Physics 122 - LectureDate: 02/08/16

Questions?

Announcements/Reminders

Written HW #03 – Due Friday, February 12

MP HW #03 – Due Friday, February 12, by 11:59 pm.

Reading assignment (check website) – Due on 02/10/16.

Last class:

* Standing waves.

* Normal modes (resonant frequencies). - in open-open air columns. - in open-closed air columns.

* Interference

Today:

* Interference of waves (sound and light).

* Huygens's Principle (ch.34)

* Diffraction.

Frequency range for

Visible light: 4 x 10 Hz – 7.5 x 10 Hz. Hearing sound: 20 Hz – 20 x 10 Hz.

Intensity hearing range:

Sound level

Interference of waves

Interference of waves

Interference of waves

Interference of waves

Interference of waves

Interference of waves

Two in-phase sources emit

sound waves of equal

wavelength and intensity. At the

position of the dot,

A. The interference is constructive.

B. The interference is destructive.

C. The interference is somewhere between constructive and destructive.

D. There’s not enough information to tell about the interference.

Question

Slide 21-107

Question

Slide 21-108

Two in-phase sources emit

sound waves of equal

wavelength and intensity. At the

position of the dot,

A. The interference is constructive.

B. The interference is destructive.

C. The interference is somewhere between constructive and destructive.

D. There’s not enough information to tell about the interference.

Example

Two loudspeakers in a plane are 2.0 m apart and in phase with eachother. Both emit 700 Hz sound waves into a room where the speed of sound is 341 m/s. A listener stands 5.0 m in front of the speakers and 2.0 m to one side of the center. Is the interference at this point maximum constructive, perfect destructive or something else? How would the situation differ if the loudspeakers were out of phase?

Example (cont'd)