1. 1 As you enter… Pick up your quiz (sorted by section)

2. 2 Physics 7C SS1 Lecture 3: Interference The reason for studying 

3. 3 Agenda Review practice quiz Review Interference basics Review 1D interference (as studied in DLM 4) Introduce 2D interference

4. 4 Which meets the quiz requirements better? A B C: They are equally good

5. 5 Which meets the quiz requirements better? C: They are equally good B A

6. 6 What is missing from this response?

7. 7

8. 8 Quiz requirement b: method that works for a wave pulse C: They are equally good B A

9. 9 Quiz requirement b: method that works for a wave pulse C: They are equally good B A

10. 10

11. 11 Interference: When Waves Meet Phenomena: Interfering pulses on the wave machine Interfering block-wave Using Total Phase Equivalent total phase: Constructive Total phase separated by half-cycle: Destructive

12. 12 Superposition of Waves The period and wavelength are exactly the same. One wave travels to the right, one to the left.

13. 13 Interfering Sound Waves Greater pressure fluctuations More & less intense means louder and softer Greater amplitude +

14. 14 Interfering Sound Waves Amplitude is zero + No more pressure fluctuations No sound!

15. 15 Phase Chart for Interfering Waves Same rough format, but add difference (most important part!) 2π  2π  Unit circle Wave 1 Wave 2 Difference

16. 16 What is responsible for the destructive interference in this case? a)  x=0 b)  x= /2 c)  x   e) None of the above

17. 17 Introducing 2D Interference: The Ripple Tank Try to spot… Places that are very deep Places that are very shallow Places that are “normal” depth Places two crest combine Places two troughs combine Places a crest meets a trough

18. 18 d Two slits create two overlapping wave fronts Crest Trough

19. 19 d Two slits create two overlapping wave fronts Crest Trough What type of interference occurs at the marked spot? a) Constructive b) Destructive c) Partial d) Time-dependent

20. 20 d Two slits create two overlapping wave fronts Crest Trough Why? a)  x=0 b)  x= /2 c)  x  d) None of the above

21. 21 x2x2 Two slits create two overlapping wave fronts Crest Trough Why? a)  x=0 b)  x= /2 c)  x  d) None of the above x1x1 x 1 =x 2 so  x=0!

22. 22 d Two slits create two overlapping wave fronts Crest Trough What type of interference occurs at the marked spot? a) Constructive b) Destructive c) Partial d) Time-dependent

23. 23 d Two slits create two overlapping wave fronts Crest Trough Why? a)  x=0 b)  x= /2 c)  x  d) None of the above

24. 24 d Two slits create two overlapping wave fronts Crest Trough What type of interference occurs at the marked spot? a) Constructive b) Destructive c) Partial d) Time-dependent

25. 25 d Two slits create two overlapping wave fronts Crest Trough Why? a)  x=0 b)  x= /2 c)  x  d) None of the above

26. 26 d Two slits create two overlapping wave fronts Crest Trough Why? a)  x=0 b)  x= /2 c)  x  d) None of the above x2x2 x1x1 x 1 >x 2 now… x 1 =2 x 2 =1.5

27. 27 An interesting phenomenon: What are you seeing? a)Constructive Interference Only b)Destructive Interference Only c)Pathlength-dependent Interference: both constructive & destructive depending on position d)Pathlength-dependent interference: all types (const, dest, and partial) depending on position e)Partial Interference

28. 28 Laser Interference In DL you will use a shortcut to calculate pathlength difference: d sin  =  x