Electricity

Basic Concept In Mechanics, the basic property of matter is Mass. In Electricity, the basic property is Charge.

Electrostatics Static Electricity Electric charges that are at rest

Basic Units Compare Smallest Possible Unit Practical Unit US Currency Penny $0.01 = 1/100th of a dollar Dollar $1 = 100 Pennies Electric Charge Elementary Charge (1e) electron or proton 1e = 1.6 x 10-19C Coulomb 1C = 6.25 x 1018e

Subatomic Particles Particle Proton Neutron Electron Location Relative Charge Actual Charge (C) Relative mass (u) Actual mass (kg) Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge Actual Charge (C) Relative mass (u) Actual mass (kg) Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) Relative mass (u) Actual mass (kg) Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) +1.6 x 10-19 -1.6 x 10-19 Relative mass (u) Actual mass (kg) Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) +1.6 x 10-19 -1.6 x 10-19 Relative mass (u) 1 Actual mass (kg) Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) +1.6 x 10-19 -1.6 x 10-19 Relative mass (u) 1 Actual mass (kg) 1.67 x 10-27 9.11 x 10-31 Easily detected ? Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) +1.6 x 10-19 -1.6 x 10-19 Relative mass (u) 1 Actual mass (kg) 1.67 x 10-27 9.11 x 10-31 Easily detected ? yes no Yes Easily removed?

Subatomic Particles Particle Proton Neutron Electron Location Nucleus Outside Nucleus Relative Charge +1 -1 Actual Charge (C) +1.6 x 10-19 -1.6 x 10-19 Relative mass (u) 1 Actual mass (kg) 1.67 x 10-27 9.11 x 10-31 Easily detected ? yes no Yes Easily removed? NO!!!!

Charged objects Positively charged objects have less electrons than protons Negatively charged objects have more electrons than protons Neutral objects have equal amounts of protons and electrons

Law of Charges Opposite charges attract Like charges repel Neutral objects are attracted to positive or negative objects because of polarization Polarization Separation of charges without charging object

Examples How many electrons are on a conductor if it has a charge of -4 x 10-17 C? 250 electrons What charge will 120 protons have? +1.92 x 10-17 C

Example Why is it not possible for any object to have a charge of -8 x 10-20 C? Electrons (or protons) cannot be broken down into smaller pieces.

Movement of Charge Conductors Insulators Electrons are free to move Most metals Insulators Electrons are not free to move

Movement of Charge Grounding Examples Excess charges on an object will try to move away from like charges or towards opposite charges Examples Lightning, Static electricity

Review Gravitational Force What factors affect gravitational force? Size of each mass Distance of separation

Electrostatic Force What factors will affect the amount of attraction or repulsion? Size of each charge Distance of separation

Coulomb’s Law k = Electrostatic constant, 8.99 x 109 Nm2/C2 q = charge (C) r = distance separating the center of each charge (m)

Remember Opposite charges attract Like charges repel -F means attractive force +F means repulsive force

Electric Fields Electric Field is a region around a charged object through which a force is exerted on any other charged particle. Direction of the electric field is the direction a positive charge would move if placed in the field

Electric Field Lines Lines are not real Positive  Negative Can not cross Closer lines mean stronger field

Electric Field Lines

Electric Fields Parallel Plates Electric Field is uniform between plates + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - -

Electric Field Strength, E Force per charge Amount of force felt by a charge Vector E (N/C) Fe (N) q (C)

Electric Field Strength

Work Which way will each particle be pushed by the electric field? Which way does work have to be exerted in order to move each particle against the electric field? + -

Electric Potential Difference Amount of work done per unit charge as a charged particle is moved between points A.K.A. Electric Potential Potential Difference Voltage

Electric Potential Difference V (V) W (J) q (C) 1 V = 1 J/C

Electric Potential Difference Rearranged (1C)*(1V) = 1J

Electron Volts (eV) Amount of work(energy) done by 1 volt on 1 electron Unit of Energy (1C)(1V)=1J (1e)(1V)=1eV 1eV = 1.6 x 10-19J

Why something moves Gravitational Electrical

Electrodynamics The study of charges and their motion Often use an analogy of water moving to illustrate

Flow A measure of water flow is called ____? Current How much charge flows per unit time

Current q (C) t (s) 1 Ampere (A) = 1 C/s

Current Which charge flows? Negatives (Reality) Conventional Current Positive charges (rest of the physics world) Electrons actually move

Motion What causes water to move? Change in height (Potential Difference) Water, flows from high potential to low potential

Voltage Electrical Potential difference causes charges to move. Batteries provide a Potential Difference Batteries act like a pump to raise charges from a low to high potential

Resistance Opposition to flow Any device that opposes the flow of current can be called a resistor Unit is Ohm, Ω

Ohm’s Law Potential Difference encourages charges to flow Resistance discourages charges to flow Ratio of Potential Difference to Resistance equals Current

Ohm’s Law V (V) I (A) R (Ω) 1 V = 1 A* Ω

Ohm’s Law

Resistance What factors affect the resistance of a material? Size Type of material Temperature

Resistance The size of a resistor affects the resistance Length Cross-sectional Area

Length Would water flow faster through a short pipe or a long pipe?

Length More Length increases Resistance L R

Cross-Sectional Area Would more water flow through a wide pipe or narrow pipe?

Cross-Sectional Area Larger Area decreases Resistance A R

Type of Material How does the type of material affect resistance? Electrons need to flow through the resistor. The more material that gets in the way, the slower the electrons

Resistivity, ρ Measure of how resistive a material is. As Resistivity increases Resistance Increases ρ R

All together now R (Ω) L (m) A (m2) ρ (Ω *m) Selected materials in reference tables

Temperature How would temperature affect resistivity? What does increasing the temperature do to the molecules in a resistor? Increasing Temp increases molecular movement

Temperature Imagine walking down the hall with sophomores standing every where. Imagine walking down the hall with sophomores running every where. Which is easier?

Temperature Increasing Temperature increases Resistivity Increasing Temperature increases Resistance