20.3 Wave Interference and Energy
Date, Section, Pages, etc.
Mr. Richter
Agenda
 Warm Up
 Collect Labs
 Review HW
 Introduction to Interference
 Notes:
 The Superposition Principle
 Waves and Energy
Objectives: We Will Be Able To…
 Describe the superposition principle with constructive and
destructive interference.
 Explain which properties affect wave energy and why.
Warm-Up:
 Can two waves be in the same place at the same time?
 If yes, what do you think happens there?
 If not, why not?
The Superposition Principle
The Superposition Principle
 Waves are not physical things.
They are energy.
 This means the more than one
wave can exist in the same
place at the same time.
 Think about sound: can you
hear more than one thing at
once?
 Of course!
The Superposition Principle
 When waves collide, their vibrations combine.
 The superposition principle states that the total vibration at
any point is the sum of the vibrations of each individual
wave.
The Superposition Principle:
Constructive Interference
 Constructive interference
occurs when two wave pulses
combine to make a larger
amplitude.
 Example: if the number of
guitars playing the same note is
doubled, the amplitude is
increased (it gets louder!)
The Superposition Principle:
Destructive Interference
 Destructive interference
occurs when two wave pulses
combine to make a smaller
amplitude.
 Example: noise-cancelling head
phones.
Waves and Energy
Waves and Energy
 Reminder: the main idea about waves –
 Waves transfer energy from place to place without
transferring matter.
 There are two factors that affect the energy of a wave:
 frequency – how often the energy arrives
 amplitude – how much energy arrives each time
Waves and Energy: Frequency
 The greater the frequency
of a wave, the more energy
it carries.
 Wave energy is
proportional to frequency.
 Example: trying to whip a
rope more often.
Waves and Energy: Amplitude
 The greater the amplitude
of a wave, the more energy
it carries.
 Wave energy is
proportional to amplitude.
 Example: turning up the
volume.
Wrap-Up: Did we meet our objectives?
 Describe the superposition principle with constructive and
destructive interference.
 Explain which properties affect wave energy and why.
Homework
 p. 447 #1, 2, 4, 5