24 The Wave Nature of Light24-5 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.

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

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

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.

HOMEWORK

• Page 752 pr#18-21,26-28,31. BOP