Electricity & Magnetism Part I Static Electricity
Unit 10 Concept Map Electricity and Magnetism Static ElectricityCurrent ElectricityMagnetism & Electromagnetism
The Electrical Charge Carrier The Electron –Negatively charged –9.11x kg The Proton –Positively charged –1.67x kg Why is the electron principally responsible in determining electric charge?
Charge Basics Opposite charges attract Like charges repel Electrons and protons have equal and opposite charges Lowest possible charge is that of electron or proton (no fractional charges…yet)
Benjamin Franklin Famous kite experiment First to give charges the names positive and negative First to realize Law of Conservation of Charge Invented the lightning rod
The SI Unit of Charge The Coulomb (C) 6.25x10 18 electrons (or protons) are needed to make one Coulomb The charge on one single electron/proton 1.6x C See reference table for values
Charles-Augustin de Coulomb
Questions? How does an object become negatively charged? How does an object become positively charged? What is the net charge in Coulombs of 5 electrons? What is the number of protons that make up a charge of 10 nanoCoulombs?
Law of Conservation of Charge Electric charge can neither be created nor destroyed
Transferring Charge
The Electroscope A device used to detect electric charge
Charging by Induction Isolating charge without physical contact between objects Once charged rod is removed, the electroscope stays neutrally charged
Charging by Conduction Isolating electric charge by physical contact Once rod is removed, the electroscope remains charged
Permanently Charging by Induction
Coulomb’s Law There exists an electrostatic force between charged objects that is directly proportional to the magnitude of the charges and indirectly proportional to the square of the distance between them. There exists an electrostatic force between charged objects that is directly proportional to the magnitude of the charges and indirectly proportional to the square of the distance between them. This is another Inverse-Square law This is another Inverse-Square law This force could be attractive or repulsive This force could be attractive or repulsive
Coulomb’s Law F 21 indicates force on q 1 due to q 2 F 12 indicates force on q 2 due to q 1
Coulomb’s Law
Coulomb’s Constant
Let’s Try a Problem F 21 indicates force on q 1 due to q 2
The Van de Graaff Generator Generates large static charges that build up on dome Some generators can charge to thousands of volts They are generally safe, but caution should be heeded
Electric Fields An electric field is an invisible force field that affects electric charges The field is defined based on how it affects a positive test-charge All charged objects are assumed to have an electric field associated with them
Electric Field Mapping
Electric Field Around a Positively Charged Object
Electric Field Around Charged Pairs
Electric Field of a Set of Parallel Plates
Electric Field Mapping Rules E-Field lines must never touch or cross themselves or other field lines E-Field lines run out of a positive charge and into a negative charge E-Field lines must intersect charged object at right angle (90 o ) Number and density of lines indicate field strength or intensity
Electric Field Intensity Units of electric field intensity are Newtons per Coulomb q represents charge on test-charge
Electric Field Equation for Point Charges Capital Q indicates charge on the object
Electric Potential Energy Electric potential energy is the energy stored within an electric field The work done in moving a charge within an electric field is equal to the potential energy stored The kinetic energy gained by a charged particle within an electric field is equal to the potential energy lost What are the units for EPE?
Work-Energy Theorem Review
Electric Potential Electric potential is the ratio of the work done on a charged particle within an electric field divided by the particle’s charge Units are Joules per Coulomb Other terms used for electric potential are electric potential difference and voltage
Electric Potential Units of Electric Potential are Joules per Coulomb or Volts
Electric Fields Within a Charged Object
Potential Inside a Conductor
Electric Field of a Set of Parallel Plates
The Capacitor Capacitor Uses –Frequency tuner –Power supplies –Filter –Block DC current
Capacitance of Parallel Plates
Capacitance (in terms of Charge and Voltage)
Millikan Oil Drop Experiment
E & M Part 2 Current Electricity Current Resistance Voltage Ohm’s Law Power Circuits –Series –Parallel
Electric Current Time rate of flow of electric charge I represents electric current Units of current are Coulombs per second
Electrical Resistance The opposition to steady electric current flow The unit of resistance is the Ohm ( Similar to friction there is no such thing as zero resistance Carbon Resistor
Resistance in Electrical Conductors i.e. wires Resistance depends on: –Length of wire –Thickness of wire –Type of material used (metal) –Temperature –How do you think each one of these parameters effects resistance?
Resistance in Electrical Conductors R is resistance L is wire length A is cross-sectional area is resistivity of conductor
Resistance of Electrical Conductors Wire Gauges Area Length
Resistivity Table
The Simple Circuit Needed for circuit –Voltage source –Complete path –Load
Electrical Circuit Analogy Battery Light Bulb
Schematic Symbols
Electron-Flow Current
Series Circuit Circuit that has only one path for current to flow.
Series Circuit Analogy Battery
Series Circuit Schematic
Series Circuit Equations
Parallel Circuit Circuit that has more than one path for current to flow.
Parallel Circuit Analogy Battery
Parallel Circuit Schematic
Parallel Circuit Equations
Kirchoff’s Law of Current The current going into a junction (node) is equal to the current coming out ???????? Which one of these is correct?
Electrical Safety Never Intentionally take a shock!
Electrical Safety Remove Jewelry, watches, rings, etc.
Electrical Safety Use one hand (if possible) on live circuit
Electrical Safety Strictly follow lab instructions
Electrical Safety Absolutely NO HORSING AROUND!!!
Electrical Safety Remember: Current KILLS, not Voltage –5–5 mA = ASensation felt –1–15 mA = APainful –2–20 mA = ALoss of muscle control –1–100 mA = AHeart fibrillation –2–200 mA = ASevere burns, Death
Resistor Color Code