2. 24 The Wave Nature of Light 24-5 Diffraction by a Single Slit or Disk Augustin Fresnel (1788-1827) Presented the wave theory with support from diffraction evidence. Simeon Poisson (1781-1840) pointed out a counter-intuitive inference that there should also be a bright spot in the center of the shadow…there was. See diffraction patterns on page 733.

3. 24-5 Diffraction by a Single Slit or Disk sin  D first minimum pg 734 Dsin  =m m=1,2,3…. minima pg 734 See Example 24-4 page 735

4. 24-6 Diffraction Grating A large number of parallel slits (or concentric) in a clear medium are called diffraction grating or transmission grating. A large number of parallel slits (or concentric) in a reflective medium are called reflection grating. dsin  =m m=1,2,3 principal maxima. Diffraction grating can produce a spectral separation also, like dispersion, but red is spread more and purple less. See Examples 24-6 and 24-7 page 737

5. 24-7 The Spectrometer and Spectoscopy dsin  =m m=1,2,3 so… = d/m (sin  White light produces a continuous spectrum, but when a gas or element is heated or electrified, it produces only the lines of light caused by the electron energy levels present… this is called a line spectrum. Absorption spectroscopy involves passing light through an element to observe missing lines… Emission spectroscopy involves burning or exciting an elements electrons to emit lines of light.

6. HOMEWORK Page 752 pr#18-21,26-28,31. BOP