Sound and Light

1. Sound and Light Chapter 15

2. Sound Section 1

3. Properties of Sound • 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

4. Properties… • 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

5. Properties… • Loudness is determined by intensity • Intensity is the rate that energy is transferred through a medium • Greater intensity=louder noise • Lower intensity=lower noise

6. Properties… • 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

7. Properties… • Pitch is determined by frequency • High pitch=high frequency=high # of vibrations • Low pitch=low frequency=low # of vibrations

8. Properties • 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)

9. Resonance • A phenomenon that occurs when 2 objects naturally vibrate at the same frequency

10. The Nature of Light Section 15.2

11. Early Thoughts • 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…

12. Light Properties • 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

13. Light Properties • Speed of light depends on medium • Energy of light is proportional to frequency • Photons carry energy • Greater frequency=greater energy

14. Light Properties • 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

15. Increasing Frequency Increasing Energy IncreasingWavelength

16. Electromagnetic Spectrum • 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

17. Electromagnetic Spectrum • Infrared light- felt as warmth, comes from sun, used to heat food or map different temps • Microwaves- cooking and communication • Cell phones

18. Electromagnetic Spectrum • 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

19. Reflection and Color Section 15.3

20. Reflection of Light • 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

21. Reflection and Color • 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

22. Reflection and Color • 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

24. Seeing Colors • 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

26. Seeing Colors • 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

27. Mirrors • 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

28. Mirrors • 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

29. Mirrors • 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

30. Mirrors • Telescopes use curved surfaces to focus light

31. Refraction, Lenses, and Prism Section 15.4

32. Refraction of Light • 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)

33. Lenses • 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

34. The Eye • 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

35. Dispersion and Prisms • 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

36. Rainbows • 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