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Waves and Spectra

Waves and Spectra. In this presentation you will:. explore evidence relating to waves and spectra. calculate frequency, wavelength, and energy, of electromagnetic waves. Next >. Introduction.

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Waves and Spectra

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  1. Waves and Spectra In this presentation you will: • explore evidence relating to waves and spectra • calculate frequency, wavelength, and energy, of electromagnetic waves Next >

  2. Introduction When Rutherford proposed his nuclear atom, it said a lot about the nucleus, but almost nothing about the electrons. When Niels Bohr offered a theory about the electrons just a few years later, he made use of data that had been collected several years earlier. Next >

  3. Electromagnetic Spectra Higher frequency Gamma waves X-rays Ultraviolet Visible light Infrared Microwaves Radio waves Long waves Lower frequency Spectra may not initially seem to have much to do with atoms, but the connection should become clear later on. The visible light spectra had been investigated by Isaac Newton. Lots of other electromagnetic waves had been discovered, and placed on the spectrum. Next >

  4. Wavelength (m) Features of Electromagnetic Waves The wavelength is the distance in meters between waves. It is usually measured as the distance from one crest to the next. However, the wavelength will be the same, from any point of a wave, to the same point on the next wave. Next >

  5. Lower frequency wave One second Higher frequency wave Features of Electromagnetic Waves The frequency of a wave is the number of wavelengths produced per second, or the number of waves that pass a certain point in one second. Frequency is measured in hertz (Hz). The greater the frequency of a wave, the shorter its wavelength. Next >

  6. Speed of Electromagnetic Waves Electromagnetic waves While electromagnetic waves can be categorized by their frequency or wavelength, they cannot be categorized by their speed. Speed = 3  108 m/s This is because all electromagnetic waves (including light) travel at the same speed. This speed (or velocity, as it is traveling in a straight line) in a vacuum is 3  108 m/s. Next >

  7. Speed, Wavelength, and Frequency Speed, wavelength, and frequency, are related by the equation: c = f λ Where: c is the speed of an electromagnetic wave in m/s(a constant) λ is the wavelength in m f is the frequency in Hz Hz is hertz, where one hertz is one wavelength per second. Next >

  8. Question 1 A light wave has a wavelength of 1 micrometer. What is its frequency? The speed of light is c = 3 × 108 m/s. Give your answer as a number in THz (terahertz). Next >

  9. Question 1 A light wave has a wavelength of 1 micrometer. What is its frequency? The speed of light is c = 3 × 108 m/s. c = f λ 3 × 108 c f = = 3 × 1014 Hz f = 1 × 10-6 λ f = 300 × 1012 Hz = 300 THz Give your answer as a number in THz (terahertz). 300 (THz) Next >

  10. Question 2 What is the effect on the wavelength if the frequency of a wave is doubled? A) The wavelength will not change. B) The wavelength will double. C) The wavelength will half. D) The wavelength will be four times larger. Next >

  11. Question 2 What is the effect on the wavelength if the frequency of a wave is doubled? A) The wavelength will not change. B) The wavelength will double. C) The wavelength will half. D) The wavelength will be four times larger. Next >

  12. Question 3 The frequency of an electromagnetic wave measures 20 GHz. What is its wavelength? The speed of an electromagnetic wave is c = 3 × 108 m/s. Give your answer as a number in mm. Next >

  13. Question 3 The frequency of an electromagnetic wave measures 20 GHz. What is its wavelength? The speed of an electromagnetic wave is c = 3 × 108 m/s. c = f λ 3 × 108 c λ = = 15 × 10-3 m = 15 mm λ = 20 × 109 f Give your answer as a number in mm. 15 (mm) Next >

  14. Energy and Frequency Shorter wavelength Higher frequency Gamma waves X-rays Ultraviolet Visible light Infrared Microwaves Radio waves Long waves Longer wavelength Lower frequency If the electromagnetic spectrum is looked at in terms of the danger of the various waves, a pattern can be seen. Gamma waves are the most dangerous and radio waves are the least dangerous. Next >

  15. Energy and Frequency Shorter wavelength Higher frequency Gamma waves X-rays Ultraviolet Visible light Infrared Microwaves Radio waves Long waves Longer wavelength Lower frequency Waves of a higher frequency, and therefore shorter wavelength, are the most dangerous. The more dangerous waves must have more energy. Next >

  16. Max Planck and Albert Einstein In 1900, Max Planck realized that, in certain circumstances, an electromagnetic wave behaved in a similar way to a particle, even though it was a wave. A particle of light was called a photon. E = h f Einstein investigated these photons, and realized that their energy was directly proportional to their frequency. Next >

  17. Max Planck and Albert Einstein The relationship was given by: E = h f Where: E is the energy in joules (J) f is the frequency in Hz h is Planck’s constant Einstein related the energy of a particle to its frequency in the electromagnetic spectrum. The higher its frequency, the greater its energy. Next >

  18. Question 4 What is a ‘particle’ of light called? A) Proton B) Pronoun C) Phonon D) Photon Next >

  19. Question 4 What is a ‘particle’ of light called? A) Proton B) Pronoun C) Phonon D) Photon Next >

  20. Question 5 In the formula E = h f, what doesh represent? A) Planck’s constant B) The wavelength C) The frequency D) The speed of light Next >

  21. Question 5 In the formula E = h f, what doesh represent? A) Planck’s constant B) The wavelength C) The frequency D) The speed of light Next >

  22. Quantum of Energy Planck’s constant has a value of 6.63  10-34 J s. The energy that a single photon carries, is referred to as a quantum of energy. c = f λ E = h f Since h is a constant, this quantum of energy totally depends upon the frequency. h c E = It’s possible to combine the two formulas. λ Replacing f gives an alternative form to the relationship. Next >

  23. Types of Spectra The spectra we have looked at, is a continuous spectra. Another type of spectra is an emission spectra. This is produced by heating a substance until it glows, and then examining the spectra of the light it emits. This is an emission spectra of hydrogen. Next >

  24. Emission Spectra The emission spectra is also known as a line spectra. This hydrogen spectra shows five lines, each representing a discrete frequency of light. Each line is of a different color, since it has a different frequency (and wavelength). Four lines are in the visible light region, one is in the UV region. Next >

  25. h c 6.63  10-34  3  108 E = E = J λ 656  10-9 Quantum of Energy In the hydrogen emission spectra, the red line has a wavelength of 656 nm. The energy can be calculated: 656 nm Planck’s constant, h = 6.63  10-34 J s Speed of light, c = 3  108 m/s E = 3.03  10-19 J Next >

  26. h c 6.63  10-34  3  108 E = E = J λ 434  10-9 Quantum of Energy Now consider the energy for particles emitted in the blue line, with a wavelength of 434 nm. 656 nm 434 nm 3.03  10-19 J 4.58  10-19 J E = 4.58  10-19 J This shows a greater energy for the particles emitted at a higher frequency (shorter wavelength). Next >

  27. Other Emission Spectra It’s not just hydrogen that gives an emission spectra. Sodium Mercury Neon Next >

  28. Absorption Spectra There is another type of line spectra, called an absorption spectra. If a continuous spectra is passed through a gas, then the result is as shown. Once again, the example is hydrogen. This time there is a series of black bands or gaps in the continuous spectra. The hydrogen gas absorbs the light at five discrete frequencies. Next >

  29. Absorption Spectra The gap in the red area can be shown to correspond to a wavelength of 656 nm. The absorption spectra lines of hydrogen, correspond with those in its emission spectra. 656 nm This means the frequencies at which it emits energy, are identical to those when it absorbs energy. Next >

  30. Question 6 Name the types of spectra. 1 2 3 A) 1 absorption, 2 line, 3 continuous B) 1 continuous, 2 absorption, 3 emission C) 1 continuous, 2 line, 3 absorption Next >

  31. Question 6 Name the types of spectra. 1 2 3 A) 1 absorption, 2 line, 3 continuous B) 1 continuous, 2 absorption, 3 emission C) 1 continuous, 2 line, 3 absorption Next >

  32. Summary In this presentation you have seen: • the different types of spectra and how they arrange waves in order of frequency, wavelength and energy • how to calculate wavelength and frequency using the speed of light • how to calculate energy of a particle from Planck’s constant and the speed of light End >

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