Waves

1. Waves

2. Contents • Characteristics of waves • Types of wave • Electromagnetic Spectrum • The 7 Electromagnetic Waves • Uses of Electromagnetic Waves • Sound Waves • Sound Quiz • Ultrasound • Seismic Waves • Colliding: The Andes • Spreading: Mid-Atlantic Ridge • Sliding Past Each Other: San Francisco

3. Characteristics of Waves • Amplitude, a The distance from the middle to either the trough or peak • Wavelength, λ (metres) The distance of one full cycle of a wave • Frequency, f (Hertz, Hz) The number of waves that pass a point in 1 second Waves carry energy from one place to another

4. Types of Wave • Transverse (light, water, strings) Vibrations are at 90° to the direction of wave travel • Longitudinal (sound, slinky spring) Vibrations are along the same direction as wave travel

5. Electromagnetic Spectrum • Electromagnetic waves travel at the speed of light in a vacuum • The electromagnetic spectrum consists of 7 types of em wave:

6. The 7 Electromagnetic Waves Short wavelength Long wavelength Low frequency High frequency

7. Uses of Electromagnetic Waves • Wavelength of the EM spectrum continually changes high frequency = short wavelength high frequency = high energy high energy = more dangerous • Radio Waves(communications) TV and FM radio (short wavelength) Direct line of sight with transmitter (do not diffract) Medium wavelength – travel further because they reflect from layers in the atmosphere

8. Uses of Electromagnetic Waves • Microwaves (cooking and satellite signals) Satellite signals: Frequency of microwaves pass easily through atmosphere and clouds Cooking: microwaves are absorbed by water molecules. These water molecules become heated  heat food Dangers: microwaves are absorbed by living tissue Internal heating will damage or kill cells

9. Uses of Electromagnetic Waves • Infrared Radiation(remote controls, toasters) Any object that radiates heat radiates IR radiation IR is absorbed by all materials and causes heating IR is used for night vision and security cameras as IR is visible in daytime or night-time Police use it to catch criminals, army use it to detect enemy Dangers: damage to cells (burns)

10. Uses of Electromagnetic Waves • Ultraviolet (detect forged bank notes, tanning booths) Darker skin protects UV from penetrating skin tissue deeper under the skin Forged bank notes fluoresce in UV light; real don’t Dangers: overexposure damages surface cells and eyes

11. Uses of Electromagnetic Waves • X Rays(detect bone breaks) X-rays pass through flesh but not dense material like bones Dangers: X-rays damage cells and cause cancers Radiographer precautions include wearing lead aprons and standing behind a lead screen to minimise exposure • Gamma Rays (cause and treat cancers) In high doses, gamma can kill normal cells and cause cancers Gamma can be used to kill mutated cells though too…

12. Sound Waves • How do we hear? Object vibrates  vibrations travel away as a wave Vibrations enter the ear and vibrate a liquid in the inner ear Vibrating liquid affects 1000s of nerves which tell your brain that you can hear a sound

13. Frequency/Pitch (High or Low) Amplitude (dB) (loudness) amplitude amplitude Wavelength (m) Wavelength (m) amplitude amplitude Wavelength (m) Wavelength (m)

14. Sound Quiz The Greek letter  refers to which part of a wave? The distance between two crests of a wave is called the…? Frequency is measured in…? If the amplitude of a sound wave increases, what would you hear? What is the unit of amplitude of a sound wave? Does sound travel through space? Increasing the pitch also increases what? If the amplitude of a light wave increases, what would you see? Which has the highest pitch – a wave with short wavelength or long wavelength? Two people at equal distances from a sound source. One is under water, the other is standing on the ground. Who will hear it first?

15. Ultrasound Ultrasound: sound with very high frequency : frequency above 20kHz - inaudible : high frequency = short wavelength V = f x λ V = wave speed (m/s) f = frequency (Hz) λ = wavelength (m) Wavelength, λ (m)

16. The 4 Uses 1. Industrial Cleaning Ultrasound can be used to clean delicate equipment. Short λ = narrow, focused beam. Vibrations remove dirt effectively by “shaking” dirt loose. No need to dismantle the equipment.

17. The 4 Uses 2. Industrial Quality Control Ultrasound waves can detect cracks inside metals. When a sound wave travels from one substance to another, some waves are reflected back as echoes. The reflected waves (echoes) are detected by a computer... An echo = a flaw in the metal  a crack has formed.

18. The 4 Uses 3. Pre-Natal Scanning X-rays can be used to see inside the body - (unsafe for a baby) Ultrasound can create images and is safer. Passes through new substance (skin, muscle, bone)  waves are reflected as echoes. The reflected waves (echoes) are detected by a computer... which builds up a picture from each echo.

19. The 4 Uses 4. SONAR - Direction and Range • Bats produce ultrasound squeaks •  pick up the reflections using their big ears. • Brain processes the reflected signals into • a mental picture of the surroundings. • Ships use SONAR to detect items on the seabed. • The pattern of the reflections indicates the depth and shapes.

20. Seismic Waves • P waves (primary): • They are longitudinal so they cause the ground to move up and down • They pass through solids and liquids • They go faster through more dense material • S waves (secondary): • They are transverse so they cause the ground to move sideways • They ONLY pass through solids (hint: s wave = solids) • They go faster through more dense material

21. S waves will only travel through a solid P waves travel through the Earth and are refracted when they pass through a medium Seismic Waves The paths of these waves are curved because density is gradually changing Observations: 1) It has a thin crust, 2) it has a semi-fluid mantle where density increases with depth, 3) a core with a liquid outer part and a solid inner part

22. Tectonics • The Earth’s crust is made up of plates of rock like a jigsaw • These plates move slowly as they float on the liquid mantle • This mantle moves slowly by convection currents, caused by the radiation emitted from the Earth’s core • The Earth’s crust is constructed of sedimentary rock layers • These plates meet at boundaries… • … at which plates collide, separate or slide past each other

23. Earth’s Crust Sedimentary rocks settle in layers The oldest rock is at the bottom; the newest at the top Sedimentary rock is often folded or fractured due to pressures:

24. Colliding: The Andes • Oceanic plates are more dense than continental plates • When they collide: oceanic plate is pushed under  earthquake continental plate slides over and crumples  mountains Oceanic plate melts  increased pressure of magma pushes through the crust as a volcano

25. Spreading: Mid-Atlantic Ridge • As tectonic plates move apart, magma rises and sometimes with enough force to produce an underwater volcano • Force causes tidal waves  tsunamis • These cause huge destruction when they reach the land • As the magma rises and cools, underwater mountains form • Evidence for Continental Drift e.g. Atlantic Ocean

26. Sliding Past Each Other: San Francisco • Plates can slide past each other • But when they do, they catch on each other and lurch • This lurch lasts a few seconds but is extremely violent • Violent shaking destroys buildings • Poorer countries suffer worse as they have: 1) overcrowded cities 2) poorly constructed buildings 3) inadequate rescue services

27. Summary • Parts of a wave; transverse (light) and longitudinal (sound) • EM spectrum: radio, microwaves, IR, UV, X-ray, Gamma • Ultrasound has 4 uses • Seismic waves: P (quicker) and S (solid only) waves • Tectonics drift on molten mantle and meet at boundaries • Interaction causes: 1) earthquakes 2) volcanoes 3) mountains 4) trenches 5) ridges 6) evidence for Continental Drift