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Light as a Wave

Light as a Wave. OBJECTIVES: Describe the relationship between the wavelength and frequency of light. Electrons and Light. After Bohr’s model, the mystery of the atom was the nature of the electron cloud.

xavier-nielsen
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Light as a Wave

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  1. Light as a Wave • OBJECTIVES: • Describe the relationship between the wavelength and frequency of light.

  2. Electrons and Light • After Bohr’s model, the mystery of the atom was the nature of the electron cloud. • The study of light – particularly the wave nature of light – played a critical role in probing the nature of the electron cloud.

  3. Light and Energy are Linked • Energy travels through space as light waves. • These Light waves are known as Electromagnetic Radiation (EMR) • EMR – defined as a form of energy that exhibits wavelike behavior as it travels trough space.

  4. Types of EMR • Visible Light is one type of EMR • Others include x-rays, microwaves, radiowaves, gamma rays, ultraviolet waves, infrared waves. • All electromagnetic radiation travels at this same rate. • This rate is the speed of light (c) • c = 3.0 x 108 m/sec

  5. - Page 139 “R O Y G B I V”

  6. Basic Properties of Waves • Wavelength (λ- lambda) – distance between two crests of a wave. Units are usually meters. • Frequency (f or (nu))- the number of wave cycles that pass a given point per unit time (usually seconds) • Units are sec-1 = Hertz

  7. Crest Wavelength Amplitude Trough Parts of a wave Origin

  8. Wavelength and Frequency • Are inversely related • As one goes up the other goes down. • c = or c = f c = speed of light = 3.0 x 108m/s

  9. As frequency decreases, wavelength increases. • As frequency increases, the wavelength decreases.

  10. Different frequencies of light are different colors of light. • There is a wide variety of frequencies • The whole range is called a spectrum

  11. R O Y G. B I V red orange yellow green blue indigo violet EM Spectrum HIGH ENERGY LOW ENERGY

  12. The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation. Equation:E = hf E = Energy, in units of Joules (kg·m2/s2) (Joule is the metric unit of energy) h = Planck’s constant (6.626 x 10-34 J·s) f = frequency, in units of hertz (hz, sec-1)

  13. Low ENERGY Waves = Long Wavelength = Low Frequency Wavelength Table High ENERGY Waves = Short Wavelength = High Frequency

  14. Low Frequency High Frequency Low Energy High Energy X-Rays Radiowaves Microwaves Ultra-violet GammaRays Infrared . Long Wavelength Short Wavelength Visible Light

  15. Behavior of Light That Supports Wave Theory • Reflection — Waves rebound from a collision with an even substance at the same angle which they approached it.

  16. Refraction — Waves change speed when they enter a new medium (from air to water).

  17. Refraction explains how a prism separates the colors that make up white light. Each color will refract (or bend) to different degrees based on its characteristic wavelength

  18. Diffraction— Waves can interfere with other waves • They create diffraction patterns • Constructive interference—occurs when a crest meets a crest or a trough meets a trough

  19. Destructive interference—occurs when a crest meets a trough For light waves, you see darkness with destructive interference.

  20. Electrons in Atoms: Basic Concepts Topic 9 Calculating Wavelength of an EM Wave • Microwaves are used to transmit information. • What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz? • Solve the equation relating the speed, frequency, and wavelength of an electromagnetic wave for wavelength (λ).

  21. Electrons in Atoms: Basic Concepts Topic 9 Calculating Wavelength of an EM Wave • Substitute c and the microwave’s frequency, n, into the equation. Note that hertz is equivalent to 1/s or s–1.

  22. Examples 2) What is the frequency of red light with a wavelength of 4.2 x 10-5 m? 3) What is the energy of the photon above? c = λf or f = c/λ f = 3.0 x 108m/s 4.2 x 10-5 m = 7.1 x 1012 sec-1 E = hf E = (6.626 x 10-34 J sec) (7.1 x 1012 sec-1) E = 4.73 x 10-21 Joules

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