Wave & Electromagnetic Spectrum Notes

1. Wave & Electromagnetic Spectrum Notes March 12, 2014

2. I.) Properties of Waves • Wave: A periodic disturbance in a solid, liquid or gas as energy is transmitted through a medium ( Waves carry energy b/c they do “work”) *Waves create “wave fronts” (circles) that have the same amount of total energy but as the circles get larger the energy spreads out over a larger area.

3. 1) Mechanical Waves: waves that require a medium through which to travel a) Medium: physical environment in which phenomena occur 1) Example: water, air, Earth b) Almost all waves are mechanical waves, except EM waves

4. 2) Electromagnetic Waves: waves that consist of oscillating electric and magnetic fields, which radiate outward at the speed of light (3.0 x 108 m/s) (Holy Gazoli! That’s fast!) a) Example: visible light, microwaves, etc. b) DO NOT require a medium

5. Fun Wave Vocabulary Ha! Ha! A) Crest: section of the wave that rises above the equilibrium position B) Trough: section which lies below the equilibrium position

6. C) Wavelength: distance between one point on the wave and the nearest point where the wave repeats itself 1) This can be measured from crest-to-crest, trough-to-trough, or from the start of a wave to the start of the next one. 2) Symbol for wavelength is λ

7. D) Amplitude: maximum displacement from the undisturbed position of the medium to the top of a crest.

8. E) Period (T): time required for one wave to complete one full cycle of its motion i.e. The period measures how long it takes for a wave to pass by 1) Example: From its highest point to its lowest and back again 2) Measured in seconds (s)

9. F) Frequency: the number of complete waves that pass a point in a given time. It has the symbol f. 1) SI Units: Hertz (Hz) 2) Hertz units measure the number of vibrations per second ex. 1 vibration per second is 1 Hz, 2 vibrations per second is 2 Hz 3) Period is related to frequency in that the frequency is the inverse of the period Frequency = 1 / period f = 1 / T

10. G) Wave speed 1) The frequency and wavelength are related to one another and to the speed of the wave by the following formula, where “v” is equal to the speed: Speed = Wavelength x Frequency v = f

11. II.) Traveling Through Mediums A) Mechanical waves require a medium in order to travel through 1) Waves are classified by the direction that they travel through the medium a) Transverse Wave: the particles in the medium move perpendicular to the direction wave is traveling 1) Ex: Light waves

12. b) Longitudinal Wave: the particles in the medium move parallel to the direction the wave is traveling 1) Ex: Sound waves

13. C) Surface Wave- occur at the boundary of 2 different mediums (ex. Water and air) • Particles in a surface wave move both perpendicular & parallel to the direction the wave travels • The up/down motion combine w/ the side to side motions to produce a circular motion overall • Ex. Ocean waves

14. 2) Speed and direction of these mechanical waves are affected by the medium they encounter a) Example: Sound waves travel very fast through air, but they travel 3 to 4 times faster under water 1) why so many animals use sound waves to communicate (dolphins) b) They travel even faster in a solid, producing speeds 15 to 20 times faster in rock or metal. Speed of sound waves in types of mediums (slowest to fastest) Gas → Liquid → Solid

15. III.) Doppler Effect: an observed change in the frequency of a wave when the source or observer is moving A) Pitch of a sound (how high or low it is) is determined by the frequency at which the sound waves strike the eardrum 1) When an object that is emitting sound waves (i.e. ambulance) is at rest, the sound waves spread out in circles and anyone who is standing near the object will hear the same pitch

16. 2) When an object that is emitting sound waves (i.e. ambulance) is moving however, the waves are closer together in the direction of the motion. So if one person is standing in the same direction as the motion, the pitch will seem higher than if a person was standing in the opposite direction

17. IV) Wave Interactions A) Reflection: the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through B) Refraction: the bending of waves at an angle when they pass from one medium into another 1) Ex: Spoon in glass of water appears to be broken because the light waves are bending at a different angle when they enter the water versus the air

18. C) Diffraction: The bending of a wave when the wave finds an obstacle or an edge, such as an opening 1) Waves will bend around an object or opening a) Example: hear sounds clearly from classroom only through open door because waves spread out into the space beyond the door

19. D) Interference 1) Constructive Interference: when two waves interact and the resultant wave has a larger amplitude (Part A) 2) Destructive Interference: when two waves interact and the resultant wave has a smaller amplitude (Part B) *HOW LOUD A SOUND IS DEPENDS UPON THE AMPLITUDE OF THE WAVES THAT INTERACT!!

20. Standing wave- can form when a wave is reflected at the boundary of a medium. • Interference occurs b/w the original wave & the reflected wave • Causes wave to vibrate in a stationary pattern (resembles loops) • Looks like wave is standing still but it reality waves are traveling in both directions

21. Standing wave components Nodes- point that has no vibration & separates the loops of a standing wave (lie where the crest of original wave meets the trough of reflected wave Antinodes- point of maximum vibration; form where the crests of the original wave line up w/ the crests of reflected waves

22. Electromagnetic Spectrum NotesI.) Electromagnetic Waves A) What are EM Waves? 1) How are they produced? a) Electric and magnetic fields are constantly changing b) EM waves are produced when electric charges vibrate or accelerate

23. 2) How they travel a) Since electric and magnetic fields are constantly changing, they regenerate each other b) EM waves can travel through a vacuum (empty space) as well as through matter B) Speed of EM waves 1) Michelson (1852-1931) setup an experiment to try and find how fast light travels 2) Speed of light in a vacuum, c=3.00x108m/s

24. II.) Electromagnetic Spectrum A) The Waves of the Spectrum 1) EM spectrum: all of the frequencies or wavelengths of electromagnetic radiation 2) The EM spectrum includes radio waves, microwaves infrared rays, visible light, UV rays, X-rays, and gamma rays.

26. B) Radio Waves -Longest wavelength -Lowest Frequency 1) Radio waves are used in radio & TV technologies, as well as in radar. a) Radio 1) Amplitude modulation (AM) 2) Frequency modulation (FM) b) Radar 1) Send out short bursts of radio waves that bounce off objects & return to receiver

27. C) Microwaves -Shorter wavelength than radio waves -Higher frequency than radio, but lower than infrared 1) Only penetrate food at the surface

28. D) Infrared Waves -Shorter wavelength than microwaves -Higher frequency than microwaves, but lower than redlight 1) Infrared rays are used as a source of heat & to discover areas of heatdifference 2) You can’t see infrared radiation, but your skin feels its warmth

29. E) Visible Light -Each wavelength corresponds to a specific frequency ** Colordetermined by frequency 1) People use visible light to see, help keep them safe, and to communicate with one another.

30. F) UV Rays -Shorter wavelength and higher frequency than violet light 1) UV rays have applications in health and medicine, and in agriculture. a) Helps skin produce Vit. D, can cause sunburn, cancer, and used to kill microorganisms

31. G) X-Rays -Shorter wavelength and higher frequency than UV rays 1) X-rays are used in medicine, industry, and transportation to make pictures of the inside of solid objects. a) X-rays are absorbed by solid objects (teeth, bones) & so solid objects appear white

32. H) Gamma Rays -Shortest wavelength -Highest frequency 1) Gamma rays are used in the medical field to kill cancer cells and to make pictures of the brain & in industrial situations as an inspection tool.