Electrostatics(Elecro-magnetic field)
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1. Electrostatics describes static electricity and the forces between electric charges at rest. 2. Electric charge is a fundamental property that comes in discrete quantities and is conserved, meaning it can be transferred but not created or destroyed. 3. There are several ways charges can be transferred, including through friction, conduction, or induction. Rubbing materials like silk and glass leads to a transfer of electrons that leaves one material positively charged and the other negatively charged.
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Electrostatics(Elecro-magnetic field)
- 2. Electrostatics GIRL SAFELY CHARGED TO SEVERAL HUNDRED THOUSAND VOLTS GIRL IN GREAT DANGER AT SEVERAL THOUSAND VOLTS
- 3. Electrostatic Charges A New Fundamental Physics Quantity The charge of an electron (qe) is -1.6 x 10-19 C The SI unit for charge is called the coulomb (C). Common electrostatic charges are small: millicoulomb = mC = 10-3 C microcoulomb = µC = 10-6 C nanocoulomb = nC = 10-9 C Electrostatic charge is a fundamental quantity like length, mass, and time. The symbol for charge is q. ATTRACTION AND REPULSION The charge of an proton (qp) is 1.6 x 10-19 C
- 4. The Nature of Electric Charge The Greeks first noticed electric charged by rubbing amber with fur, then picking up bits of matter. The Greek word for amber is elektron. Charge is conserved, meaning it cannot be created or destroyed, only transferred from one location to another. Benjamin Franklin arbitrarily called the two kinds of charge positive and negative. In most cases, only the negative charge is mobile. In all atoms, electrons (qe) have negative charge and protons (qp) have positive charge. Discovery of charge Like charges repel, and unlike charges attract. Properties of charge Charge is quantized, meaning it comes in discrete amounts (like money). total charge = integer x fundamental unit of charge
- 5. Electric Charge The Transfer of Charge SILK Glass Rod Some materials attract electrons more than others.
- 6. ElEctric chargE thE transfEr of chargE silK glass rod -+ as thE glass rod is rubbEd against silK, ElEctrons arE pullEd off thE glass onto thE silK.
- 7. Electric Charge The Transfer of Charge SILK Glass Rod - -+ + Usually matter is charge neutral, because the number of electrons and protons are equal. But here the silk has an excess of electrons and the rod a deficit.
- 8. The Transfer of Charge SILK Glass Rod - + + + + + Glass and silk are insulators: charges stuck on them stay put. --- -
- 9. Electric Charge + + Two positively charged rods repel each other.
- 10. History 600 BC Greeks first discover attractive properties of amber when rubbed. 1600 AD Electric bodies repel as well as attract
- 11. Electric Forces and Electric Fields CHARLES COULOMB (1736-1806) MICHAEL FARADAY (1791-1867)
- 13. •Electric charges at rest (static electricity) •Involves electric charges, the forces between them, and their behavior in materials Electrostatic s
- 14. • Arise from the particles in atoms • Alone: Billions and billions of times as strong as the force of gravity • In Pairs: Cancel each other out and have no noticeable effect Electric Forces
- 15. Conservation of Charge •No case of the creation or destruction of net electric charge has ever been found •Electrons are always transferred in whole – they cannot be divided into fractions of electrons Electrons are never created nor destroyed, but are simply transferred from one material to another
- 16. Charging by Friction Materials have different affinities for electrons. When insulators are rubbed together, one gives up electrons and becomes positively charged, while the other gains electrons and becomes negatively charged. • plastic foodwrap that sticks to a container • sweater pulled over your head that sparks • laundry from the dryer that clings Common examples of charging by friction: A material will give up electrons to another material below it on a triboelectric series. • small shocks from a doorknob after walking on carpet with rubber-soled shoes • balloon rubbed with hair sticks that to a wall
- 17. Charging by Conduction When a charged conductor makes contact with a neutral conductor there is a transfer of charge. Electrons are transferred from the rod to the ball, leaving them both negatively charged. Electrons are transferred from the ball to the rod, leaving them both positively charged. Remember, only electrons are free to move in solids. CHARGING NEGATIVELY CHARGING POSITIVELY Notice that the original charged object loses some charge.
- 18. Charging by Induction Step 1. A charged rod is brought near an isolated conductor. The influence of the charge object polarizes the conductor but does not yet charge it. Step 2. The conductor is grounded to the Earth, allowing charge to flow out between it and the Earth. Induction uses the influence of one charged object to “coerce” charge flow.