1. Index Unit 03 Electron Configuration Module 01: Light as a Wave Based on the PowerPoints By Mr. Kevin Boudreaux, Angelo State Univerisity U03Mod01 Light as a Wave1

2. Index Module 01: Student Expectations Be able to – define the terms wavelength, frequency, and amplitude. – label the parts of a wave. – calculate the wavelength or frequency using the speed of light equation. – explain interference. – explain diffraction. – explain how we know light behaves like a wave. – state that light behaves as a wave and a particle (dual wave-particle nature). U03Mod01 Light as a Wave2

3. Index Light and Matter We know that both light and electrons have a dual wave-particle nature. – Some properties are best described by a wave model while some properties are best described by a particle nature. U03Mod01 Light as a Wave3

4. Index Electromagnetic Radiation Visible light, infrared radiation, ultraviolet light, radio waves, microwaves, X-rays, and gamma (γ) rays are types of electromagnetic (EM) radiation. Electromagnetic radiation propagates energy using electric and magnetic fields that are perpendicular to each other. U03Mod01 Light as a Wave4

5. Index Frequency, Wavelength, and Amplitude EM radiation behaves in some ways like ocean waves traveling through water. The wave properties of EM radiation can be described by the following three variables: – Wavelength (λ, lambda) – the distance from one wave peak to the next (or trough to trough, or corresponding points) (units of length, m, nm) – Amplitude – the height of the wave measured from the center line (rest position); the intensity or brightness of the light is proportional to the square of the amplitude. – Frequency (ν, nu) – the number of wave peaks that pass by a given point per unit time (units of cycles per second, 1/second, s -1, Hz [Hertz]) U03Mod01 Light as a Wave5

6. Index Frequency, Wavelength, and Amplitude U03Mod01 Light as a Wave6

7. Index The Speed of Light; Relating ν and λ In a vacuum, all EM radiation travels at the speed of light, c or 2.99792458x10 8 m/s. Because the speed of light is constant, frequency and wavelength are inversely proportional to each other: What is different about each type of EM radiation is its wavelength and frequency (and also its energy [more about this later]) Visible light extends from wavelengths of 750 nm (red) to 400 nm (violet); “white light” is a combination of all these wavelengths of radiation. U03Mod01 Light as a Wave7

8. Index The Electromagnetic Spectrum The colors that we see around us results from an object absorbing some wavelengths of visible radiation and reflecting others back to our eyes. White light from the sun can spread out with a prism to form a continuous spectrum, with no breaks in between the colors: Visible light represents only a small portion of the continuum of radiant energy known as the electromagnetic spectrum. – Higher frequency light includes ultraviolet (UV) rays, X-rays, and gamma rays. – Lower frequency light includes infrared (IR) radiation, microwaves, and radio waves. U03Mod01 Light as a Wave8

9. Index The Electromagnetic Spectrum U03Mod01 Light as a Wave9

10. Index The Electromagnetic Spectrum U03Mod01 Light as a Wave10 What radiation has a frequency of 9.6x10 17 Hz? Wavelength of 2.5cm?

11. Index Examples 1) What frequency of radiation has a wavelength of 495 nm? What type of EM radiation is it? U03Mod01 Light as a Wave11

12. Index Examples 2) What is the wavelength of electromagnetic radiation that has a frequency of 6.45 x 10 9 Hz? What type of EM radiation is it? U03Mod01 Light as a Wave12

13. Index Examples 3) What is the wavelength in nanometers of electromagnetic radiation that has a frequency of 5.099x10 14 Hz? What type of EM radiation is it? U03Mod01 Light as a Wave13

14. Index Wave Properties Evidence We know that light and electrons have dual wave-particle nature. Waves can undergo certain phenomenon that also occur with light and electrons. Some of these phenomenon include – Interference – Diffraction U03Mod01 Light as a Wave14

15. Index Constructive and Destructive Interference Waves can interfere with each other constructively or destructively: U03Mod01 Light as a Wave15 Wave amplitudes add Constructive interference Wave amplitudes cancel Destructive interference

16. Index Diffraction A wave bends around an object that is comparable in size to its wavelength, producing a new set of waves in a process called diffraction: A stream of particles, on the other hand, would either be blocked by the barrier, or sail through the opening without being diffracted: U03Mod01 Light as a Wave16

17. Index Diffraction If light strikes a barrier with two slits (with a separation comparable to the wavelength of the light), the light is diffracted through both slits, producing an interference pattern on the other side. This phenomena would be produced by anything which has wave properties, but not by something that has only particle properties. U03Mod01 Light as a Wave17

18. Index Wave Interference Simulation http://phet.colorado.edu/en/simulation/wave- interference http://phet.colorado.edu/en/simulation/wave- interference U03Mod01 Light as a Wave18