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Light as a Wave OBJECTIVES:

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Presentation on theme: "Light as a Wave OBJECTIVES:"— Presentation transcript:

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 Parts of a wave Crest Wavelength Amplitude Origin Trough

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

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 J·s) f = frequency, in units of hertz (hz, sec-1)

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

14 Low Energy High Energy Radiowaves Microwaves Infrared . Ultra-violet X-Rays GammaRays Low Frequency High Frequency 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.


21 Calculating Wavelength of an EM Wave
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).

22 Calculating Wavelength of an EM Wave
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.

23 Examples c = λf or f = c/λ f = 3.0 x 108m/s 4.2 x 10-5 m
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 = x 108m/s 4.2 x 10-5 m = 7.1 x 1012 sec-1 E = hf E = (6.626 x J sec) (7.1 x 1012 sec-1) E = 4.73 x Joules

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