PHYSICS W term 2

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1 PHYSICS W tem Electicity, Magnetism, Electomagnetic Waves, Optics Pof. W. McCutcheon Henn Office hous: Monday 10:30-11:30 Fiday 10:30-11:30 o by appointment Text: Young and Feedman Univesity Physics 1 th edition, with Masteing Physics. Couse Outline: see listing at the following URL. 1

2 The coodination of the thee sections in tem will be done by Pof. Hasinoff who will teach section 00. I will be in chage of the lab. Couse website, as befoe: Maks assigned Tem 1 Midtem 1 10 Midtem 10 Assignments 10 Dec. exam 70 Suvey bonus Tem Midtem 10 Midtem 10 Assignments 10 Lab 30 Apil exam 70

3 Note: Students must pass both the witten pat of the couse, and the laboatoy component, sepaately, in ode to pass the couse. In ode to pass the witten pat of the couse, a student must obtain at least 40% in each of the Decembe and Apil examinations, and oveall 50% fo both tems. If a student achieves this, then the othe components (assignments, midtems) will be added in to obtain a total mak fo the witten pat. If the lab has been passed, then that mak will be added to obtain on oveall couse mak. Goals in tem --to have students lean the fundamentals of Electicityand Magnetism, and to put these ideas togethe to study Electomagnetism, and the poduction and popagation of electomagnetic waves. -- continue woking on solving multi-step poblems. --intoduction to the use of integal calculus in Physics, and though poblem solving, to einfoce the concepts leaned in Math. 3

4 Tutoials Tutoial sessions will continue to be held evey week, stating Jan. 1. In addition, Masteing Physics assignments will continue to be assigned. Laboatoy Expeiments will stat in week, beginning Jan. 1. All expeiments must be completed, and passed in ode to pass the lab component. Students must have a Physics laboatoy notebook (yellow softcove). This can be obtained at the bookstoe. You must have it fo you fist expeiment. Sometimes it is convenient to have a second one, but make sue that you have one fo you fist expeiment. The notes fo all expeiments will be posted on the Phys. 153 web site. Read ahead of time, and come pepaed. 4

5 Academic misconduct Students ae encouaged to wok togethe, to shae ideas, and to discuss possible solutions. But the wok handed in by each student must be his o he own wok. Plagiaism occus when a student copies fom someone else, whethe it be an assignment, o a lab epot, o an exam, and passes it off as his o he own wok. This is a seious offence, and the Univesity administation deals seveely with anyone caught engaging in this activity. 5

6 Electic chage, electic foce, electic fields Only 4 basic foces in natue. The electomagnetic foce is one of them. Basic chages Fig

7 Electic chage is conseved. The algebaic sum of all the chages in any closed system Is constant. Coulomb s Law discoveed F 1 Like chages epel, unlike chages attact. 1 q q 1 q 1 and q ae the chages in coulombs (C) F1 = kqq Fig k = Nm 9 = 8.99x10 4 πε 0 C 7

8 1 is a unit vecto to give diection to F ε0 is the pemittivity of fee space=8.85x10-1 C/N-m Chage on the electon =1.60x10-19 C (= chage of the poton) So, 1C=1/e = 6.4x10 18 electons. example 4 1 cm cube contains.4x10 electons Cu Example, fo a 100 W light bulb, 5x10 18 electons pass though the glowing filament evey sec. How do the foce of gavity and the electostatic foce compae in stength? Gmm F g 43 e.g. fo two electons = =.4x10 F kqq e 1 8

9 Why then ae we so much moe awae of the gavitational foce than we ae of the electostatic foce? Supeposition of foces Net foce on chage 1 F total F 1+ F --similaly fo chages and 3. Electic field = 13 How does each chage know of the pesence of the othe? Definition = E F q 0 q q 1 Electic field is the foce pe unit Positive test chage. q 0 (test chage) 9

10 --o stictly speaking E = lim F q0 0q (so as not to change 0 the chage distibution) Fo a point chage q and a test chage q 0, Hence 1 qq = 0 F 4πε0 q E = 4πε 0 Electic field lines can be mapped (in pinciple) with a unit positive test chage. 1 E +q -q E Unifom electic field Example of a capacito --two paallel conducting plates. 10

11 Opposite chages will be distibuted evenly on top and bottom. The E lines will then be paallel, as shown i.e. the diection of foce on a unit positive test chage. As we will see late, fo paallel plates, voltage V, and sepaation d, E=V/d. If V=500 V, d=1.0 cm, E=500/1.0x10 - =5x10 4 V/m. See example 1.7 to calculate speed, acceleation, and time to each bottom plate fo an electon eleased fom uppe plate. See example 1.8 to calculate the tajectoy of an electon eleased in a diection paalled to the plates. 11

12 Supeposition of electic fields. (a) Field of an electic dipole. +q E c =E +q +E -q -q θ c b E b =E +q +E -q + - a E +q E -q E a =E +q +E -q + An electic dipole is a combination of two chages of equal magnitude and opposite sign. Resultant electic field at each of a, b, c, is found by the supeposition of two fields e.g. at a E+ q = + πε E q 0 + q 1 q = 4πε 0 1

Physics 401. Electromagnetic Theory (Electrodynamics)

Physics 401. Electromagnetic Theory (Electrodynamics) Physics 401 Electomagnetic Theoy (Electodynamics) Please ead handouts and see couse webpages fo moe info Class: Monday, Wednesday & Fiday 9:00-10:00 Henn 302 Pofesso: Janis McKenna Office: Hennings-Physics