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: Ripples on the surface of a pond

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