Waves 9 1 The Nature of Waves Waves

Waves

9 -1 – The Nature of Waves • Waves Defined • Wave – • Ex: • Waves and Energy • Waves transfer energy, not matter

9 -1 – The Nature of Waves • A medium is a substance or material which carries the wave. • Electromagnetic Waves are the exception, they do not need a medium to travel.

9 -1 – The Nature of Waves • Mechanical Waves • Transverse Waves • Ex: • Longitudinal Waves • Ex:

9 -2 – Wave Properties • • Parts of a Wave

9 -2 – Wave Properties • Wavelength –

9 -2 – Wave Properties • Wavelength and Frequency • Inverse relationship

9 -2 – Wave Properties • Calculating Frequency • Frequency (Hz) = # of waves time (s) • Calculating Wavelength • Wavelength= 1/ frequency

9 -2 – Wave Properties • Calculating Frequency Calculate the frequency of this wave if it occurs over 2. 5 seconds.

9 -2 – Wave Properties • Calculating Frequency • A ruby-throated hummingbird beats its wings at a rate of about 70 wing beats per second. What is the frequency in Hertz of the sound wave?

9 -2 – Wave Properties • Calculating Frequency • Joe counts waves as they pass a lighthouse. If he counts 15 waves occurring over 4. 1 seconds, what is the frequency of the waves?

9 -2 – Wave Properties • Calculating Frequency • A buoy bobs up and down in the ocean. The waves have a wavelength of 2. 5 m, and they pass the buoy at a speed of 4. 0 m/s. What is the frequency of the waves?

9 -2 – Wave Properties • Calculating Speed • V = f • Velocity (m/s) = frequency (Hz) x wavelength (m)

9 -2 – Wave Properties • • • Calculating Speed A wave traveling in the water has a frequency of 250 Hz and a wavelength of 6. 0 m. What is the speed of the wave?

9 -2 – Wave Properties • Calculating Speed • The lowest pitch that the average human can hear has a frequency of • 20. 0 Hz. If sound with this frequency travels through air with a speed • of 331 m/s, what is its wavelength?

9 -2 – Wave Properties • Calculating Speed • A ship anchored at sea is rocked by waves that have crests 14 m apart. • The waves travel at 7. 0 m/s. How often do the wave crests reach the • ship?

9 -2 – Wave Properties • Ocean Waves are a transverse and longitudinal wave in one • Acts as both:

9 -2 – Wave Properties • Amplitude – • Tells about the energy of a wave

Ch 10 - Sound • What causes sound? • Vibrations, Create longitudinal waves • Energy from wave transferred to your eardrum • Your brain interprets this as sound

Ch 10 - Sound • Frequency of sound wave determines pitch (high, low)

Ch 10 - Sound • Instruments create different pitches in different ways • Change length of instrument’s tube by opening holes (wind instruments) • Change length of vibrating string (guitar, violin)

Ch 10 - Sound • Speakers turn electrical energy into sound waves • Vibrating cone inside speaker produce sound waves

Ch 10 - Sound • Radio waves are used in radios. • AM radio waves are measured in kilohertz (k. Hz) • FM radio waves are measured in megahertz (MHz) • Cell phones operate in gigahertz (GHz)

Ch 10 - Sound • We cannot hear sound in outer space. • Sound waves need particles in a solid, liquid, or gas to vibrate • No air in outer space for sound waves to vibrate.

Ch 10 - Sound • Speed of Sound depends on • Wind conditions • Temperature • Humidity • How fast does sound travel? • 330 meters per second (dry air, 00 C) • Faster in liquids (4 x faster) • Even faster in solids (15 x faster)

Ch 10 - Sound • Frequency and pitch have a direct relationship • Amplitude and loudness have a direct relationship

Ch 10 - Sound • The Doppler Effect • Perceived change in wavelength, frequency, and pitch due to a moving object • No actual change in sound, just perceived change due to the object moving toward you, then away from you.

Ch 10 - Sound • Refraction of Sound • Bending of wave due to speeding up or slowing down • Change in Medium

Ch 10 - Sound • Reflection of Sound Waves(Sound waves bouncing) • Waves reflect at the same angle that the wave hits (law of reflection) • Echoes work on this principle. • Theaters and concert halls are designed to reduce echoes.

Ch 10 - Sound • Applications of Reflected Waves • Sonar “sound navigation ranging” • Sonography • Ultrasound • Echolocation

Ch 10 - Sound Waves Electromagnetic Waves Cannot travel in a vacuum Particles compress and relax as the wave travels through Are longitudinal waves that transmit energy Produce vibrations which can be sensed and some heard Have crests, troughs, and a resting equillibrium Reflect, refract, and are absorbed Can travel in a vacuum Have a dual quality (particles and energy) Are transverse waves that transmit energy Only portion of electromagnetic waves are visible

Electromagnetic Spectrum- Visible • Electromagnetic Waves • Are part magnetic field and part electric field • Have properties of both waves and particles • Can travel without a medium • All travel at the same speed (speed of light)

Electromagnetic Spectrum- Visible • Electromagnetic Spectrum • Organizes electromagnetic waves according to frequency • Also shows the wavelength of various waves • Remember relationship between frequency and wavelength • We can only see one small portion of the EM spectrum

Electromagnetic Spectrum- Visible

Electromagnetic Spectrum- Visible • Visible Spectrum • Filters allow certain colors to pass, block others

Electromagnetic Spectrum- Visible • Visible Spectrum • We see colors based on those absorbed and those reflected • Red car = Red light reflected • White car = all colors reflected • Black car = all colors absorbed

Electromagnetic Spectrum- Visible • Visible Spectrum • Opaque objects • Reflect the light • Cannot see through opaque items

Electromagnetic Spectrum- Visible • Visible Spectrum • Translucent objects • Reflect some light, transmits some light • Can somewhat see through translucent items

Electromagnetic Spectrum- Visible • Visible Spectrum • Transparent objects • Transmits light • Can see through transparent items

Electromagnetic Spectrum- Non. Visible • Rest of the Electromagnetic Spectrum (excluding visible light)

Electromagnetic Spectrum- Non. Visible • Radio Waves • Lowest-energy, lowest frequency, largest wavelength • Transmit radio, tv, and cellular signals • Sources: electric circuits

Electromagnetic Spectrum- Non. Visible • Microwave Waves • Lower-energy, lower frequency, larger wavelength • Used to heat food, used in radar guns • Sources: special vacuum tubes, like those in microwave ovens

Electromagnetic Spectrum- Non-Visible • Infrared Waves • Low-energy, low frequency, large wavelength • Heat emitted from warm objects, used in special cameras • Sources: anything that gives off heat

Electromagnetic Spectrum- Non-Visible • Ultraviolet (UV) Waves • high-energy, high frequency, small wavelength • Emitted from the sun, very hot objects, like sun lamps • Sources: special vacuum tubes, like those in microwave ovens

Electromagnetic Spectrum- Non-Visible • X-ray Waves • higher-energy, higher frequency, smaller wavelength • Emitted from x-ray machines, used to image people’s bones • Detected through high speed collisions between electrons

Electromagnetic Spectrum- Non-Visible • Gamma Ray Waves • highest-energy, highest frequency, smallest wavelength • Emitted from nuclear reactions • Sources: radioactive substances • Can be detected with a Geiger counter.