17.5 Behavior of Waves

17.5 Assessment Quiz

Take a minute to look through your notes. Ø  There are 15 questions Ø  All answers Multiple Choice Ø  You do NOT need a calculator or formula sheet Ø  Notes CAN NOT be used on the assessment

Reflection

Reflection   §  Reflection occurs when a wave bounces off a surface that it

cannot pass though

§  Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down. 

Reflection

Reflection Examples:  

1.  Ball thrown against a wall 2.  Mirror 3.  Reflection in a pool of water

 

Refraction

Refraction §  The bending of a wave as it enters a new medium at an

angle

§  Refraction occurs because one side of the waves moves more slowly than the other side

Refraction

Refraction Examples:

1.  Fish in the water 2.  Straw in a glass of water 3.  Light passing thru a prism

Refraction

Refraction

Swimming pool example

Diffraction

Diffraction §  The bending of a wave as it moves around an obstacle or

thru a narrow opening.

§  A wave diffracts more if its wavelength is large compared to the size of the opening or obstacle

 

Diffraction

Diffraction

Diffraction

Interference

§  Occurs when two or more waves overlap and combine together.

§  2 types of interference are constructive interference and destructive interference.

Constructive Interference

Two or more waves combine to produce a wave with a larger displacement.

Constructive Interference

Destructive Interference

Two or more waves combine to produce a wave with a smaller displacement.

Destructive Interference

•  the result of two or more sound •  waves overlapping

Interference

Standing Waves

A wave that appears to stay in one place – it does not seem to move through the medium     Example Two people shaking either end of a jump rope. If they shake in sync the rope can form a regular pattern of waves oscillating up and down.

Standing Waves

Sound waves are longitudinal waves. Behaviors of sound can be explained with a few properties:

§  Speed §  Intensity §  Loudness §  Frequency §  Pitch

Sound and Hearing

In dry air at 20ºC, the speed of sound is 340 m/s. (660 mph) Sounds waves travel:

§  faster in solids §  slower in liquids §  slowest in gases

  This is due to the particles in a solid are close together and the speed of sound depends directly on the density of the medium.

Sound - Speed

Sound - Speed

Sound – Intensity and Loudness

Sound intensity depends of the waves amplitude and distance from the sound source. Example: When someone whispers in your ear, the sound intensity may be greater than when someone shouts at you from the other end of a field.

Sound – Intensity and Loudness

Sounds Intensity is measured in decibel (dB)   Normal room conversation is: 40-50 dB   Pain will occur at: 120 dB    Loudness is a physical response to the intensity of sound.   •  As intensity increases, loudness increases •  Varies per person’s health of ears and how your brain

interprets information.

Sound – Frequency and Pitch

The frequency of a sound wave depends on the how fast the source of the sound is vibrating.   Musical instruments are examples of objects producing different frequencies   •  The trumpet can produce higher frequency by changing

the length of the tubing which air moves •  The air forms a standing wave •  The longer the tube, the longer the wave length and the

standing wave, the lower the frequency of the note produced

Sound – Frequency and Pitch

The pitch is frequency of sounds as you perceive it.   High frequency sounds have a high pitch   Low frequency sounds have a low pitch   •  Pitch depends on other factors such as age and the

health of your ears  

Sound – Frequency and Pitch

Which tube has the highest pitch sound? •  The shortest tube

Which tube has the lowest pitch sound? •  The longest tube

UltraSound

Most people can hear between 20 hertz and 20,000 hertz   Infrasound (0-20 Hz) is sound at frequencies lower than most people can hear   Ultrasound (20,000 Hz and above) is sound at frequencies higher than most people can hear

A change in sound frequency caused by motion of the sound source, motion of the listener, or both. •  As a source of sound approaches, an observer hears a

higher frequency

•  When the sound source moves away, the observer hears a lower frequency

Doppler Effect

Doppler Effect

Doppler Effect – Single Person

Doppler Effect Doppler Effect – Two People

Doppler Effect

Doppler Effect

Doppler Effect

Doppler Effect

Car Horn: https://www.youtube.com/watch?v=a3RfULw7aAY

Big Bang Theory https://www.youtube.com/watch?v=z0EaoilzgGE

17.5 Assessment

Question #1 How is a wave changed by reflection? Does not change speed or frequency, but can be flipped upside down   Question #2 What caused refraction when a wave enters a new medium? One side of the wave is moving slower

17.5 Assessment

Question #3 What determines how much a wave diffracts when it encounters an opening or obstacle? If its wavelength is large compared to the size of an opening   Question #4 List the types of interference •  Constructive •  Destructive

17.5 Assessment

Question #5 What is the speed of sound in dry air? 340 m/s   Question #6 What state of matter does sound move the fastest and slowest? •  Fastest – Solids •  Slowest - Gases

17.5 Assessment

Question #7 What two properties does sound intensity depend on?   •  Waves amplitude •  Distance from the source    Question #8 What are the units for sound intensity? Decibels (dB)

17.5 Assessment

Question #9 What is the normal sound intensity range? 40-50 dB    Question #10 What is the normal range (in hertz) that people can hear? 20 - 20,000 Hz

17.5 Assessment

Question #11 How does a musical instrument produce notes at different pitches? Length of the tube

Question #12 What is the Doppler Effect? A change in sound frequency caused by motion of the sound source, motion of the listener, or both.

17.5 Assessment

Question #13 What is type of wave is a sound wave? Longitudinal