Electrostatics (aka Static Electricity )

Transcription

1 Electrostatics (aka Static Electricity )

2 What is Electrostatics? Electrostatics is the study of the behavior of stationary charged objects.

3 It s all about the electrons (in constant, random motion around the nucleus) and protons (stuck in the nucleus) Negative Electron Nucleus: positive protons & neutral neutrons

4 The Atom & its particles Electrons are negatively charged particles moving around the nucleus (in orbitals) electron = e- Protons are positively charged particles located inside the nucleus (w/the neutral neutrons) proton = p+ Electrons are able to be stripped off an atom (friction: fur & pvc pipe) Protons are NOT able to leave an atom because they re stuck in the nucleus!

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6 Types of Materials 1. Conductor: a material that transfers charge easily (ex. Metals: gold, silver, copper). 2. Insulator: a material that does not transfer charge easily (ex. Plastics, glass, cork) 3. Semiconductors: somewhere between 1 & 2 (ex. Silicon, carbon, germanium). 4. Superconductors: some metals become perfect conductors below certain temperatures 5. Train Conductor: a person who drives a train.

7 Law of Conservation of Electrical Charge Electrons may be transferred from one object to another, but they will never disappear or appear from nowhere. Electron abundant = negative charge Electron deficient = positive charge

8 Electrically charged objects... Exert a force on each other Unlike charges attract Like charges repel

9 There are four methods to charge an object:

10 1. Charging by Friction using friction to remove electrons from one object and placing them on the other object. Result: two objects with opposite charge Walk across carpeted floor with wool socks and you can build up an excess of charge (either on you or the carpet) and therefore, become charged. Fur becomes positively charged. Why? Rod becomes negatively charged. Why? Can use friction to remove electrons from fur and deposit onto rod.

11 2. Charging by Contact (or Conduction) The process of giving one object a net electric charge by placing it in contact w/another object that is already charged is known as charging by contact. Result: two objects with same charge

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13 3. Temporarily Charging by Induction An object may become polarized (opposite ends) while a charged object is brought near. But, the overall charge on this piece of plastic (for example) is neutral. Result: two objects with opposite charge temporarily When the charged rod goes away, the electrons rearrange and disperse evenly. Object is still neutral.

14 4. Permanently Charging by Induction The process of giving one object a net electric charge without touching the object to a second charged object is called charging by induction.

15 Permanently Charging by Induction Polarization

16 5. Credit Card Charging: You may use Visa, Master Card, or American Express Result: Debt from high interest rates!

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19 Check out these animations! hp?sim=john_travoltage hp?sim=balloons_and_static_electricity

20 Van de Graaf Generator

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22 Electric Fields What is an electric field? A region of space where a charge exerts a force on other charged objects. This field extends outward and permeates all of space. Direction of Electric Field = Direction of Force the field produces on a positive charge in the field. In comparison: What is a gravitational field? How to measure an electric field: Using a SMALL POSITIVE test charge, move it around a charged object (that is creating an Electric Field) and the magnitude and direction of force acting on the small positive test charge is measured. The strength of the field is measured based on the force on the test charge.

23 E F.. on.. q q E F = The force felt by (acting on) the test charge, q, due to the point charge s electric field. (N) q = the charge of the test charge. (C) E = Electric Field Strength. (N/C) (Direction is based on imagining a small positive charge in the field.) The Electric Field (E) at a given spot can exert a variety of forces, depending on the magnitude of the test charge placed there. F q E = F/q = F/q = F/q E is constant for that particular point charge at a given location (the Point Charge is the charge whose field is being tested the point charge is creating the Electric Field. )

24 Compare Compare the electric field equation to the one we used to measure Earth s gravitational field strength: a F m E So, Electric Fields are measured in N/C and are a measure of the force felt by a small positive test charge. (The test charge must be small in charge so that we can ignore its electric field.) F q

25 Electric fields: Man holding point charge, girl holding test charge.

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28 Must click on 2 nd link! hp?sim=electric_field_hockey p?sim=charges_and_fields p?sim=electric_field_of_dreams