Quiz 1

Physics 7C SS1 Lecture 2: Wave Model Total Phase… and Implications for Interference

Agenda Review Simple Harmonic Wave model Introduce total phase Graphing practice (briefly) Introduce total phase Phase chart representation Introduce interference Causes of interference types Lots of waves: good thing is once we know the wave model, we can apply it to any situation with a wave.

  The Total Phase Making sense of the wave equation: Using Total Phase Charts: 2π  2π   Unit circle Wave 1

Total Phase Which of the following includes only points with a total phase of exactly /2? A) All B) ABC C) ADG D) AEH E) ACF

Total Phase Which of the following includes only points with a total phase equivalent to /2? A) All B) ABC C) ADG D) AEH E) ACF

Fixed Phase Constant Which of the following lists only points with a fixed phase constant of exactly to /2? A) All (The wave paramaters apply at all peaks. They share the same amplitude, equilibrium, wavelength, period, and fixed phase constant) B) ABC (These were all at t=0 s for different positions) C) ADG (These were all at x=0 m for different times) D) AEH (These were all at peaks--quite likely the same peak that had traveled, and thus =/2) E) ACF (These were all at peaks, though at least A and C were different peaks.  at each is equivalent to /2)

  The Total Phase Making sense of the wave equation: Using Total Phase Charts: 2π  2π   Unit circle Wave 1

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

A vibrating object acts as the source of the wave A vibrating object acts as the source of the wave. As a speaker moves through a cycle, it fixes the period and frequency. A = Amplitude, controlled by what starts the wave T = Period, how long to get back to where it started  = Wavelength, repeat distance in space T = where f is the frequency Velocity v = 

Interfering Sound Waves What type of interference would result? Constructive Destructive Partial No interference

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

Interfering Sound Waves + Greater pressure fluctuations More & less intense means louder and softer Amplitude is zero

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

What factors might influence type of interference? 2π  2π   Unit circle Wave 1 Wave 2 Difference Anything that helps determine total phase!!!

What is responsible for the destructive interference in this case? x=0 x=/2 x  None of the above

What is responsible for the destructive interference in this case? x=0 x=/2 x  None of the above (and other terms like =0)

Interference for differing frequencies: Beats. 1 2 3 4 5 What type of interference occurs at each point?

Wavefront Representation

Wavefront Representation How long is the marked distance? /2  T/2 T