Introduction to Interference
What happens when two or more waves overlap
|
Video Instruction showmethephysics.com
This movie is part of the collection:
Prelinger
Archives Creative Commons license: Public Domain
H. Wave Front – locus of adjacent points on a wave which are in phase
Top View
Ex) Distance between arrows = .90 cm
Wavelength of wave?
λ = .30 cm
III. Periodic Wave Phenomena
Wave Interference - St. Mary's Physics 2011
St. Mary's Physics YouTube Channel
Beats
A. Interference – effect produced by two waves passing simultaneously through a region
1. Superposition – when waves overlap, the resultant displacement is the algebraic sum of the individual displacements of each wave
Monterey Institute
a) Constructive Interference
Transverse and
Longitudinal Waves
Wave Interference Student YouTube Channel St. Mary's Physics 2011
Spring
Wave -
"Show me
the Physics"
1)
2)
Amplitude?
2A
3)
Waves reemerge as separate waves
b) Destructive Interference
1.
2.
At moment of overlap, amplitudes cancel
3. Waves reemerge as separate waves
(1) vibrate up and down (2) vibrate left and right (3) vibrate into and out of the page (4) remain stationary
(4) remain stationary
Jan. 2004
+1
15 cm
Application - Noise Cancelling Headphones
(Right Click, Save As, Open)
- Paul Hewitt
(Jason P. - 2005)
(R. Meija - 2005)
(Jason P. - 2005)
|
||||||||
Task
NYSSLS Reading Passage · Waves
Sound Waves & Active Noise Cancellation
Open Reading Passage → Regents Practice Version →Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. A 3 cm pulse and a 5 cm pulse, both upright, meet in a spring. What is the amplitude when they completely overlap?
2. A +4 cm pulse meets an identical −4 cm pulse (on the opposite side). At the moment they completely overlap, the medium at that point is…
3. After two pulses pass through each other, they…
4. Noise-cancelling headphones play an “anti-noise” wave. Compared with the incoming noise, it has…
5. According to the principle of superposition, when waves overlap the resultant displacement is…
Noise-Canceling Headphones
Noise-canceling headphones have a microphone that detects outside noise. A computer chip then produces a sound wave with the same frequency and amplitude but 180° out of phase with the noise, and plays it through the speakers.
Why does the listener hear much less noise?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. After the two pulses pass through each other, what happens to them?
C2. The airplane engine hum has a frequency of 120 Hz, and the speed of sound in the cabin air is 343 m/s. Substitute numerical values into a mathematical representation that can be used to determine the wavelength of the hum. Then calculate the wavelength.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C4. On a rope, an upward pulse with an amplitude of 4.0 cm and a downward pulse with an amplitude of 6.0 cm travel toward each other. At the instant the pulses completely overlap, choose the direction of the rope’s displacement at the point of overlap and determine its magnitude.
●
C5. Two speakers emit the same tone in phase. At one point, the waves arrive with a phase difference of 360°. What is heard there?
C6. Some headphones block noise only with thick foam padding (passive), while others use destructive interference (active). Identify one benefit and one drawback of the active noise-canceling design.