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