Physics II- Ch 19 notes
Physics II- Ch 19 notes 1012
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This 4 page Class Notes was uploaded by ShayD on Sunday January 31, 2016. The Class Notes belongs to 1012 at University of Missouri - St. Louis taught by David Hornes in Spring 2016. Since its upload, it has received 56 views. For similar materials see Basic Physics II in Physics 2 at University of Missouri - St. Louis.
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Date Created: 01/31/16
Dudaie 1 Physics II: Chapter 19 Electric charges, Forces, and Fields “Like attracts like” 1. Electric charge a. There are 2 types of charges on any given objects i. Negative () = electron 1. All electrons have some defining intrinsi19roperties a. electric charge e= 1.60 x 10 C b. mass M =e9.11 x 10 kg31 ii. Positive (+) = proton 19 1. electric charge e= 1.602710 C 2. mass M =p1.673 x 10 kg iii. Object with equal amounts of both charges have a zero net charge Neutral b. Conservation of electric charge i. The total electric charge of the universe is constant, no physical process can increase of decrease in the total amount of the electric charge in the universe; electric charge can only be transferred c. Polarization i. The ability of charged objects to attract small neutral objects 1. When a positively charged object is held near a neutral object the opposite charges are attracted to the charged particles while the opposite charges are repelled a. This causes an induced polarization which leads to an attractions Dudaie 2 2. Coulomb’s Law F=k |q1 |q2 | 9 a. r2 ; k= 8.99 x 10 i. He proposes that an idealized point charge q1 is separated by distance r from another point charge q . 2 ii. If both charges are at rest, the system is electrostatic b. Compare to Newton’s law of gravity i. In both cases the force decreases as the square distance between the 2 objects ii. Both depend on their intrinsic values 1. Gravity depends on the object’s masses 2. Electric forces depend on their charge iii. Coulomb force has an inversesquare dependence on distance 1. The reason gravity dominates astronomy is because electric forces cancel for neutral objects c. Types of problems i. Net force the vector sum of the forces individually in a this is called superposition 1. Individual forces on a linear path example 192 2. Individual forces no on the same line example 193 ii. Spherical charge distribution 1. Charge per area on the sphere a. Surface area density, σ. i. Q= σA active example 192 3. The Electric Field example 195 F a. E= q0 i. Electric field is the force per charge at a given location 1. F electric force 2. q 0 test charge b. electric field of a point charge |q1||q2 | i. F=k 2 r 1. If q is positive the field points radiate outwards 2. If q is negative the field is radially inwards Dudaie 3 4. Electric Field Lines a. When a system of equal and opposite charges are separated by a nonzero distance, is known as an electric dipole b. electric field lines contact the conductor at right angles c. Parallelplate capacitor i. 2 conducting plates with opposite charges are placed parallel to each other example 196 ii. Excess charge whether positive or negative moves the the exterior surface of the conductor 5. Electric Flux a. The electric field “flows,” through an area i. You can calculate it via Φ=EA 1. When the object is parallel to the electric field Φ=0 ii. Dudaie 4 6. Gauss’s Law a. The electric field on the surface of the sphere has a constant magnitude E=k q i. (r2 ii. Since electric field is everywhere perpendicular to the spherical surface q 2 1. ϕ=EA= k( ))2 (Πr =)Πkq r a. From this we can derive a new constant permittivity of free space ε0= 1 =8.85x10 −12 b. 4πk b. If the charge q is enclosed by an arbitrary surface, the total electric flux through the surface Φ i. Φ= q/ ε0 c. Gaus sian surface i. A Gaussian surface is a closed surface in threedimensional space through which the flux of a vector field is calculated; usually the gravitational field, the electric field, or magnetic field.
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