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Unit C: Electromagnetic Energy

Unit C: Electromagnetic Energy. Chapter 2: Electromagnetic spectrum. 2.1- Electromagnetic Radiation (EMR). Defined as a wave with a changing electric and magnetic field perpendicular (90°) to each other EMR is all the energy from the sun.

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Unit C: Electromagnetic Energy

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  1. Unit C: Electromagnetic Energy Chapter 2: Electromagnetic spectrum

  2. 2.1- Electromagnetic Radiation (EMR) • Defined as a wave with a changing electric and magnetic field perpendicular (90°) to each other • EMR is all the energy from the sun. • Waves transmit energy from one location to another through vibrations; in EMR the fields vibrate and energy is transferred in space.

  3. EMR waves

  4. 1) Wave terminology • Transverse- vibrations are perpendicular to the motion of wave. • Longitudinal- vibrations are in the same direction of motion. • Crest- the highest point of the wave. • Trough- the lowest point of the wave. • Cycle- one complete vibration (1 crest and 1 trough). • Wavelength (λ) – length of 1 cycle. • Frequency ()- number of cycles per second.

  5. Types of Waves Longitudinal waves JAVA APPLET Transverse Wave and Longitudinal Waves Transverse Wave Transverse Waves-1

  6. 2) Universal Wave equation • Applies to all types of waves; speed is always the speed of light (c = 3.00 x108 m/s). • Used to calculate speed, wavelength or frequency. Where v = speed (m/s)  = wavelength (m)  = frequency (Hz)

  7. Example • An excited atom in a neon sign emits EMR with a wavelength of 6.4 x10-7 m. 1) Calculate the frequency. 2) If the sign is 25.0m from a person, how long will it take for light to reach them?

  8. 3) The Electromagnetic spectrum • The complete range of EMR; arranged using  and  . • Classifying the different types is done using: - Nature of the source. - Energy transmitted - Effect on living tissue. Electromagnetic Spectrum

  9. a) Radio waves • Lowest frequency; highest  • Produced by electrons vibrating in circuits; used for communications. • Can not penetrate metal = antennas. • Types: • ELF ( emitted from circuits at 60Hz) • Waves with  = 4m used for MRI’s. • Do not harm body tissue (low energy) radio waves

  10. b) Microwaves • Used for radar (higher  ), satellites and cooking food (lower  ). • Transmit more energy than radio waves;  = 100 GHz. • Effects: • Living tissue has a high % of water; can harm tissues (especially eye lenses).

  11. c) Infrared radiation (IR) • Causes molecules to vibrate = heat. • Waves with a  = 4.3 x1011 Hz • Skin sensors can detect IR using heat receptors; energy is not seen, it is felt. • Used for PDA’s; the IR is “beamed” to the device using a transmitter; received using a receiver (Wii).

  12. d) Visible Light • Complete range of all colors that can be seen by the eye (ROYGBIV). • Vision limits= violet (= 400 nm) and Red (= 700nm). • Visible light is emitted by things that are hot. • Light is not a wave, but a photon (packet of energy); the higher  = lower Energy.

  13. Photosynthesis • Plants use visible light photons and absorb the energy in order to grow. • Photon is absorbed by chlorophyll and the energy is used to convert Carbon dioxide and water to sugar.

  14. e) Ultraviolet (UV) Radiation • Emitted by very hot objects;  = 1 x1018 Hz. • Photons have more energy than visible light; this can cause cancer/premature aging. • Divided into 3 types: • UVA/B- high energy; protect using sunglasses • UVC- absorbed by ozone layer (stratosphere); causes DNA mutations that can lead to death (ionizing radiation).

  15. f) X-rays • High energy waves;  = 1021. • Created when electrons strike metal; produced using a high voltage tube. • Penetrate skin easily (dark), are absorbed into bones (white) = dark and light image. • Powerful form of ionizing radiation; cause deadly DNA mutations. • ALARA – keeping the radiation exposure as low/short as possible.

  16. g) Gamma Radiation • Highest energy radiation; shortest . • Are radioactive photons (from radioactive decay). • Are ionizing radiation; cause DNA mutations very quickly. Radioactivity

  17. 2.2) Astronomy • The science of objects/phenomena that originate outside Earth’s atmosphere. • Stars emit EMR; we can study them using Telescopes. • The closest star to earth is the sun: Under high temperatures (15 000 000 °C) and pressures nuclei fuse together forming 1 nucleus (nuclear fusion). • Nuclear fusion results in the release of a helium nucleus and gamma photons. Sun

  18. a) EMR emitted by the Sun • Then energy from the photon released in nuclear fusion is absorbed and then reemitted. • Made up of Visible light and IR (temperature at surface = 6000°C) • Emits all EMR; hottest parts (core) emits the highest energy EMR. • Solar flares = eruption in sun’s atmosphere due to magnetic fields; emits mostly X-rays and gamma rays.

  19. b) Earth’s atmosphere • Atmosphere filters all EMR except radio waves and EMR close to the visible spectrum from reaching earth. • Gases that absorb radiation: • Oxygen/ozone = UV radiation • H20/CH4/ CO2 = IR • Mesosphere/ionosphere atoms = X-rays and gamma rays. • Electrons = long wave radio waves. Earth

  20. c) Properties of light • Refraction = bending of light. • Reflection = wave bounces off surface. • Polarization = forcing a wave to vibrate (move) in only 1 direction • Diffraction = bending of a wave as it passes through an object/opening. Refraction and Diffraction

  21. Reflection Diffraction Polarization Refraction

  22. d) Telescopes • EMR emitted from the sun provides information; the first telescope was invented 400 years ago and studies EMR. 3 types of telescopes: • Refracting • Reflecting • Multiwavelength Telescopes

  23. 1) Refracting Telescopes • First developed by Galileo • Uses 2 lenses (concave and convex). • Problems: • Quality of glass is very low. • Opening was too small. • Diffraction caused errors in distance to the sources of EMR. Galileo Galilei

  24. 2) Reflecting Telescopes • Uses a curved mirror that focuses using reflection. • Advantages: • Mirrors do not separate light into colors like lenses do = higher resolution. • Large openings = less diffraction. • Mirror can be supported from underneath; maintains shape. • Used to gather Visible light, IR and UV radiation.

  25. c) Multiwavelength telescopes • Advanced reflecting telescopes that are at high altitudes or orbiting the earth. • Gathers as many types of EMR as possible; differences in telescopes based on type of radiation absorbed. • Radio waves = huge dish (largest ); produce lots of diffraction--- use many radio telescopes to collect data. • X-rays = Chandra X-ray telescope uses 2 mirrors and an X-ray.

  26. d) Analyzing starlight • Scientists use prisms or diffraction gratings to analyze the EMR into wavelengths. • Objects at 6000°C emit mostly visible light; create a “rainbow” or colors called the continuous spectrum. • Beyond the sun, the spectrum is not continuous but has dark lines where radiation has been absorbed = Dark-line/absorption spectrum.

  27. spectrums neon lights • Start spectrums can be used to determine what gases are in the star. • When current is forced through a gas, the gas emits wavelengths = emission or bright-line spectrum. • Spectra are analyzed using a spectroscope/spectrometer; a diffraction grating attached to a device that calculates .

  28. Rainbows

  29. e) Doppler Shift • Doppler effect: the frequency of sound changes as the source moves toward/away from the observer. • Towards = higher frequency. • Away = Lower frequency. • The same effect happens with EMR: • Blue shift = higher frequencies, moves towards. • Red shift = lower frequencies; moves away.

  30. sound demo Doppler Effect

  31. f) Life Cycle of a Star Aliens • Formation of a Star • Space has some gases and dust in it • Over millions of years, gravitational forces between the dust and gas result in NEBULA, large highly compressed clouds • Gravitational forces continue and stars are born in NEBULAE

  32. 2. STABLE PHASE OF A STAR • Called Main Sequence Star • Gravity created heat and pressure to fuel fusion reactions • Larger stars have shorter lifespans: Fg big  pressure big  more heat rapid fusion rxns  run out of fuel

  33. 3. Death of a Star run out of Hydrogen their main fuel Gravity causes core to collapse Heat is generated causing expansion of outer core Expansion leads to cooling The cooler larger star is called a RED GIANT

  34. Medium Sized Stars (up to 1.5x sun) become WHITE DWARF a stable star with no fuel that radiates left over heat Giant Stars SUPERNOVA results in a BLACKHOLE, an area so dense with such strong gravity not even light can escape After the Red Giant Black Holes Huge Sized Stars (1.5 – 3x sun) • Massive short lived explosion called SUPERNOVA blows away outer layer of star • NEUTRON STAR results (Pulsar is one star that emits radio waves)

  35. Supernova Giantstars Black Hole Main Sequence Star Neutron Star (eg Pulsar) Nebula Red Giant Supernova Hugestars White Dwarf Summary: Life Cycle of a Star Medium stars Life Cycle of Stars

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