Transformers. slide 1

Transcription

1 Transformers an alternating emf V1 through the primary coil causes an oscillating magnetic flux through the secondary coil and, hence, an induced emf V2. The induced emf of the secondary coil is delivered to the load: slide 1

2 Transformers step-up transformer, with N2 >> N1, can boost the voltage step-down transformers (N2 << N1) lower the voltage power consumed is unchanged slide 2

3 Transformers Delivering power with smaller currents at higher voltages reduces losses due to the resistance of the wires. slide 3

4 Transformers slide 4

5 HW hints Problem slide 5

6 Physics in the News The Event Horizon Telescope Collaboration held a press conference this morning, releasing the first ever black hole image. slide 6

7 Chapter 16: Electromagnetic Waves 1 Maxwell s Equations and Electromagnetic Waves 2 Plane Electromagnetic Waves 3 Energy Carried by Electromagnetic Waves 4 Momentum and Radiation Pressure 5 The Electromagnetic Spectrum slide 7

8 Electromagnetic Fields E or B? It s relative. Is there a magnetic field or not? slide 8

9 Electromagnetic Fields slide 9

10 Electromagnetic Fields slide 10

11 Electromagnetic Fields Will the charge accelerate upward? slide 11

12 Electromagnetic Fields Galilean Relativity Velocities are relative but accelerations are the same All observers (moving or not) must agree on the acceleration. slide 12

13 Electromagnetic Fields E or B? It s relative. slide 13

14 Electromagnetic Fields Do these charges repel by magnetic or electric forces? slide 14

15 Electromagnetic Fields motional emf: an electric or magnetic force? slide 15

16 Electromagnetic Fields slide 16

17 EM Field Equations The 4 fundamental equations of electromagnetism, known as Maxwell s Equations Gauss s Law for electric fields Gauss s Law for magnetic fields Faraday s Law Ampère s Law (with Maxwell s correction) The second great unification in physics. slide year old James Clerk Maxwell publishes of "A Dynamical Theory of the Electromagnetic Field" in 1865

18 EM Field Equations Gauss s Law for electric fields Charges create electric fields: slide 18

19 EM Field Equations Gauss s Law for magnetic fields There are no magnetic monopoles: slide 19

20 EM Field Equations Faraday s Law A changing magnetic field creates and electric field: slide 20

21 EM Field Equations Ampère s Law Ampère s Law is incomplete... slide 21

22 EM Field Equations Maxwell s Correction to Ampère s Law Ampère s Law is incomplete. slide 22

23 EM Field Equations Maxwell s Correction to Ampère s Law slide 23

24 EM Field Equations Ampère-Maxwell Law An electric current or a changing electric field creates a magnetic field. slide 24

25 EM Field Equations slide 25

26 EM Field Equations Ampère-Maxwell Law Symmetry in the field equations. slide 26

27 EM Field Equations Maxwell s Equations Gauss s Law Gauss s Law for magnetism Faraday s Law Ampere-Maxwell Law Lorentz Force Law slide 27

28 EM Field Equations Maxwell s Equations Differential Form Gauss s Law Gauss s Law for magnetism Faraday s Law Ampere-Maxwell Law Lorentz Force Law slide 28

29 EM Field Equations Maxwell s Equations with no Sources after some manipulation (see section 16.2) this has the form of the wave equation slide 29

30 EM Field Equations Maxwell s equations imply that the wave equation the speed of light! F/m T m/a slide 30

31 EM Field Equations Maxwell s Equations with no Sources slide 31

32 EM Waves For a plane wave, fields are constant everywhere in a plane perpendicular to direction of propagation. slide 32

33 EM Waves Field magnitudes are related: The Poynting vector gives direction of propagation: The Poynting vector has units. It gives the instantaneous power delivered by the EM wave per unit area. slide 33

34 EM Waves Wave intensity: slide 34

35 EM Waves A distance r away from a source with power Psource gives intensity slide 35

36 EM Waves Doubling wave amplitude quadruples wave energy. slide 36

37 EM Waves slide 37

38 EM Waves slide 38

39 EM Waves An oscillating electric dipole. Arrows show direction of slide 39

40 EM Waves An oscillating electric dipole. Arrows show direction of slide 40

41 EM Waves An oscillating electric dipole. slide 41

42 EM Waves Microwave ovens. slide 42

43 EM Waves Acceleration of any charge. slide 43