Wave Behaviors: Reflection, Interference, and Resonance
Wave Behaviors, Part 1
Learning Goal 8.2: Describe various wave behaviors and give examples in the context of light or sound.
Why Waves?
Why do we model certain things (sound, light) as a wave? What makes a wave a wave?
Waves exhibit certain behaviors that are distinct from the behavior of objects:
- Reflection
- Interference
- Doppler effect
- Refraction
- Diffraction
Reflection
Reflection: when a wave bounces back at a boundary
Refer back to part 1 of the investigation. How does a wave reflect differently at a fixed (closed) end vs. at a loose (open) end? Do waves bounce off each other, or do they pass through each other?
- Wave reflects from a fixed end: Pulse inverts as it reflects.
- Wave reflects from a free end: Pulse reflects without inverting.
Interference
Interference: when multiple waves pass through the same space simultaneously
Two Types of Interference
Constructive interference:
when two waves add together to a greater amplitude
Destructive interference:
when two waves subtract or cancel out
Standing Waves
Standing waves: waves that seem to oscillate in place; they form when waves with the right wavelength reflect and interfere within a closed medium
Nodes and Antinodes
- Nodes: locations of destructive interference where particles don’t move at all
- Antinodes: locations of constructive interference where the wave has its maximum amplitude
Diagram: A N A N A N A N
Resonance
Natural frequency: the frequency at which an object will naturally oscillate when disturbed
Resonance: a condition that occurs when the frequency of an applied force matches an object’s natural frequency, causing constructive interference and an increased amplitude of vibration
Check Your Understanding
Auditoriums sometimes have dead spots where an audience member cannot hear the performers. Which wave behavior best explains this phenomenon?
b. interference (specifically destructive interference)
Additional Links
- Physics of Tuning
- Light as Electromagnetic Wave