Waves Sound & Light

Sound Sound travels in waves (“sound waves”) Sound waves are mechanical waves Mechanical waves are waves that require a medium to travel through (cannot occur in a vaccuum) So if you suck all the air out of a room, and ring a bell… you won’t hear a sound!

Sound Sound waves are also longitudinal (compression) waves. They are caused by vibrations of particles- or the moving back and forth of an object.

Sound Amplitude: the maximum distance of a wave from rest position Recall that the larger the amplitude of a wave, the more energy that wave has… In sound waves, amplitude can make a sound have a higher or lower volume. Pitch: how high or low a sound seems Frequency: the number of wave cycles per unit of time (measured in Hertz)

Sound One more way sounds differ? QUALITY! Pleasant sounds have regular wave patterns. Noise has irregular wave patterns that may not repeat.

How do we hear? Sound waves cause your eardrums to pound, and these vibrations are sent to the inner ear. Small hairs inside your ear move back and forth with the vibrations of sound in the air. The brain perceives these vibrations as sound.

Range of Hearing Sound intensities are measured in units called decibels. The threshold of hearing begins at 0 dB and extends to the threshold of pain at 130 dB. Listening to sound at 90 dB for an extended period of time can cause hearing damage.

Decibel Sound Scale Decibels Sound 180 Rocket launching pad 140 Jet plane Gunshot blast 120 Automobile horn 130 Pain threshold Discomfort 90 Subway 80 Noisy Restaurant 75 Busy traffic 66 Normal conversation 50 Average home 30 Soft whisper Source: Lee, K.J., Essential Otolaryngology, 8th edition, New York: McGraw-Hill, 2003.

The Doppler Effect Why does the siren of an ambulance sound different as it approaches you, and as it passes you? This is because of the Doppler Effect. As the distance between the source of the sound and receiver increases, sound waves stretch out. The sound becomes lower the further away the receiver is.

Light Light also travels in waves. These waves are called electromagnetic waves. Electromagnetic waves are a combination of magnetic and electrical field waves Electromagnetic waves can travel through a vacuum (empty space).

Light Electromagnetic waves are transverse waves.

Light Electromagnetic waves have properties of both particles and waves. This is why they have such unique properties. For example, Polarization

Why is it better to wear polarized sunglasses? Ultraviolet radiation is harmful to your eyes, and can cause damage with too much exposure.

Light The speed of light has been measured! It is: 3.00 x 108 m/s

The Electromagnetic Spectrum Although all light travels at the same speed, different wavelengths and frequencies are possible. All of these waves together make up the electromagnetic spectrum. The spectrum ranges from radio waves to gamma rays.

The Electromagnetic Spectrum Note that visible light is only a very small part of the spectrum!

Radio Waves Wavelengths of radio waves range from 1000 kilometers to 1 millimeter. Therefore, radio waves have the lowest frequencies. AM (amplitude-modulated) radio has longer wavelengths than FM (frequency-modulated) radio. TV waves are all over the radio wave range.

Microwaves These waves have wavelengths that range from centimeters to feet. Microwave ovens and cell phones use microwaves to function.

Infrared Waves Infrared wavelengths range from about 400 nanometers to 1 mm. We use infrared waves to in heat sensors and heat vision goggles, to see where heat is concentrated.

Visible Light Visible light wavelengths range from 700 (red) to 400 nm (violet). These are the colors we see. ROYGBIV

Ultraviolet Light UV light has wavelengths from about 400 nm to 1 nm. UV light is used in black lights, which can be used to kill bacteria. UV light from the sun helps our skin to produce vitamin D. However too much UV light causes sunburns and can lead to cancer.

X-Rays X-Rays have wavelengths between about 3 and 0.03 nm. They are used to look at pictures of our bones and teeth (these are more dense than skin, and absorb x-rays better). Lots of things in space emit X-rays.

Gamma Rays Gamma ray wavelengths get no larger than 0.03 nm. These rays are found in space. They are not commonly used because they are so energetic, they’re difficult to work with.