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# Week 3- Electromagnetic waves and SPECTRUm

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1. Week 3- Electromagnetic waves and SPECTRUm

2. objectives • Recap wave characteristics. • Learn about Electromagnetic waves and spectrum.

3. Recap - Challenge • Define and describe frequency and period related? • Define and describe how velocity and wave length, and frequency are related? • A tuning fork has a frequency of 280 Hertz and the wavelength of the sound produced is 1.5 meters. Calculate the velocity of the wave. • A wave is moving toward shore with a velocity of 5.0 m/s. If its frequency is 2.5 hertz, what is its wavelength?

4. Amplitude and Energy • Amplitude – the energy carried by a wave or how high the wave is; related to the amount of energy • For compressional waves it’s the amount of compression in the wave • Example: The higher the wave, the more energy (THINK on ocean waves)

5. ELECTROMAGNETIC WAVES • They travel as vibrations in electrical and magnetic fields. • Have some magnetic and some electrical properties to them.

6. When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other. • RESULT-An electromagnetic wave.

7. Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light). At this speed they can go around the world 8 times in one second. Speed of electromagnetic waves in vaccum: 3 * 108 m/s

8. Waves or Particles? • Electromagnetic radiation has properties of waves but also can be thought of as a stream of particles. • Example: Light • Light as a wave: Light behaves as a transverse wave which we can filter using polarized lenses. • Light as particles (photons): When directed at a substance light can knock electrons off of a substance (Photoelectric effect)

9. GAMMA RAYS • Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency ULTRAVIOLET RAYS RADIO WAVES INFRARED RAYS X-RAYS MICROWAVES VISIBLE LIGHT

10. The Electromagnetic Spectrum The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

11. Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. RedOrangeYellowGreenBlueIndigoViolet ROY G BIV

12. FrequencyRanges ofVisibleLight Red light has a frequency of roughly 4.3 × 1014 Hz, and a wavelength of about 7.0 × 10­7 m (700nm). Violet light, at the other end of the visible range, has nearly double the frequency—7.5 × 1014 Hz—and (since the speed of light is the same in either case) just over half the wavelength— 4.0 × 10­7 m (400nm).

13. The radiation to which our eyes are most sensitive has a wavelength near the middle of this range, at about 5.5 x 10-7m (550 nm), in the yellow-green region of the spectrum.

14. It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

15. The product of wavelength and frequency always equals the speed of light. C = λν • Why does this make sense? • NOTE: c is a constant value= 3.00 x 108 m/s

16. PROBLEMS • Calculate the wavelength of yellow light emitted from a sodium lamp if the frequency is 5.10 x 1014 Hz (5.10 x 1014 s-1) List the known infoList the unknown c = 3.00 x 1010 cm/swavelength (λ) = ? cm Frequency (v) = 5.10 x 1014 s-1 C = λvλ = c v λ = 3.00 x 1010 cm/s = 5.88 x 10-5 cm 5.10 x 1014 s-1

17. YOUR TURN 1- What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1? 2- What frequency is radiation with a wavelength of 5.00 x 10-6 cm? In what region of the electromagnetic spectrum is this radiation? 3. What is the frequency of red light of wavelength 632.9 nm?

18. Homework • Watch and learn: https://www.youtube.com/watch?v=hXe7EVv1y0Q • Memorize Electromagnetic spectrum. (Types of waves, frequency and wavelength ranges) • Solve the problem sheets provided in the class. • In case you lost this. You can print here: