Sound and Light

1. Sound and Light

2. Sound and its Characteristics • Sound is an effect of mechanical radiation. • Radiation is the movement of energy from one place to another.

3. How sound travels • Mechanical radiation requires a material medium to pass the energy from one place to another. This causes vibrations which disturb surrounding molecules (for example in the air) and making radiating waves that produce sound energy.

4. Most sounds go through gas (atmosphere). • The warmer the air, the greater the speed of sound. • On a mountain, the air is thinner and does not contain as many molecules as the air in the valley. Therefore, sound does not travel as fast on a mountain.

5. Sound travels faster and farther on liquids than through gases. (When you are in the ocean you can hear people talking from far away.) • It travels faster through a solid.

6. Soft solids, such as cork, rubber, felt, and cotton, are poor conductors of sound because they tend to absorb sound waves rather than conduct them. • They are poor conductors but great for sound proofing.

7. Sound cannot travel in a vacuum. If there are no molecules to vibrate, there is no sound.

8. Compression • When a string vibrates it moves back and forth rapidly. As it moves forward, it pushes against the molecules of air in front of it and presses them closer together. • The space in which the molecules are pressed closer together is called a compression.

9. Rarefraction • As the string moves backward, it leaves a space with fewer molecules in it, and these molecules spread farther apart. The space in which the molecules are spread farther apart is called a rarefaction.

10. One compression and one rarefaction together make up one complete sound wave, vibration or cycle (ciclo). • As an object vibrates back and forth, it produces continuous cycles of compression and rarefraction.

11. The Nature of Waves • What is a wave? • A wave is a repeating disturbance or movement that transfers energy through matter or space

12. What is wavelength? Wavelength is a measure of distance, so the units for wavelength are always distance units, such as meter, centimeters, millimeters, etc.

13. What is wave frequency? Frequency is the number of waves that pass through a point in one second. The unit for frequency is waves per second or Hertz (Hz). One Hz = One wave per second.

14. Wavelength and frequency are inversely related. The smaller the wavelength, the more times it will pass through a point in one second. The larger the wavelength, the fewer times it will pass through a point in one second.

15. What are mechanical waves? Mechanical waves are waves which require a medium. A medium is a form of matter through which the wave travels (such as water, air, glass, etc.) Waves such as light, x-rays, and other forms of radiation do not require a medium. What are the two kinds of mechanical waves? Transverse Waves In a transverse wave the matter in the wave moves up and down at a right angle to the direction of the wave

16. What are the parts of a wave? Transverse wave The crest is the highest point on a transverse wave. The trough is the lowest point on a transverse wave. The rest position of the wave is called the node or nodal line. The wavelength is the distance from one point on the wave to the next corresponding adjacent point.

17. Examples of transverse waves would be light waves, seismic waves (generated by an earthquake) or any other type of electromagnetic wave (x-rays, radiowaves, microwaves).

18. What are mechanical waves? Mechanical waves are waves which require a medium. A medium is a form of matter through which the wave travels (such as water, air, glass, etc.) Waves such as light, x-rays, and other forms of radiation do not require a medium. What are the two kinds of mechanical waves? Longitudinal Waves (Compression Waves) In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave

19. Compressional Longitudinal wave On a compressional wave the area squeezed together is called the compression. The areas spread out are called the rarefaction. The wavelength is the distance from the center of one compression to the center of the next compression.

20. Longitudinal waves are waves that have vibrations along or parallel to their direction of travel. Examples of longitudinal waves are sound waves, tsunami waves, vibrations in gases, ultra sounds, earthquake P-waves.

21. Differences in Sound • Pitch- The faster an object vibrates, the higher the sound’s frequency or pitch. • Subsonic- are frequencies that are lower than a human can hear • Supersonic/ultrasonic frequencies- are too high for a human to hear

22. Can you hear this?

23. Frequency • Sound is measured by the number of cycles produced per second. This number is its frequency. • Frequency is measured in hertz (Hz). • 1 Hz is = 1 cycle

24. Extremely low frequencies can cause physical and chemical reactions. Ex. Ultrasonic sound waves can: • kill bacteria, insects, and pests • Control and operate automatic garage doors

25. Intensity • Intensity is the loudness/softness of a sound. • It does not have to do with pitch.

26. Amplitude • Amplitude -the distance the object is vibrating • The greater the amplitude, the more energy the sound wave has

27. Decibel • The unit of measurement used to measure intensity is decibels.

28. Doppler Effect • The compression and lengthening of a sound wave will change the frequency of the sound. This is known as the Doppler Effect

29. Sound is made when something vibrates. • The vibration disturbs the air around it. • This makes changes in air pressure. • These changes in air pressure move through the air as sound waves.

30. The sound waves cause pressure changes against our ear drum sending nerve impulses to our brain.

31. This is similar to throwing a rock into a pond. Air molecules ripple through the air in sound waves like water waves rippling across a pond.

32. Sound travels through different media. We hear sound which usually travels through air. Sound travels through other media as well, such as water and various solids. Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas. The denser the medium, the faster sound will travel. The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound.

33. What is echolocation?

35. The Voice • At the top of your trachea (tráquea) is your larynx (laringe). Above it are 2 thin bands called your vocal chords. Air pushed through your lungs cause them to vibrate.

36. Musical Instruments Sounds produced by regular vibrations are called music.

37. Light • Visible light is a form ofElectromagnetic Radiation

38. Radiation is the movement of energy from one place to another.

39. 3 Types • Particle Radiation – Given off by decaying atoms, fast moving subatomic particles • Mechanical Radiation – Sound Waves • Electromagnetic Radiation – Light Waves, radio waves, x-rays

40. Electromagnetic waves, speed, wavelength, and frequency Low frequency, long wavelengths High frequency, short wavelengths

41. The only electromagnetic wave that we can see is visible light.

42. Most detectors of electromagnetic radiation are antennas or telescopes.

43. Electric fields + Magnetic fields = Electromagnetic Radiation

44. Electromagnetic radiation can travel through a vacuum and air. • It does not need a medium like mechanical energy (sound).

45. Electromagnetic waves travel at the same speed but differ in wavelength and frequency. • All electromagnetic waves, including light, travel in a vacuum at the same speed (almost 300,000 km/second)

46. Waves with Long Wavelengths and Low Frequencies • Infrared rays are a band of invisible waves that we feel as heat. • Much of the sun’s energy comes to us in this form. • Example of thermal infrared FLIR Camera used by firefighters

47. Infrared • infrared radiation is heat or thermal radiation. • This is radiation produced by the movement of molecules in an object. The higher the temperature, the more the molecules move and the more infrared radiation they produce.

48. Infrared • Any object which has a temperature anything above absolute zero, shows in the infrared. • Absolute zero is the temperature where all atomic motion stops. • Absolute 0 is 0 degrees Kelvin = -459.67 degrees Fahrenheit and -273.15 degrees Celsius

49. Infrared • Even cold objects like ice give off infrared. • When an object is not hot enough to radiate visible light, it will let off most of its energy in infrared.

50. Microwaves • Next to infrared rays are microwaves. • Microwave energy is produced by MASERs. M – Microwave A - Amplification S - by Stimulated E - Emission R - of Radiation