Waves, Electromagnetic Waves, Light, and Sound

Waves

• is a disturbance

• moves through a medium from one location to another location

• A medium is a substance or material which carries the wave.

General Wave Properties

• All waves are traveling disturbances.

• All waves transfer energy from place to place.

Parts of a wave

• Crest and Trough

-The section of the wave that rises above the undisturbed position - crest

-That section which lies below the undisturbed position - the trough

Amplitude

• position of the medium to the top of a crest or trough.

• Height of the wave

positive and negative amplitudes

Different amplitudes

Wavelength

*crest to next crest, trough to next trough,* from the start of a wave cycle to the next starting point*Wave to wave

Ex: for wave length

Types of Waves There are three types of waves:  

-Mechanical waves.

-Electromagnetic waves

-Matter waves

Mechanical waves

• require a material medium to travel (air, water, ropes).

• These waves are divided into three different types. – Transverse waves– Longitudinal waves – Surface waves

Transverse Waves

• is perpendicular to the direction of wave propagation

• Ex: light, heat, & water waves.

Longitudinal Waves

• is parallel to the direction of wave propagation

Compression and Rarefaction

Compression• Wave that has no crests or troughs• Region where the medium become crowded or

dense• Compress – close together.• Sound waves & shock waves

Rarefaction• The less dense region

Water Waves • involve a combination of both longitudinal and

transverse motions • particle indeed travels in a clockwise circle as

the wave passes.

Electromagnetic waves

• do not require a medium to travel (light, radio

Matter waves

• are produced by electrons and particles.

Pulse and traveling or periodic wave

• a single vibration is produced is a pulse.

• moving regularly up and down, is a traveling or periodic wave . 

Measuring Waves

• The number of vibrations per second is called frequency

• Speed of the wave=Frequency X Wavelength

• is measured in hertz (Hz).

The Wave Formula• Velocity = Wavelength x Frequency .

.

• V = x f

• Velocity(m/s), Wavelength (m),

Frequency (hz)

The Nature of Sound

• Sound is caused by vibrations

• Sound waves are Compression waves

• Cannot travel through a vacuum – no particles to push around– Travels faster through liquids and solids than

gases…why?– Travels faster through warmer than cooler

substances…why?

Properties of Sound

• Key Sound Terms– Frequency: How many wavelengths pass a

point each second; hertz (Hz); high frequency=high pitch; humans 20-20,000 Hz

• Pitch: How high or low a sound seems to be

– Intensity: Amount of energy that flows through a certain area in a specific amount of time

• Loudness: Human perception of intensity

• the symbol f is frequency • the symbol T is used for period,• these equations are also expressed as:

Differences in Frequencies

Wave speed

Light wave- faster than soundEx: flying ball reaches your eyes before the

sound wave created by the bat and ball Depends on the medium• Ex: sound waves travel faster in liquids than

solid• Ex: Light waves travel slower in liquids and

solids

Calculating the wave speed

• Speed = Wavelength * Frequency• Speed-v, Frequency-F

• And Wave length -

The Nature of a Sound Wave

*Sound is a mechanical wave*Sound is a Pressure Wave*results from the longitudinal motion of the particles of the medium

Compression and rarefaction

• -As the compression (high pressure) • -rarefaction (low pressure)

Sound

• Measuring intensity of Sound– Intensity is the amount of energy in the wave– Unit of intensity is the decibel (dB)– Above 120 dB cause pain and hearing loss

• Doppler effect– The change in pitch or wave frequency due to a

moving wave source– Examples– Either the source or the observer can be moving

Doppler effect

• Doppler effect can be observed for any type of wave

• Ex: water wave, sound wave, light wave, etc

• the pitch of the siren sound was high; after the car passed by, the pitch of the siren sound was low. That was the Doppler effect

eardrum into vibration motion.

Sound/Music • Noise vs. Music

– Noise—random patterns and pitches– Music—sounds deliberately used in a regular pattern

• Musical Instruments– String vibrations of strings working with a resonator

that amplifies the sound– Brass and woodwinds vibration of air in column

working with a resonator; holes and valves or changing the length of the air column

– Percussion vibration of the membrane causes air inside to vibrate

Sound

• Ultrasound– Medicine high frequency sound waves to

detect and monitor such things as pregnancy, heart disease, and cancer;

– can be used to break up kidney stones and gall stones

Radio Communication

• Radio transmission– Each station is assigned a unique frequency

(called a carrier wave)– FM (frequency modulation); AM (amplitude

modulation); higher frequencies than AM– Article page 405

Behavior of Waves• Types of Interference

– Occurs when two waves combine into one– Constructive: the wave gets bigger

because the crest and trough overlap– Destructive: the wave gets smaller

because a crest and a trough overlaps

Properties of Sound

Intensity:Is the amount of energy that flows through a certain area in a specific amount of time.High intensity carries high energy

Loudness:Is the human perception of the intensity.The intensity of the sound increases, the loudness of the sound you hear increases.

Ultrasonic wave

• Humans can’t hear sound frequencies above 20,000 Hz, called ultrasonic waves.

• Used in medical diagnosis and treatment.

Infrasonic waves

• Is also called subsonic wave

• Have frequencies below 20 Hz

• Too low to hear

• May feel them as a rumble inside your body

• Resonance:

• is the ability of the medium to vibrate by absorbing energy at its own natural frequency.

• Resonance helps amplify the sound created in many musical instrument

• Music:

• Is made of sounds that are deliberately used in a regular pattern.

• Musical instruments contain strings , membranes or columns of air- something that vibrates at its natural frequency to create a pitch.

• Natural frequency depends on the string’s thickness and length and how tightly it is stretched