Chap 15 – sound and light waves

• The intensity of a sound wave describes the rate at which a sound wave transmits energy through a given area of the medium.
• Intensity depends on the amplitude of the sound wave as well as your distance from the source of the waves.
• The greater the intensity of a sound, the louder the sound will seem.
• Humans hear sound waves in a limited frequency range.
• Any sound with a frequency below the range of human hearing is known as an infrasound.
• An infrasound is slow vibrations of frequencies lower than 20 Hz.
• Any sound with a frequency above human hearing range is known as an ultrasound.
• An ultrasound is any sound wave with frequencies higher than 20 000 Hz.
• Sonar, sound navigation and ranging, is a system that uses acoustic signals and echo returns to determine the location of objects or to communicate.
• Sonar is used for underwater location.
• A sonar system determines distance by measuring the time it takes for sound waves to be reflected back from a surface.

Waves and Particles

• The two most commonly used models describe light either as a wave or as a stream of particles.
• Light produces interference patterns like water waves.
• Light can be modeled as a wave.
• This model describes light as transverse waves that do not require a medium in which to travel.
• Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields.
• The wave model of light explains much of the observed behavior of light.
• The wave model of light cannot explain some observations.
• Light can be modeled as a stream of particles.
• In the particle model of light, the energy of light is contained in packets called photons.
• A photon is a unit or quantum of light.
• A beam of light is considered to be a stream of photons.
• Photons do not have mass.

The energy in a photon is located in a particular place.

• The brightness of light depends on intensity.
• The quantity that measures the amount of light illuminating a surface is called intensity.
• Intensity is the rate at which energy flows through a given area of space.
• Like the intensity of sound, the intensity of light from a light source decreases as the light spreads out in spherical wave fronts.
• The electromagnetic spectrum consists of light at all possible energies, frequencies, and wavelengths.
• Sunlight contains ultraviolet light.
• The invisible light that lies just beyond violet light falls into the ultraviolet (UV) portion of the spectrum.
• X rays and gamma rays are used in medicine.
• X rays have wavelengths less than 10 –8 m.
• The highest energy electromagnetic waves are gamma rays.
• Infrared light can be felt as warmth.
• Infrared (IR) wavelengths are slightly longer than red light.
• Microwaves are used in cooking and communication.
• Microwaves have wavelengths in the range of centimeters.
• Radio waves are used in communications and radar.
• Radio waves have wavelengths that range from tenths of a meter to millions of meters.
• Air-traffic control towers use radar to determine the locations of aircraft.
• Radar, radio detection and ranging, is a system that uses reflected radio waves to determine the velocity and
  location of objects.

Seeing Colors

• The different wavelengths of visible light correspond to many of the colors that you perceive.
• Objects have color because they reflect certain wavelengths.
• White light from the sun actually contains light from the visible wavelengths of the electromagnetic spectrum.
• Colors may add or subtract to produce other colors.