1. 5.1 T HE N ATURE OF L IGHT Chemistry Ms. Pollock 2013 - 2014

2. I NTRODUCTION Understanding of Rutherford’s model requires understanding of light 1600s debate about how light travels Isaac Newton – light beam of particles Christian Huygens – light wave of energy Neither hypothesis dominant until 1864 wave model of light (James Clerk Maxwell) accepted by many Relationship between magnetism and electricity Debate renewed by Max Planck sixty years later

3. I NTRODUCTION Above left: Newton; above right: Huygens; below left: Planck; below right: Maxwell

4. T HE W AVE F ORM OF E NERGY Wave model of electromagnetic radiation similar to waves on rope Moving rope up and down with one end secured, motion passed from one part of rope to next Rope gains wave shape

5. T HE W AVE F ORM OF E NERGY Crest – highest point of wave Trough – lowest point of wave No horizontal motion of particles Wavelength – distance from one crest to the next crest; symbol

6. T HE W AVE F ORM OF E NERGY Amplitude – maximum height of wave Velocity – distance traveled by wave in one second (unit m/s, symbol ) Frequency – number of cycles that pass a given point per unit of time (unit 1/s or s -1 ) Hertz – wave cycles per second (symbol  )

7. T HE W AVE F ORM OF E NERGY Velocity, wavelength and frequency related =  Velocity = frequency X wavelength What is the wavelength of a water wave if its velocity is 5.0 m/s and its frequency is 2.0 s -1 ? = = 5.0 m/s = 2.5 meters  2.0 s -1

8. E LECTROMAGNETIC W AVES Form of electromagnetic radiation with electric and magnetic fields moving at the speed of light Carry energy from one place to another and are like waves on rope Do not require medium Energy traveling in straight line along path of wave Associated oscillating electrical field and oscillating magnetic field

9. E LECTROMAGNETIC W AVES

10. Light waves still characterized by wavelength, frequency, and velocity Velocity of all electromagnetic waves in vacuum same value (3.00 X 10 8 m/s), symbolized by c c =  What is the wavelength of an electromagnetic wave traveling in air whose frequency is 1.00 X 10 14 s -1 ? = c = 3.00 X 10 8 m/s = 3.00 X 10 -6 m  1.00 X 10 14 s -1

11. T HE E LECTROMAGNETIC S PECTRUM Frequency related to energy and amplitude of electromagnetic waves Frequency able to be converted to energy by multiplying by Planck’s constant ( h = 6.6 X 10 - 34 J  s) E = h  Wide range of frequencies, wavelengths, and energies in spectrum Electromagnetic spectrum – range of all possibilities of electromagnetic radiation

12. T HE E LECTROMAGNETIC S PECTRUM