Electric Forces & Fields. Electric Forces & Fields. Charge. Charging an Object-by Contact. Charging an Object-by Induction 5/1/2017.

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1 5/1/017 Electic Foces & Fields Electic Foces & Fields Eyes Chage Eyes Activity to Do Take two 9inchlg pieces of tanspaent tape and place them sticky side down a plastic, glass, o wooden tabletop. Now pull e end of each tape to emove them fom the table. Bing the pieces of tape nea each othe. They epel each othe, as shown in the figue. Can we explain the epulsi of the tapes as an electic inteacti? Now place e piece of tape top of anothe sticky side down the table. Pull them both up. Then pull them apat and obseve thei inteactis. Chage Quantized: multiple of a fundamental unit of chage, e The SI unit of chage is the coulomb ( e = 1.6 x C Positive: pot chage e Negative: elect chage e Foces between objects Repel (Like chages) Attact (Unlike chages) Neutal objects: chage sepaati Exceptis: see fundamental paticle chat Chaging an Objectby Ctact Chaging an Objectby Inducti Ctact A chaged object (od) is placed in ctact with a neutal object (sphee) Some elects the od move to the sphee When the od is emoved, the sphee is left with a chage The object being chaged with same type chage as od A negatively chaged ubbe od is bought nea an unchaged sphee The chages in the sphee ae edistibuted A gounded cducting wie is cnected to the sphee The wie to gound is emoved, the sphee is left with excess positive chage The positive chage evenly distibutes 1

2 5/1/017 Cductos & Insulatos Cducto: In metals, some elects can move feely thoughout the metal. Insulatos: Plastic, glass, and othe nmetal mateials do not have fee elects o any othe chaged paticles that ae fee to move inside. Also called Dialectic Polaizati Net chage Iizati Electic dipole Hydogen bd Watch fo these tems 014 Peas Educati, Inc. Ou New Foce List Electic Foces & Fields Electic Foce Eyes NCtact: Lg Range Foces Gavitatial Foce (Weight) Electic Foce Ctact Foces Tensi Foce Nomal Foce Ficti Foce Sping Foce Buoyancy Foce Coulomb s Law q is chage is distance between centes k is a cstant Electic Foce F1 = 57 degees E of N 116 degees Vecto Review Add vectos by compents 35 cos(33)= cos(64)= sin(33)= sin(64)= k e q 1 q F 1 F = _87 deg below x axis_

3 5/1/017 Find the Electic Foce a Chage Find Fe Supepositi of Foces Remembe how to add vectos Use tabula fom Find the Electic Foce q1 caused by the q and. q1= q = 4 µc = 3 µc q1 q N C q1 4 m 3m q R1= R13=8m 6 m Finish the poblem Finish the poblem F 1 by degees W of N Negative 5.75x10 3 sin 37º= F 1 by 90 degees F 1 by and 3 Positive 5.75x10 3 cos 37º= F 1 degees W of N C Negative 5.75x10 3 sin 37º= 3.46x10 3 Positive 5.75x10 3 cos 37º= 4.6x10 3 F 1 by 90 degees Zeo Negative 1.69x10 3 (3x10 C 3.46x x10 3 F 1 by and 3 = 4.5x º above x axis Electic Field Electic Foces & Fields Electic Field Eyes Foce pe Unit test chage: A Ratio F E = Fom Coulomb s Law q0byq q0 kqq E = q 0 0 kq E = 3

4 5/1/017 The Field Model The Field Model We define the electic field Eat the point (x, y, z) as The units ae newts/coulomb, N/C. The magnitude Eof the electic field is called the electic field stength. 015 Peas Educati, Inc. 015 Peas Educati, Inc. The Field Model Compaing Fields The field model descibes how chages inteact: 1. A goup of chages, which we will call the souce chages, altes the space aound them by ceating an electic field E.. If anothe chage is then placed in this electic field, it expeiences a foce Fexeted by the field. Electic Fields kqbyq kqby q Eq Gavitatial Fields Gmbym Gmby m gm 015 Peas Educati, Inc. Find Electic Field at a Point Find Ee Find the Electic Field at locati pcaused by the q and. q = 4 µc = 3 µc p q N E = C q1 4 m 3m q R1= R13=8m E = C 6 m 4

5 5/1/017 Finish the poblem E at 1 degees W of N E = C E at 1 by 90 degees (3x10 E = C E at 1 by and 3 = Electic Foces & Fields Electic Field Lines Eyes Electic Field Lines Electic Field Lines 015 Peas Educati, Inc. 015 Peas Educati, Inc. Electic Field Lines Electic Field Lines Field lines cannot coss. The tangent to the field line is the electic field vecto, which indicates the diecti. The electic field is ceated by chages. Field lines stat a positive chage and end a negative chage. Spacing indicates stength 015 Peas Educati, Inc. 015 Peas Educati, Inc. 5

6 5/1/017 Find Positively chaged objects Negatively chaged objects Weak Efields Stg Efields Cstant Efield aea Inteactives Aluminum Can Polaizat Name that Chage Simulatis Phet.Coloado.edu Ballos and Static electicity Chages and Fields (used in lab 6) Foces and Toques in an Electic Field Afte time, the fagments sot into distinct lines, ceating a genetic fingepint. Two identical DNA samples would poduce the same fagments and theefoe the same patten. It is extemely unlikely that two unelated DNA samples would poduce the same patten. 015 Peas Educati, Inc. Example Poblem An electic field E= (00,000 N/C, ight) causes the.0 g ball to hang at an angle. What is θ? Example Poblem What is the magnitude and diecti of the electic foce chage A? 015 Peas Educati, Inc. 015 Peas Educati, Inc. 6