Your Comments. did not understand any of this wtf. so over my head I have no idea what I am doing :(

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1 You Comments Llamas, and why it is so difficult to get someone to buy me one as a pet. All ask is that it beathes fie. have simple needs people. Seiously. p.s. this lectue was had. did not undestand any of this wtf. so ove my head have no idea what am doing :( Wow! That was cool. Thee is so much that you lean in high school that you just take as factual and move on. But when you can finally see it deived and shown that it is actually tue...wow! Petty awesome. This was undoubtedly my favoite pelectue of the semeste, its so cool! was doing fine until we combined ampee's modified law and faaday's law. Also go ove the magnetic and electic fields in empty space. Ae they geneated fom the empty space itself, o do they come fom some ambient souce like stas? its mindblowing that E and mu ae elated to the speed of light. Can you calculate the speed of light moe accuately though measuing E and mu, o by measuing it diectly (with lases, etc)? suspect that people's eactions to electic and magnetic waves that ae out of phase will be quite polaized. Electicity & Magnetism Lectue, Slide

2 Physics Lectue Electicity & Magnetism Lectue, Slide

3 What We Knew Befoe Pelectue Electicity & Magnetism Lectue, Slide 3

4 Afte Pelectue : Modify Ampee s Law E Q A EA Q Q dq dt d dt D Electicity & Magnetism Lectue, Slide 4

5 Displacement Cuent eal Cuent: Chage Q passes though aea A in time t: dq dt Displacement Cuent: Electic flux though aea A changes in time D d dt E Fee space Electicity & Magnetism Lectue, Slide 5

6 Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C At time t, what is the magnetic field B at a adius (point d) in between the plates of the capacito? a d Conceptual and Stategic Analysis Chage Q ceates electic field between the plates of C Chage Q changing in time gives ise to a changing electic flux between the plates Changing electic flux gives ise to a displacement cuent D in between the plates Apply (modified) Ampee s law using D to detemine B Q Electicity & Magnetism Lectue, Slide 6

7 Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C c d a Compae the magnitudes of the B fields at points c and d. Q A) B c < B d B) B c B d C) B c > B d What is the diffeence? Apply (modified) Ampee s Law point c: (enclosed) X point d: D (enclosed) < Electicity & Magnetism Lectue, Slide 7

8 Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C d a What is the magnitude of the electic field between the plates? Q A) E B) Q Q C) D) E E Q E E Q E Q E Q Q Q E A Electicity & Magnetism Lectue, Slide 8

9 Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C d Q E a E What is the electic flux though a cicle of adius in between the plates? Q A) Q E B) E C) Q D) E Q Q E Q E E E A E Q Electicity & Magnetism Lectue, Slide 9

10 Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C d What is the displacement cuent enclosed by cicle of adius? A) B) C) D D) D D Q E D E Q d dt E D a D d dt E dq dt D Electicity & Magnetism Lectue, Slide

11 What is the magnitude of the B field at adius? Calculation Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. E Q d S a V C A) B) C) D) Electicity & Magnetism Lectue, Slide D D o d B B B B B Ampee s Law: D o d B B B

12 CheckPoint B At time t= the switch in the cicuit shown below is closed. Points A and B lie inside the capacito; A is at the cente and B is towad the oute edge. Compae the magnitudes of the magnetic fields at points A and B just afte the switch is closed A. B A < B B B. B A = B B C. B A > B B Fom the calculation we just did: B Electicity & Magnetism Lectue, Slide

13 CheckPoint a At time t= the switch in the cicuit shown below is closed. Points A and B lie inside the capacito; A is at the cente and B is towad the oute edge. Afte the switch is closed, thee will be a magnetic field at point A which is popotional to the cuent in the cicuit: A. Tue B. False B B is popotional to but At A, B!! Electicity & Magnetism Lectue, Slide 3

14 Follow-Up Switch S has been open a long time when at t, it is closed. Capacito C has cicula plates of adius. At time t t, a cuent flows in the cicuit and the capacito caies chage Q. V S C What is the time dependence of the magnetic field B at a adius between the plates of the capacito? B a (A) (B) (C) B at fixed is popotional to the cuent Close switch: V C V/ a (maximum) exponentially decays with time constant t a C Electicity & Magnetism Lectue, Slide 4

15 Follow-Up Suppose you wee able to chage a capacito with constant cuent (does not change in time). Does a B field exist in between the plates of the capacito? A) YES B) NO Constant cuent Q inceases linealy with time Theefoe E inceases linealy with time (E Q/(A ) de/dt is not zeo Displacement cuent is not zeo B is not zeo! Electicity & Magnetism Lectue, Slide 5

16 We leaned about waves in Physics Electicity & Magnetism Lectue, Slide 6

17 Electomagnetic Spectum Electicity & Magnetism Lectue, Slide 7

18 How can light move at the same velocity in any inetial fame of efeence? That's eally tippy. see PHYS 5 Electicity & Magnetism Lectue, Slide 8

19 Electicity & Magnetism Lectue, Slide 9

20 CheckPoint a An electomagnetic plane-wave is taveling in the +z diection. The illustation below shows this wave at some instant in time. Points A, B and C have the same z coodinate. E x E sin(kz - wt) Compae the magnitudes of the electic fields at points A and B A. E A < E B B. E A = E B C. E A > E B E E sin (kz - wt): E depends only on z coodinate fo constant t. z coodinate is same fo A, B, C. Electicity & Magnetism Lectue, Slide

21 CheckPoint b An electomagnetic plane-wave is taveling in the +z diection. The illustation below shows this wave at some instant in time. Points A, B and C have the same z coodinate. E x E sin(kz - wt) Compae the magnitudes of the electic fields at points A and C A. E A < E C B. E A = E C C. E A > E C E E sin (kz - wt): E depends only on z coodinate fo constant t. z coodinate is same fo A, B, C. Electicity & Magnetism Lectue, Slide

22 Clicke Question E x E sin(kz - wt) Conside a point (x,y,z) at time t when E x is negative and has its maximum value. At (x,y,z) at time t, what is B y? A) B y is positive and has its maximum value B) B y is negative and has its maximum value C) B y is zeo D) We do not have enough infomation Electicity & Magnetism Lectue, Slide