Electricity Do your clothes stick together when you
- Slides: 47
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?
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 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.
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
Triboelectric Series
Electroscope No Chargeleaves 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. . . - - - - The attraction between the rod attraction and + charge is greater than the repulsion between the rod and - charge. –––– ++ + + paper Electrons are repelled. 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 induced charges - - - ++ + metal can - - -
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 / time • P = VI J/s watts W
Electricity • Safety – Fuse – Circuit breaker – Gfi – Read 20. 3
- Electric force clothes sticking together
- Static electricity and current electricity
- Current electricity
- How are static electricity and current electricity alike
- What is unity and coherence
- Two football players collide and stick together
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