Electricity Do your clothes stick together when you

Electricity • Do your clothes stick together when you take them out of the dryer? • Have your clothes ever made crackling noises when you took them off? • Have you ever gotten an electric shock from another person? • Have you ever seen sparks in your blanket at night?

Has this happened to you?

Why ? ? ? Static Electricity Static electricity occurs when there is a build up of electric charge on the surface of a material. It is called static electricity because the charges don’t move (much).

Static Electricity • Ben Franklin (and others) – Two types of electric charge – Plus and Minus names – Like repel – unlike attract – Yes the kite is real

Static Electricity How do objects acquire charge? • Charging by friction • Induced charge separation –Temporary • Charging by contact • Charging by induction

Charging by Friction When a balloon rubs a piece of wool. . . + + – – – + + wool + electrons are pulled from the wool to the balloon. Rubber has a higher electron affinity than wool The balloon becomes negatively charged and the wool positively charged

Induced Charge Separation After being rubbed, a plastic ruler can attract small bits of paper. WHY ? ? ?

Induced Charge Separation when a charged rod is close to paper scraps. . . - - - - The attraction between the rod attraction and + charge is greater than the repulsion between the rod and - charge. –––– ++ + + paper Electrons are repelled. repulsion

Charging by Conduction

Excerpt From an Electric Novel Carol put the gas pump nozzle on automatic and re-entered her car to write a check. Just then her daughter, wearing a wool sweater and nylon jacket and who's hair was standing out, reached out the window for the nozzle. Flames suddenly ignited her clothing.

What Happened? When you touch a positively charged metal ball electrons flow from the earth to the metal ball, neutralizing the charges. + + + This is called – Grounding

Charging By Induction Bring a charged rod near an object to produce induced charge separation

Charging By Induction Ground the object. Allowing electrons to flow

Charging By Induction Remove the ground, then remove the rod.

A force must be pushing the hair apart

Static Electricity • Coulomb Experiment

Static Electricity • • Force (F) is in newtons (N) Charge (Q) is in coulombs (C) Distance (R) is in meters (m) Coulomb Constant (k) 9 X 109 Nm 2/C 2

Static Electricity You and your lab partner each have a net charge of one coulomb of excess positive charge and are about one meter apart. What is the force between you? (You weigh about 500 N)

Static Electricity • How does one charge exert a force on a second charge when they do not touch? • Electric Field

Small charged grass seeds in oil between two charges.

Current Electricity • Current electricity is the rate of flow of charge. – Current (I) Ampere (A) or (C/s) • Electrons in metals • Protons, Electrons or ions in liquids and gasses • AC / DC

Current Electricity • Conductors – Insulators • Resistance (R): A material’s opposition to the flow of charges – Ohms (Ω) – Thickness, length, temperature (for metal wires)

Current Electricity • Electric Potential Difference (V): The difference in the amount of energy that a charge has between two spots in an electric field – J / C or Volt (V) – Gravity potential energy – battery

Electricity • Ohm: Was able to Relate current, resistance and potential difference for a circuit. • V = IR • Read 20. 2

Electric Circuits • Electric Circuit: a completed (closed) path that allows electricity to flow • Circuit diagram: Uses symbols to represent the parts of an electric circuit

Electricity • Series Circuit – One path • I is constant • V adds • • R adds

Electricity • Parallel Circuit – More than One path (branches) • V is constant • I adds • R goes down

Electricity • Power: how quickly the energy is transferred • P = energy / time • P = VI J/s watts W

Electricity • Safety – Fuse – Circuit breaker – Gfi – Read 20. 3