Chapter 15

Section 1

 Sound Wave- a longitudinal wave that is caused by vibrations and travels through a material medium  Spread out in all directions away from a source

 Speed of Sound depends on the medium  How fast the medium transfers vibrations  Moves fastest through a liquid or a solid  b/c particles are closer together  Rubber- a solid that is used to sound proof things so waves travel slower

 Loudness is determined by intensity  Intensity is the rate that energy is transferred through a medium  Greater intensity=louder noise  Lower intensity=lower noise

 Relative intensity-comparison of the intensity of a sound w/the intensity of the threshold of hearing  Humans hear loudness on a logarithmic scale  Something that sounds twice as loud is actually 10 times the intensity  Relative intensity is measured in decibels 0 dB quietest sound 120 dB threshold of pain

 Pitch is determined by frequency  High pitch=high frequency=high # of vibrations  Low pitch=low frequency=low # of vibrations

 Humans hear only certain frequencies  Infrasound- slow vibrations of frequencies lower than 20 Hz (humans can’t hear)  Ultrasound- any sound wave with frequencies higher than 20,000 Hz (above what humans can hear)

 A phenomenon that occurs when 2 objects naturally vibrate at the same frequency

Section 15.2

 Thomas Young 1801  Sent a beam of light through 2 small openings and onto a screen. He observed that the light formed a striped pattern similar to water ripples.  Which led to…

 Light consists of waves  Explains why light reflects, deflects, or refracts  Light can consist of particles  Photons- a unit or quantum of light  Explains why blue light can “knock” electrons off a plate

 Speed of light depends on medium  Energy of light is proportional to frequency  Photons carry energy  Greater frequency=greater energy

 Brightness of light depends on intensity  Intensity is what measures the amount of light that illuminates a surface; rate at which energy flows through a given area  Intensity decreases further from the source; light looks dimmer

Increasing Frequency Increasing Energy Increasing Wavelength

 Ultraviolet (UV) light= sunlight, causes cancer and sunburns  X-rays and gamma rays used in medicine  Can treat cancer, look for broken bones, but can kill cells so VERY dangerous

 Infrared light- felt as warmth, comes from sun, used to heat food or map different temps  Microwaves- cooking and communication  Cell phones

 Radio waves- communication and radar; tv and radio signals  Radar- radio detection and ranging, a system that uses reflected radio waves to determine the velocity and location of objects  Radar guns

Section 15.3

 All objects reflect and absorb some light  Light can be modeled like a ray  Light ray- a line in space that matches the direction of the flow of radiant energy  Study of light that behaves like rays is called geometrical optics

 Rough surfaces reflect light in many directions  Reason why rough obj. don’t look shiny b/c light is reflected at all angles  Diffuse reflection

 Smooth surfaces reflect light in 1 direction  Ex: Light hits from one direction and all the light is reflected into a new single direction  Angle of reflection- The angle that the light is reflected off into the new direction  Law of Reflection  The angle of incidence equals the angle of reflection

 Objects have color b/c they reflect certain wavelength  White light from the sun contains (ROY G. BIV) when passed through a prism  Grass reflects wavelengths that correspond to green, and absorbs all other colors  Red roses are red b/c they absorb all colors except for red

 Black is not a color; it is the absence of color  Additive Primary colors- red, blue, green  Put these together and white is formed  From actual light source (ex: printed page)  Subtractive Primary colors- yellow, cyan, and magenta  Combines to form black  From a reflected source (ex: computer screen)  TV’s and computers use this technology

 Form virtual images by reflection  Virtual images- an image that forms at a location from which light rays appear to come but do not actually come  The angle it is reflected at is = to the angle of incidence

 Form virtual images by reflection  Virtual images- an image that forms at a location from which light rays appear to come but do not actually come  The angle it is reflected at is = to the angle of incidence

 Concave mirrors  May produce  Virtual image  Real image- an image of an obj formed by light rays that actually come together at a specific location  At a real image really exist at the point where the image appears

 Telescopes use curved surfaces to focus light

Section 15.4

 Light waves bend when they enter a different medium (pg 513)  Light goes from a medium where the speed is higher to one that lowers the speed, the ray is bent towards the normal (air to glass)  Light goes from a medium that it moves slower to a medium that forces it to move at a higher rate the ray is bent away from the normal (Glass to air)

 Lens- transparent obj that refracts light waves such that they converge or diverge to make an image  Rely on refraction  Can magnify (change in the size of the image of an obj compared to actual size) images  Microscopes, telescopes, and the eye all use refraction and lenses

 Light enters through the cornea  Passes through the pupil  Through the Lens  Muscles adjust the curve of the lenses to focus the image  Image is focused on the Retina  Passed to the rods (dim light) and cones (color vision)  To the brain to be interpreted

 Prism- can separate white light into its component colors (ROY G. BIV)  When light travel through a medium the speed of light is determined by wavelength  Red light is the fastest, Violet is the slowest  Dispersion- light separates into the different colors b/c of wave speeds

 Sun strikes water droplets  Light is dispersed into individual colors as it goes from air to water  Some light is reflected back  Light disperses further as it goes from water back to air  WE see light from many droplets as arcs of colors