Sound, Light, Electromagnetic Spectrum and Mirrors

Sound Sound waves are compressional waves. Two regions: compressions and rarefactions Sound travels faster in liquids and solids than in gases. Why? The molecules in liquids and solids are closer together.

Sound Humans hear sound waves in a limited frequency range. 20 Hz-20,000 Hz Other ranges: dolphins 70 Hz-150,000Hz Dogs 40 Hz-46,000 Hz Infrasound-any sound lower than 20 Hz Ultrasound- any sound higher than 20,000Hz Ultrasound imaging is used in medicine Sonar- is a system that uses reflected sound waves to determine distances & location of objects Bats use sonar to navigate in flight & locate food

Ultrasound imaging used in medicine-echoes of very high frequency ultrasound waves between 1million-15 million Hz are used to produce computerized images called sonograms. Bats use sonar to navigate in flight & locate food

Loudness is determined by… the amount of energy in the wave As the energy ↑, the amplitude of the wave will ↑ Your distance from the source the sound waves Intensity of a sound describes its loudness Intensity is measured in decibels(dB)

The Doppler Effect The observed change pitch or wave frequency due to a moving wave source. You hear the high pitch of the siren of the approaching ambulance, and notice that its pitch drops suddenly as the ambulance passes you. That is called the Doppler effect. Pg 331 Figure 9

Doppler Effect The sound is louder due to wave compressions The sound is lower due to wave rarefactions.

Electromagnetic Waves Electromagnetic waves are made by vibrating electric charges and can travel through space where matter is not present. Electromagnetic waves do not require a medium.

The Electromagnetic Spectrum Gamma rays –short wavelengths and high frequency- very powerful and dangerous Radio waves-long wavelengths & low frequency

The Nature of Light: Wave-Particle duality Light can be modeled as a wave Light waves which are electromagnetic waves consists of changing electric & magnetic fields Light waves may reflect when they meet a mirror, refract when they pass through a lens, or diffract when they pass through a narrow opening. Light can be modeled as a stream of particles Photons- are a particle of light/bundle of energy

The speed of light depends on the medium! Speed of light (c) = 3 x 108 m/s (in a vacuum) Light is the fastest signal in the universe Nothing can travel faster than the speed of light. When light travels through different media, it slows down.

The speed of light depends on the medium! Medium Vacuum 2.997925 Air Speed of light (x 108 m/s) Vacuum 2.997925 Air 2.997047 Ice 2.29 Water 2.25 Quartz 2.05 Glass 1.97 Diamond 1.24

Mirrors Flat mirrors form virtual images by reflection. When you look into a mirror, you see an image of yourself behind the mirror. Virtual image is an image that forms at a point from which light rays appear to come but do not actually come Real image is an image of an object formed by many light rays coming together in a specific location.

Types of Mirrors Curved mirrors can distort images Since the surface is not flat, the line perpendicular to the mirror (normal) points in diff. directions for diff. parts of the mirror. Mirrors that bulge out are called convex mirrors Mirrors that are indented are called concave mirrors Concave mirrors create real images.