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 sound Ex: 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