light.
The charge carriers never become consumed or used up. While the energy possessed by the charge may be used up, the charge carriers themselves do not disintegrate, disappear or otherwise become removed from the circuit. And there is no place in the circuit where charge carriers begin to pile up or accumulate. The rate at which charge enters the external circuit on one end is the same as the rate at which charge exits the external circuit on the other end.
Check Your UnderstandingA current is said to exist whenever _____.a wire is charged a battery is presentelectric charges are unbalancedelectric charges move in a loop
Current has a direction. By convention, current is in the direction that ___.+ charges move - electrons move+ electrons move
The drift velocity of mobile charge carriers in electric circuits is ____.very fast; less than but very close to the speed of light fast; faster than the fastest car but nowhere near the speed of lightslow; slower than Chris Rock runs the 200-metersvery slow; slower than a snail
Use the diagram to complete the following statements:A current of one ampere is a flow of charge at the rate of _______ coulomb per second.When a charge of 8 C flows past any point along a circuit in 2 seconds, the current is ________ A.If 5 C of charge flow past point A (diagram at right) in 10 seconds, then the current is _________ A.If the current at point D is 2.0 A, then _______ C of charge flow past point D in 10 seconds.If 12 C of charge flow past point A in 3 seconds, then 8 C of charge will flow past point E in ________ seconds.True or False: The current at point E is considerably less than the current at point A since charge is being used up in the light bulbs.
exampleIf charge flowing at the rate of 2.50 1016 elementary charges per second. What is the electric current?
Lesson 2: Electrical ResistanceJourney of a Typical Electron Resistance
ResistanceResistance is the hindrance to the flow of charge. For an electron, the journey from terminal to terminal is not a direct route. Rather, it is a zigzag path which results from countless collisions with fixed atoms within the conducting material. While the electric potential difference established between the two terminals encourages the movement of charge, it is resistance which discourages it. The rate at which charge flows (current) from terminal to terminal is the result of the combined affect of these two quantities: potential difference and resistance.
Variables Affecting Electrical Resistance - RThe total length of the wires will affect the amount of resistance. The longer the wire, the more resistance that there will be R is directly proportional to length. The cross-sectional area of the wires will affect the amount of resistance. The wider the wire, the less resistance that there will be to the flow of electric charge R is inversely proportional to Area. The material that a wire is made of. Some materials are better conductors than others and offer less resistance to the flow of charge. Silver is one of the best conductors but is never used in wires of household circuits due to its cost. Copper and aluminum are among the least expensive materials with suitable conducting ability to permit their use in wires of household circuits. The conducting ability of a material is resistivity. The temperature. Since resistity increases with increasing temperature, the higher the temperature, the more resistance that there will be. You can find a list of resistivity values for various materials at temperatures of 20 degrees Celsius in your reference table.
Mathematical Nature of ResistanceThe standard metric unit for resistance is the ohm, represented by the Greek letter omega - . The equation representing the dependency of the resistance (R) of a cylindrically shaped conductor (e.g., a wire) upon the variables which affect it is:
L represents the length of the wire (in meters), A represents the cross-sectional area of the wire (in m2), represents the resistivity of the material (in meter). R represents the resistance of the wire (in )
If the length of the wire is increased, Resistance is increased direct linear relationship.
If the area of the wire is increased, Resistance is decreased inverse relationship
Graph of R vs. L and R vs. A
exampleAn incandescent light bulb is supplied with a cons