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# L i g h t !

L i g h t !. Light is a Wave? Objectives: Describe the relationship between the wavelength and frequency of light. Calculate the wavelength and frequency of light using light equations. Light. The study of light led to the development of the quantum mechanical model

## L i g h t !

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1. Light!

2. Light is a Wave? Objectives: Describe the relationship between the wavelength and frequency of light. Calculate the wavelength and frequency of light using light equations.

3. Light • The study of light led to the development of the quantum mechanical model • Light is a type of electromagnetic radiation (energy) • Electromagnetic radiation includes many types: gamma rays, x-rays, ultraviolet light, visible light, infrared, microwaves, and radio waves • Speed of light = 2.998 x 108 m/s; abbreviated “c” • All electromagnetic radiation travels at this same rate when measured in a vacuum

4. The Electromagnetic Spectrum • Visible light is a very small portion of the entire spectrum

5. Waves • Electromagnetic radiation travels in waves (analogous to water waves) • Wavelength = distance from peak to peak • Amplitude = height of the peak (distance from axis to crest or trough) • Frequency = the number of wave peaks that pass in a given time; usually measured per second (1/s or s-1 or Hertz (Hz)) • Speed = rate the waves travel

6. Wavelength and Frequency • Are inversely related • As one goes up the other goes down • Different frequencies of visible light are different colors • There is a wide variety of frequencies • The whole range is called a spectrum

7. Wavelength and Frequency • Electromagnetic radiation travels through space as a wave moving at the speed of light Equation: c = c = speed of light, a constant (2.998 x 108 m/s) (lambda) = wavelength, in meters n (nu) = frequency, in units of hertz (Hz or s-1)

8. Light Problem Solving • Calculate the wavelength of yellow light emitted by a sodium lamp if the frequency of radiation is 5.10 x 1014 Hz. • How far (in kilometers) does starlight travel in 10. minutes? • During a flame test, strontium emits a strong band at 663 nm. What frequency is this light? What is its color? 5-Step Problem Solving/Dimensional Analysis

9. Light is a Particle? Objectives: Describe the relationship between frequency and energy of light. Calculate wavelength, frequency, and/or energy using light equations.

10. Light is a particle? • Energy is quantized. • Light is a form of energy. • Therefore, light must be quantized. • These smallest pieces of light are called photons- particles of electromagnetic energy

11. Light is a particle? • The energy of electromagnetic radiation is directly related to the frequency of the radiation. Equation: E = h E = Energy, units of Joules (kg.m2/s2) h(Planck’s constant) = 6.626x10-34J.s n (nu) = frequency, in units of hertz (Hz or s-1)

12. More Light Problem Solving • What is the wavelength of blue light with a frequency of 8.3 x 1015 Hz? • What is the frequency of red light with a wavelength of 4.2 x 10-5 m? • What is the energy of a photon of each of the above? 5-Step Problem Solving/SF’s/Dimensional Analysis

13. Spectra Objectives: • How do continuous emission spectra and atomic emission spectra differ? • Identify the source of atomic emission spectra. • Explain how the frequencies of emitted light are related to changes in electron energies.

14. Continuous Spectra & Light Continuous Spectra • Sunlight consists of light with a continuous range of wavelengths and frequencies • When sunlight passes through a prism, the different frequencies separate into a continuous spectrum of colors. • Each color blends into the next in order red, orange, yellow, green, blue, and violet (ROYGBV)

15. Light • The color of light depends on its energy, frequency, and wavelength. • Red has the longest wavelength, the lowest frequency, and the lowest energy

16. Light LONG  LOW  LOW E Dec.  Inc.  Inc. E SHORT  HIGH  HIGH E

17. White Light If light is not white… • By heating a gas with electricity, we can get it to give off colors • Passing this light through a prism does something different

18. Atomic Spectra • These are called atomic emission spectra • They are unique to each element, like a fingerprint • Very useful for identifying elements

19. Atomic Emission So how does light relate to electrons??? • When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels. • The light emitted by an electron moving from a higher to lower energy level has a frequency directly related to the energy change of the electron. • Each electron “jump” produces a distinct brightly colored line in the spectrum.

20. Atomic Emission • This spectrum is called an atomic emission spectrum and each element’s spectrum is unique

21. Atomic Emission • Absorption of Energy • Atom absorbs energy from some outside source (e.g. electricity, heat, etc.) • Electron has too much energy to stay in the energy level it is in • Electron moves from lower EL (GROUND STATE) to higher EL (EXCITED STATE)

22. Atomic Emission • Emission of Energy • Electron in an excited state is now UNSTABLE • It loses its excess energy and moves back to a lower energy level • Each “leap” is equal to a an exact frequency

23. Atomic Emission

24. Atomic Emission • The greater the energy transition (“leap”), • the higher the energy released, • the higher the frequency, • the shorter the wavelength • Color in the “visible region” is dependent on this transition. n 6 5 4 3 2 Energy H Violet Teal Red 410nm 486nm 656nm 434nm

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