1. PARTICLE NATURE OF LIGHT

2. A Black Object Appears black because it absorbs all frequencies of light A black block of iron does this

3. WHEN IRON IS HEATED Might expect the energy it has absorbed would radiate back out, exhibiting all the frequencies it had absorbed THIS IS NOT WHAT HAPPENS! Specific colors come out depending on the temperature of the metal Red Yellow White Blue-White HOTTER

4. Max Planck – Germany, 1900 “Matter can only gain or lose energy in small, specific amounts called QUANTA E quantum = h h = Planck’s Constant = 6.626 x 10 -34 J.s

5. EXAMPLE PROBLEMS 1. A metal is heated until it is red hot with a shade of red corresponding to a frequency of 4.42 x 10 14 Hz. What is the wavelength of this radiation? What is its energy in Joules?

6. EXAMPLE PROBLEMS 2. Tiny water drops in the air disperse the white light of the sun into a rainbow. What is the energy of the violet light that has a frequency of 7.23 x 10 14 Hz?

7. The Photoelectric Effect When light of a particular frequency shines on the surface of a particular metal, electrons are emitted. “photoelectrons”

8. The Photoelectric Effect Light of lower frequency produces no photoelectrons regardless of intensity or brightness. However, dim light of sufficient frequency produces“photoelectrons” Wave Theory fails to explain this!

9. Albert Einstein 1905 Expanded on Planck’s theory that EMR has a Dual Nature – Wave and Particle E photon = h  PHOTON – light particle or energy particle 

10. Planck & Einstein’s results reveal an important PARTICLE MODEL FOR LIGHT Example: It is found that light with a wavelength of 486 nm is necessary to produce photoelectrons from a photoelectric cell. What is the energy of this photon?

11. Planck & Einstein’s results reveal an important PARTICLE MODEL FOR LIGHT Example: It is found that light with a wavelength of 486 nm is necessary to produce photoelectrons from a photoelectric cell. What is the energy of this photon? ans 4.10 x 10 -19 J