1 / 14

Chapter 19 diffraction and interference of light

Chapter 19 diffraction and interference of light. Physics Mrs. Martin. Diffraction. The bending of light waves around a boundary Young’s Double Slit Experiment Allowed for the measurement of the wavelength of light Confirmed the wave theory of light Created an interference pattern

ina
Download Presentation

Chapter 19 diffraction and interference of light

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 19diffraction and interference of light Physics Mrs. Martin

  2. Diffraction • The bending of light waves around a boundary • Young’s Double Slit Experiment • Allowed for the measurement of the wavelength of light • Confirmed the wave theory of light • Created an interference pattern • The interference lines are equally spaced

  3. Young’s double slit • Must use a monochromatic light source • One that emits only one wavelength of light • Example: Laser light • This allows for coherent waves to strike the surface • The waves’ crests reach the same point at the same time • Resulted in banding pattern • Called interference fringes

  4. Diffraction of white light • Diffraction of white light causes the appearance of colored spectra instead of light bands and dark bands • This is due to the interference of different wavelengths of light

  5. Measuring the wavelength of light • The central band of light is called the central band • Each bright band on either side of the first central band is called the first order line • Where the bright bands are located, constructive interference occurs • Where there are dark bands, destructive interference occurs

  6. Measuring the wavelength of light • Formula • λ = xd/L • λ = wavelength (m) • x = distance between ordered bands (m) • d = distance between slits (m) • L = distance between the slit device and the screen (m) • Example • A two slit experiment is performed to measure the wavelength of red light. The slits are 0.0190 mm apart. A screen is placed 0.600 m away and the separation between the central bright line and the first-order bright line is found to be 21.1 mm. What is the wavelength of the red light?

  7. Homework Problems • Violet light falls on two slits separated by 1.90 x 10-5 m. A first order line appears 13.2 mm from the central bright line on a screen 0.600 m from the slits. What is the wavelength of the violet light? • Yellow-orange light from a sodium lamp of wavelength 596 nm is aimed at two slits separated by 1.90 x 10-5 m. What is the distance from the central line to the first order yellow line if the screen is 0.600 m form the slits?

  8. Single slit diffraction • Produces one wide central band and dimmer, smaller bands on the side • Because of the bending around the slit, destructive and constructive interference occurs

  9. Single Slit diffraction • These problems are solved exactly the same way, except the distance between slits now becomes the width of the slit and x is equal to the distance from the central band to the first dark band. • λ = xw/L (where w is the width of the slit) • Example • Monochromatic green light of wavelength 546 nm falls on a single slit with a width 0.095mm. The slit is located 75 cm from the screen. How far from the center of the central band is the first dark band?

  10. Homework problems • Yellow light falls on a single slit 0.0295 mm wide. On a screen 60.0 cm away, there is a dark band 12.0 mm from the center of the bright central band. What is the wavelength of light? • Light from a He-Ne laser (λ = 632.8 nm) falls on a slit of unknown width. A pattern is formed on a screen 1.15 m away on which the first dark band is 7.5 mm from the center of the central bright band. How wide is the slit?

  11. Diffraction gratings • A device that transmits light in the same way a double slit does. • Transmission gratings are made by scratching fine lines on a piece of glass. • Can have as many as 10,000 lines per centimeter • Reflective gratings are made by making scratches on a reflective surface. As in a CD

  12. Diffraction gratings • The interference pattern is the same as if using a double slit but the bright bands are narrower and the dark bands are broader and therefore more easily distinguishable. • Some instruments measure the distance between the first band, while others measure the angle. • Formula • λ = xd/L = d sin Θ • d is the distance between lines on the grating

  13. Diffraction grating • Example: • A spectrometer uses a grating of 12000 lines/cm. Find the angles at which red light, 632 nm, and blue light, 4321 nm have first order fringes.

  14. Telescope • Can have interference patter because the hole of the lens acts as a slit and spreads the light coming from a star out.

More Related