waves and wave characteristics. what is a wave? a wave is a disturbance or vibration that carries...
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Waves and
Wave Characteristics
What is a wave?
• A wave is a disturbance or vibration that carries energy without carrying matter.
• Examples:– Ripples on the surface of a pond– sound in air– visible light– Seismic Waves (Shock Waves)– X rays – Radio Waves– infrared rays
Example: sound in air
Example: visible light
Example: Seismic Waves (Shock Waves)
Example: X-Rays
Example: Radio Waves
What is a wave?
• In physics, a wave is a traveling disturbance that travels through space or matter bringing energy from one place to another.
• It is important to remember that waves transfer energy, not matter
What is a wave?
• Traveling disturbance in water molecules
What is a wave?
• The energy (disturbance) travels, not the water
What is a wave?
• Have you ever "done the wave" as part of a large crowd at a football or baseball game?
• A group of people jumps up and sits back down, some nearby people see them and they jump up, some people further away follow suit and pretty soon you have a wave travelling around the stadium.
• The wave is the disturbance (people jumping up and sitting back down), and it travels around the stadium.
• However, none of the individual people the stadium are carried around with the wave as it travels - they all remain at their seats.
What is a wave?
• The energy (disturbance) travels, not the people:
What is a wave?
• Sound waves in air behave in much the same way.
• As the wave passes through, the particles of the air move back and forth but it is the disturbance which travels, not the individual air molecules.
What is a wave?
• Transverse waves on a string are another example.
• The string is displaced up and down as the wave travels from left to right, but the string itself does not experience any net motion
Mechanical Waves:
• Mechanical waves are waves that need a substance (medium) to travel through
• Examples:– Sound traveling through air or water– Seismic waves traveling through the Earth– Vibrations traveling through the table top
Electromagnetic Waves:
• Electromagnetic waves are waves that do not need a substance (medium) to travel through
• Examples:– Light traveling through space– Radio waves communicating with a space station– X rays
Transverse Waves:
• A wave that vibrates at a 90° angle to the direction of the wave.
Transverse Waves:
• A wave that vibrates at a 90° angle to the direction of the wave.
Transverse Waves:
• The center line of a transverse wave represents the position of the medium when it is undisturbed.
Parts of a wave: Crests and Troughs
• Crest – the part of a wave above the centerline• Trough – the part of a wave below the centerline
Trough Trough
CrestCrest
Wave Characteristics: Wavelength
• Wavelength is the distance of one complete wave
• It is usually measured meters
Wave Characteristics: Wavelength
• Wavelength is the distance of one complete wave• It can be measured crest to crest or trough to
trough
Wave Characteristics: Amplitude
• Amplitude is how tall a crest is from the center line (or how deep it is from the centerline)
Wave Characteristics: Amplitude
• The higher the Amplitude of a wave, the more energy the wave has
High Amplitude = High Energy
Low Amplitude = Low Energy
Wave Characteristics: Frequency
• Frequency – the number of waves that go by in one second
• Frequency is measured in Hertz (Hz)
Wave Characteristics: Frequency
Animations:
• http://www.stmary.ws/HighSchool/Physics/home/animations3/waves/Wave_Characteristics.html
Wave Characteristics: Period
• Period: time for an entire wave cycle to pass a given point • the amount of time it takes for one wave to pass by• Period is measured in seconds (s)
Wave Characteristics: Period
Wave Characteristics: Period
• http://www.stmary.ws/HighSchool/Physics/home/notes/waves/PeriodAmplitude.htm
Wave Characteristics:
f = frequency units: Hz (Hertz)
λ = wavelength units: m (meters)
v = speed units: m/s
v = f ∙ λ f = v ÷ λλ = v ÷ f
A wave has a frequency of 88Hz and a wavelength of 4 meters. What is its speed in m/s?
Given Unknown Equation Solution
f = 88 Hzλ = 4 m v = ? v = f ● λ
v = f ● λ v = 88 ● 4
v = 352 m/s
Scientific Units
A wave has a speed of 450 m/s and a wavelength of 0.2 meters. What is its frequency in Hz?
Given Unknown Equation Solution
v = 450 m/sλ = 0.2 m f = ? f = v ÷ λ
f = v ÷ λ f = 450 ÷ 0.2
f = 2250 Hz
Scientific Units
A wave has a speed of 120 m/s and a frequency of 600 Hz. What is its wavelength in meters?
Given Unknown Equation Solution
v = 120 m/sf = 600 Hz λ = ? λ = v ÷ f
λ = v ÷ f λ = 120 ÷ 600
λ = 0.2 m
Scientific Units
Wave Characteristics:
f = frequency units: Hz (Hertz)
T = period units: s (seconds)
T = # of Waves T = 1 ÷ f time
5 ocean waves pass by a boat in 25 seconds. What is the period of the waves?
Given Unknown Equation Solution
# = 5t = 25 s T = ? T = # waves
time
T = # ÷ t T = 5 ÷ 25
T = 0.2 s
Scientific Units
The frequency of a sound wave is 20 Hz. What is the period of the waves?
Given Unknown Equation Solution
f = 20 HzT = ? T = 1/f
T = 1 ÷ f T = 1 ÷ 20
T = 0.05 s
Scientific Units