Ch. 16 Sound and Light

Sound  Sound wave: Caused by vibrations and carry energy through a medium.

Properties of Sound 1. Speed of sound -Depends on the medium -The speed of sound in a medium depends on how quickly the particles transmit the motion of the sound waves. -Sound travels faster in solid than in air, because the particles of the medium are closer.

Properties of Sound  Temperature Temperature can change the speed of sound. The higher the temperature the faster the sound wave Particles move faster at high temperatures so they will bump into each other quicker, sending vibrations faster. Rubber is a solid that actually dampens the sound.

Properties of Sound

2. Loudness of sound -Depends on intensity -Intensity of a sound wave describes the rate at which a sound wave transmits energy through something. -Intensity depends on the amplitude of the sound wave and your distance to the source. -Measured in decibels (dB)

Loudness of Sound

Properties of Sound 3. Pitch: -Depends on frequency Pitch is a measure of how high or low a sound is which is determined by the sound waves frequency. Vibrating at a high rate gives a high pitch Measured in hertz (Hz) Vibrating at a low rate gives a low pitch

Pitch

Human hearing ranges Humans can hear sounds at the rate of 20 Hz to 20,000 Hz. Infrasound - any sound that has a frequency below the range of human hearing. Ultrasound - any sound that has a frequency above the range of human hearing.

Human Hearing Ranges

Infrasound

Musical Instruments Instruments produce sound through the vibration of strings, air columns or membranes Musical instruments work because of standing waves. - shorter length = higher pitch - you can change the pitch by changing the length of the standing wave.

Hearing and the Ear - the human ear is a sensitive organ that senses vibration in the air, amplifies them, and then transmits signals to the brain. Ear: Is divided into three regions; outer, middle and inner ear

How you hear 1. Sound is collected and directed into the ear canal by the outer ear. 3. The vibrations then enter into the inner ear. It passes through the hammer, the anvil, and the stirrup. These increase the size of the vibrations. 2. Sound then hits the eardrum causing it to vibrate at the end of the canal. The eardrum is a thin, flat piece of tissue.

How you hear cont. 4. The stirrup strikes a membrane called the basilar membrane in the cochlea to vibrate. Different parts of the basilar membrane vibrate at different frequencies. These vibrations cause tiny hairs to vibrate sending impulses to the brain. ?v=7a2aoZeZhZ8

Light Two models of light 1. Wave Model 2. Particle stream model Two models of light 1. Wave Model 2. Particle stream model

Wave Model - light are transverse electromagnetic waves - these waves can interfere with each other creating dark bands. It can reflect, refract when they pass through a lens and diffract when they pass through a narrow opening

Wave Model

Particle Stream Model - light is energy packets called photons. - a beam of light is a stream of photons. - little bundles of energy with no mass.

Wave and Particle Model

Both models are accepted and used depending on the situation. - light has a dual nature. - can behave as a wave and a particle.

Light energy -amount of energy is proportional to its frequency. - high frequency = high energy

Electromagnetic spectrum

Speed of light (c) - speed of light is a constant and depends on the medium - fastest in a vacuum - 3 x 10 8 m/s or 186,000 mi/s - slower in other mediums because when it hits an atom the light is scattered

Brightness - brightness depends on intensity - intensity- depends on number of photons per second that pass through a given area of space. - intensity decreases with distance. Why?

Electromagnetic Spectrum - spectrum that consists of waves at all possible energies, frequencies, and wavelength. - Goes from longest waves (radio waves) to shortest waves (gamma waves)

Reflection -Light can be thought of as an imaginary line (light ray) -When a light ray hits a rough surface it reflects (bounces off) in different directions.

Reflection - the angle of reflection is equal to the light ray striking the mirror (angle of incidence). This is the Law of Reflection. -When a light ray hits a smooth surface it reflects (bounces off) in one direction.

Law of Reflection - Law of Reflection – the angle of incidence equals the angle of reflection. This explains how flat mirrors work!

Mirrors - flat mirrors form virtual images. - the image that is seen based on the apparent path of the light rays. - the image appears behind the mirror. - this image can not be projected.

Curved mirrors - Convex mirror (curved outward). - makes image smaller - creates a virtual image. - this image can not be projected.

Curved mirrors - Concave mirror (curved inward). - makes image larger - creates a real image. - this image can be projected.

Color - color based on wavelength - color you see is because that is the color reflected off of the object. All other colors are absorbed.

Color