Electricity Static Rub balloon on long hair girl – Ask Why does hair stand out (force of repulsion) (charging by friction) (electron affinity) Stick balloon to wall – Ask why does it stick Induced (Temporary) charge separation Shocks from seats. Clothes from dryer. Blankets showing sparks. Why Show simulation charging balloon and sticking to wall. Electric discharge – – Show charging by conduction and induction with the good electroscope after they try in the lab The text is incorrect on p603 when it talks about charging by induction. They are describing induced charge separation

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? Electricity

Has this happened to you?

A force must be pushing the hair apart

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 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 10 9 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 500N)

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.

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

When a balloon rubs a piece of wool... Charging by Friction – 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 wool

Triboelectric Series

Electroscope No Charge- leaves hang straight down

Charging by Conduction

Contact Rod with negative charge

Contact Rod with negative charge

Contact Rod with negative charge Transfers electrons

Contact Rod with negative charge Transfers electrons Extra negative charge

Contact Rod with negative charge Transfers electrons Extra negative charge Move leaves apart.

Contact Remove rod leaves stay apart.

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 Electrons are repelled. The attraction between the rod and + charge is greater than the repulsion between the rod and - charge. paper + – + – + – + – + – + – + – + – attraction repulsion

Induced Charge Separation Rod with negative charge

Induced Charge Separation Rod with negative charge Pushes electrons in electroscope down

Induced Charge Separation Rod with negative charge Pushes electrons in electroscope down Extra negative charge

Induced Charge Separation Rod with negative charge Pushes electrons in electroscope down Extra negative charge Leaves move apart

Induced Charge Separation Remove rod everything returns

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 negatively charged rod near an object to produce induced charge separation metal can induced charges

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.

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 complete (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 / timeJ/swatts W P = VI

Electricity Safety – Fuse – Circuit breaker – Gfi – Read 20.3

4. Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells