Chapter_26_lect_pls - Rayleigh criterion Chapter 26...

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Chapter 26 Electric Charges and Forces Rayleigh criterion
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Properties of Charge two kinds of charge positive (+) and negative ( ) charged objects have one charge in excess neutral object have equal numbers of + and – charges. charged objects can polarize a neutral object creating an induced dipole . dipole. A neutral object which is polarized (has some degree of charge separation). like charges repel opposite charges attract the force between charges decreases with increasing separation charged objects attract neutral objects the variable used for charge is q SI unit of charge is the Coulomb (C). 1 C = 1 A s (1 Coulomb = 1 Ampere second) charge is quantized in units of fundamental charge e = 1.60 ×10 19 C (electron charge = e ; proton charge = + e )
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Conductors and Insulators Material objects can be roughly divided into two classes. Conductors Charge moves freely through the conductors. Metals are the classic example. While the electrons bound to the metal, they form a sea of electrons that can move freely. Excess charge resides only on the surface of conductors. Insulators Charge is tightly bound to the individual component atoms and molecules and cannot move through the insulator. Excess charge can reside throughout the bulk of the material. However in practice most charging methods only charge the surface. Moisture on the surface of some insulators can provide a small conductivity permitting charges to migrate.
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Triboelectric Series Most positively charged + Air Human skin Leather Rabbit's fur Glass Quartz Mica Human hair Nylon Wool Lead Cat's fur Silk Aluminium Paper ( Small positive charge ) Cotton ( No charge ) 0 Steel ( No charge ) Wood ( Small negative charge ) Lucite Amber Sealing wax Acrylic Polystyrene Rubber balloon Resins Hard rubber Nickel, Copper Sulfur Brass, Silver Gold, Platinum Acetate, Rayon Synthetic rubber Polyester Styrene (Styrofoam) Orlon Plastic wrap Polyurethane Polyethylene (like Scotch tape) Polypropylene Vinyl (PVC) Silicon Teflon Silicone rubber Ebonite Most negatively charged Source: Wikipedia, accessed 2011 Jan 20 When two materials are rubbed together, the material higher on the list acquires the positive charge, while the lower material, the negative charge.
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Charging by Electrostatic Induction A charged rod will charge a neutral sphere with the opposite charge. This is a step-wise process. Polarize sphere with initial charged rod. Ground sphere. Break ground Withdraw charged rod This works because the charged rod changes the potential of the neutral sphere. We will talk more about this later in the course. What is going on? C harge (q) has absolute meaning. Potential (V) is relative. http://www.physicsclassroom.com/
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Charging by Electrostatic Induction http://www.physicsclassroom.com/ 1 charged rod 2 electrically connected spheres Polarize sphere with initial charged rod.
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Chapter_26_lect_pls - Rayleigh criterion Chapter 26...

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