13.1 : wave basics / wave properties · waves phases wave phases • a waves phase is the position...

13.1 : Wave Basics / Wave Properties

•  Waves •  Mechanical Waves •  Amplitude •  Frequency / Period •  Wavelength •  Wave Phases •  Wave Speed

Medium A medium is the material, which a wave travels through (Solid, liquid, or a gas). Examples: o  The medium of a water wave is the water o  The medium of a sound wave is the air o  The medium of a wave on a string is the string

Waves

Pulse A single disturbance in a medium What is a wave? •  A wave is a vibration or disturbance that propagates

though a medium or space.

•  A series of pulses

•  A waves “job” is to carry energy from one point to another.

•  All waves transfer energy but not mass.

Waves

2 Types of Waves: Mechanical A mechanical wave is created when a source of energy causes a vibration to travel though a medium. Example: Sound Waves Electromagnetic Waves that do not need a medium (matter) to transfer energy Example: Light Waves (Section #14)

Waves

•  Uses matter (medium) to transfer energy. •  The energy is transferred from particle to particle as they

collide

Mechanical Waves

There are 2 types of Mechanical Waves: Transverse Waves •  Medium vibrates perpendicular (90º) to the direction the

energy travels

Mechanical Waves

Transverse Waves Examples:

1.  Shaking the end of a rope up and down 2.  Shaking one end of the blanket up and down 3.  Wave in the ball park

Transverse Waves

Transverse Waves Properties Crest The highest point of the wave above the rest position. (The top of the “hill”) Trough The lowest point of the wave below the rest position. (The “valley” of the wave)

Transverse Waves

Longitudinal Waves A wave in which the medium vibrates parallel to the direction the energy travels. (sound)

Longitudinal Waves

Longitudinal Wave Properties Compression An area where the particles in a medium are spaced close together. Rarefaction An area where the particles in a medium are spread out.

Longitudinal Waves

Longitudinal Waves Properties

Longitudinal Waves

Longitudinal Waves Examples:

1.  Waves produced by earthquakes 2.  Sound Waves 3.  Ultrasound

Longitudinal Waves

Longitudinal Waves

Transverse and Longitudinal Waves

Amplitude The maximum distance (m) from the rest position of a wave to the top of a crest or the bottom of a trough.

Wave Characteristics

Amplitude The greater the amplitude of a wave then the more energy it is carrying

Wave Characteristics

Frequency Number of wavelengths to pass by a given point in 1 second Symbol: f Units: Hz

Wave Characteristics

f = #of _waves#of _seconds

Which one of these waves has a higher frequency?

Wave Characteristics

Period The time required for one complete wave to pass a certain point. Symbol: T Units: seconds

Wave Characteristics

T = #of _seconds#of _waves

Period and Frequency Relationship

T = 1f f = 1

T

Wave Characteristics

Example #1 10 complete waves pass in 5 seconds

a.  What is the frequency of the wave? b.   What is the period of the wave?

f = 2 Hz T = 0.5 seconds

Wave Characteristics

Wavelength Length of one complete wave.

o  1 complete wave ~ 1 whole crest AND 1 whole trough Symbol: λ (lambda) Units: m

Wave Characteristics

Wavelength

Wave Characteristics

Wavelength

Wave Characteristics

Note: When frequency increases, wavelength decreases.

Wave Characteristics

Which one of these waves has a larger wavelength (λ)?

Wave Characteristics

Exercise Draw two waves that have the same amplitude but different wavelengths.

Wave Characteristics

Exercise Draw two waves that have the same wavelength but different amplitudes.

Wave Characteristics

Waves Phases

Waves Phases

Wave Phases •  A waves phase is the position of a point in time (an instant) on

a waveform cycle.

•  A complete cycle is defined as the interval required for the waveform to return to its “initial position”.

•  The graph below shows how one cycle constitutes 360º of phase.

Waves Phases

Phase difference

Here the phase difference is ½ a wavelength which is 180º

Phase difference between waves •  Waves of same amplitude, wavelength, frequency, can still be

“different”. •  There can be phase differences between waves

Waves Phases

Waves Phase

Which points are in phase with point “A”? “E” and “I” Which Points are in phase with point “C”? “G”

Waves Phase

Which Points are 180º out of phase with “A”? “C” and “G” Which Points are 90º out of phase with “B” and “F”? “A”, “C”, “E”, and “G”

Waves Phase

A

B

C

D

E

F

G

H

I

Exercise Label the points on the waveform next to the degree they represent in the circle

Formula V = f x λ Speed: m/s Frequency: Hertz (Hz) Wavelength: meters (m)

Wave Speed The speed of a wave is how fast the wave is traveling

Wave Speed

Wave Speed Problems

Example #1 A sound wave in a steel rail has a frequency of 620 Hz and a wavelength of 10.5 m. What is the speed of sound in steel?

V = f x λ V = 620 hz x 10.5 m 6,510 m/s

Wave Speed Problems

Example #2 What is the speed of a wave with a frequency of 760 Hz and a wavelength of 0.45 m

V = f x λ V = 760 hz x 0.45 m 342 m/s

Wave Speed Problems

Example #3 A wave has a period of 0.25 seconds and a wavelength of 3 meters. What is the speed of the wave?

V = f x λ V = 4 hz x 3 m 12 m/s

Wave Speed Problems

Example #4 The wave below has a period of 0.05 seconds. What is the speed of the wave?

V = f x λ V = 20 hz x 4 m 80 m/s