1、CHAPTER 20 GLENCOE PHYSICSStatic ElectricityCHAPTER 20 GLENCOE PHYSICSStatA. Charge1. Charge - basis for electricity a. two types - “+” or “-” based on the excess or deficiency of electrons. Named by Ben Franklinb. can be created chemically, mech., etcc. like repel, unlike attractA. Charge1. Charge

2、- basis for2. Microscopic view of Chargea. Atom is neutral - electrons balanced by protons. Electrons in orbit around nucleusb. With addition of energy, electrons removed leaving a positive ion. Freed electrons become attached to other material and have a negative ion.(1) neutral objects charged by

3、rubbing(2) conservation of charge is critical2. Microscopic view of Chargea3. Conductors and Insulatorsa. Insulators - materials through which charges do not move easily. Charges removed from one area are not replaced by charges from another areab. Conductors - materials such as metals that allow ch

4、arges to move(1) Charge is carried by the movement of electrons.3. Conductors and Insulatorsa.(2) metals have an electron that can be easily removed as electrons act as though they belong to the entire whole - an electron cloud(3) Air is an insulator, but under certain conditions sparks can occur.(2

5、) metals have an electron th4. Concentration of Chargea. charged body distributes charge over the surfaceb. distributed to bring about equilibriumc. pointed surfaces have a higher concentration of charged. Grounding - same charge per unit area, removal of excess charge.4. Concentration of Chargea. c

6、B. Electric Force 1. more powerful than gravity and both attractive and repulsive2. Charging by Conduction - charging a neutral body by touching it with a charged body. Positive or negative3. Charged by induction - charge an object without touchingB. Electric Force 1. more powe3. Coulombs Lawa. 1785

7、 - Charles Coulomb devises an experiment to measure the electric force.b. “The magnitude of the force that a tiny sphere with charge q exerts on a second sphere with charge q, separated by a distance d, is given by the equation3. Coulombs Lawa. 1785 - Char(1) Force that q exerts on q and that q exer

8、ts on q(2) What concept is this analogous to?c. Hold for point charges or spherically shaped charges. Distance is between the centers of such objects.(1) Force that q exerts on q d. Unit of charge is the Coulomb (C)(1) one coulomb is the charge on 6.25 x 1018 electrons(2) lightning bolt is about 7 -

9、10 C(3) elementary charge is the charge on one electron - negative 1.60 x 10-19 Ce. For charge in Coulombs, distance in meters, and force in Newtons k = 9 x 109 N-m2/C2d. Unit of charge is the Coulof. Electric Force - a vector quantity, must show direction.(1) repulsive forces - positive signs, forc

10、e on object is away from second object.(2) attractive forces - negative signs, force on object is toward second object.g. A charged object is always attracted by a neutral object (and, by 3rd Law, a neutral object is attracted to a charged object)f. Electric Force - a vector q4. Problemsa. Two point

11、 charges of magnitude 3 x 10-9 C and 6 x 10-9 C are separated by 30 cm. Find the force of repulsion.F = (9x109)(3x10-9)(6x10-9) / .32 = 1.8 x10-6 N 4. Problemsa. Two point chargb. A 4.5 x 10 -9 C charge is located at 3.2 m from a - 2.8 x 10 -9 C charge. Find the electrostatic force.c. An electron an

12、d a proton of a hydrogen atom are separated by a distance of 5.3 x 10 -11 m. An electron has a charge of - 1.60 x 10 -19 C and a mass of 9.11 x 10 -31 kg. A proton has a mass of 1.67 x 10 -27 kg. Find the electrostatic and gravitational forces between the two. How could you find the speed of the ele

13、ctron? Find it.b. A 4.5 x 10 -9 C charge is la. F = - 1.11 x 10 -8 N Attractive b. FG = 3.6 x 10 -47 N attractiveFE = - 8.2 x 10 -8 N attractiveFc = FG + FE = m v 2 /rtherefore v = 2.18 x 10 6 m/sa. 5. Principle of Superpositiona. When two or more charges affect a different charge, the resultant for

14、ce acting on the charge equals the vector sum of the various individual charges present.b. A 2.2 x 10 -9 C charge is located at x = -1.5m, a 5.4 x 10 -9 C is located at x = 2 m, and a 3.5 x 10 -9 C charge is located at the origin. Find the net force acting on the charge at the origin.5. Principle of Superpositiona F 3-2 = 3.08 x 10 -8 NF 3-1 = 4.25 x 10 -8 N Fnet = F 3-1 - F 3-2 = 1.17 x 10 -8 N towards q2+q1 1.5 q32 m q2F3-2