Unit 10 “Waves and Wave Properties” Test Review

A wave is … …a motion of disturbance Waves “propagate in 3-dimensions”.

General Wave Form crest trough

Label the following examples as transverse or longitudinal waves.

There are 2 Categories of Waves Mechanical Waves Electromagnetic Waves Need a medium to travel through. Can travel without a medium For example, through gas, liquid or solids For example, through a vacuum

Velocity = frequency x wavelength Wave Speed Equation V=fλ Velocity = frequency x wavelength

Frequency, Wavelength & Speed

Which wave has the higher frequency? Which wave has the higher speed? Same Speed!

Which wave has the higher wavelength? Which wave has the higher speed? Same speed! higher wavelength

Sound and Light Waves Sound travels at approximately 340m/s in air. Light travels at 300,000,000m/s (3x108m/s) in a vacuum. Because light travels faster than sound, you can SEE distant explosions before you can hear them. (Light a bomb blast, or thunder/lightening) Light can travel in a vacuum --- sound cannot travel in a vacuum. So in outer space you can SEE things – but you can’t hear them! A distant explosion you would see – but you couldn’t hear the blast.

Find the Speed of Sound for the sound wave each tuning fork creates. Frequency (f) Hz Wavelength (λ) m Velocity (V) m/s 600 0.600   300 1.20 360 360 Does the frequency change the speed of sound? (Use data to support) What does change when the frequency changes? (Use data to support) The speed of sound in 25oC air is 346m/s. According to your answer for the speed of sound above, do you think this room the lab was completed in was hotter or colder than 25oC? No, a change in frequency does not change the speed of sound. The only way to change the speed of sound is the change the medium. For both frequencies of 600Hz and 300Hz the speed of sound remained constant, 360m/s. A change in frequency changes the wavelength. An increase of frequency means a decrease in wavelength, they are inversely proportional. For example, a frequency of 600Hz has a small wavelength of 0.600m. But if the frequency decreases to 300Hz, the wavelength increases to 1.20m! Hotter, because the speed is faster than 346m/s

Choose which of the following factors change when a sound’s “loudness” changes and which changes when the “pitch” changes. ¤ Intensity ¤Speed of the sound wave ¤ Frequency ¤ Decibel level ¤ Wavelength ¤ Amplitude Intensity Frequency Decibel Level Wavelength Amplitude Loudness Pitch Intensity Frequency Decibel Level Wavelength Amplitude Speed of the Sound Wave: Doesn’t change when the sound gets louder or the pitch changes. Speed only changes if the medium changes!

Interference “The Superposition Principal” Constructive Interference Bigger Wave Amplitude Destructive Interference Smaller Wave Amplitude

Standing Waves: a wave reflects off a boundary and interferes constructively. Antinode: A point in a standing wave which has the maximum amplitude. Node: A point in a standing wave which has no amplitude.

The Doppler Effect An apparent change in frequency due to relative motion. Examples: Car music/horn as it drives by Police sirens Sonic Boom! (Breaking the sound barrier) Red shift and blue shift with light waves High frequency (moving towards) Low frequency (moving away)

High frequency means high pitch! Low frequency means low pitch! Doppler Effect – Sound Waves The Doppler effect makes sources of sound appear to be higher and lower pitch based on their relative motion. Moving towards– higher frequency Moving away from – lower frequency High frequency means high pitch! Low frequency means low pitch!

The frequency changes due to relative motion – this results in seeing… Doppler Effect – Light Waves The frequency changes due to relative motion – this results in seeing… higher frequency waves (bluer waves) (moving towards) lower frequency (redder waves) (moving away)

This is what the line spectra for red or blue shift would look like. Doppler Effect – Light Waves This is what the line spectra for red or blue shift would look like.

Electromagnetic Spectrum “Light Waves” Light waves can travel through a vacuum Speed of Light in a vacuum: 300,000,000m/s If the light moves through a medium, when the medium changes, the speed of light changes. Different types of Electromagnetic Waves have different properties. These properties are based on their frequency and wavelength. f λ f λ High Energy Waves Low Energy Waves

f λ f λ Low Energy Waves High Energy Waves

Properties of EM Waves Radio Waves Microwaves Infrared Rays Communication (Radio, telephones, television) GPS (Global Positioning System) Microwaves GPS Radar Microwave Ovens Infrared Rays Heat produces infrared light Night Vision (sees “heat”)

Properties of EM Waves Visible Light Red, Orange, Yellow, Green, Blue, Indigo, Violet ROY G BIV Seeing, cameras, telescopes, colors. White light is a mix of ALL colors. Black is the absence of light (no light!)

Properties of EM Waves Ultraviolet Rays (UV) X-Rays Gamma Rays High Energy, penetrate your skin. Sunburn, skin cancer Used to disinfect medical equipment X-Rays Higher Energy, penetrate your skin, your muscles and tissues. Can reflect off bones so you can see inside your body! Gamma Rays Highest Energy, penetrates through your body. From nuclear reactions, very dangerous, can kill, cause cancer. Also used to treat cancer!

What is the minimum frequency of sound waves required for the bat to detect an insect that would reflect a wavelength of 0.0057m? (Assume the speed of sound is 340m/s). The red light emitted by a He-Ne laser has a wavelength of 633 nm in air and travels at 3.00x108m/s. Find the frequency of the laser light. What is the frequency of a sound wave produced by a flute playing C-note if the wavelength is 21m? What is the wavelength of a radar signal that has a frequency of 33 GHz? The answer should be f = 59649 Hz The answer should be f = 4.74x1019 Hz The answer should be f = 16.2 Hz The answer should be λ= 0.00909m