RP: Young's Slit Experiment and Diffraction Gratings

• What is the overall aim of Young's Double-Slit Experiment?

  Investigate the relationship between D and w
• What is the independent variable in Young's Double-Slit Experiment?

  Distance between the slits and the screen, D
• What is the dependent variable in Young's Double-Slit Experiment?

  Fringe width, w
• What are the control variables in Young's Double-Slit Experiment?

  Wavelength of laser light, λ and slit separation, s
• What is the method for measuring fringe width in Young's Double-Slit Experiment?

  1. Set up apparatus with D = 0.5 m
  2. Darken room and turn on laser
  3. Measure from central fringe using vernier callipers
  4. Divide by number of fringe widths for w
  5. Increase D by 0.1 m and repeat
  6. Calculate mean fringe width for each D
• What is the fringe spacing equation in Young's Double-Slit Experiment?

  w = λD/s

  
• How does the fringe spacing equation relate to a straight line equation?

  It compares to y = mx with y = w
• What is the gradient in the fringe spacing equation?

  Gradient = λ/s
• What is the aim of the diffraction grating experiment?

  • Calculate the wavelength of laser light
  • Use a diffraction grating
• What is the independent variable in the diffraction grating experiment?

  Distance between maxima, h

  
• What is the dependent variable in the diffraction grating experiment?

  Angle between the normal and each order, θ

  
• What are the control variables in the diffraction grating experiment?

  Distance D, laser wavelength λ, slit separation d

  
• What is the method for measuring distance between maxima in the diffraction grating experiment?

  1. Place laser on retort stand
  2. Ensure beam passes through grating at normal incidence
  3. Set D = 1.0 m
  4. Darken room and turn on laser
  5. Identify zero-order maximum
  6. Measure distance h to first-order maxima
  7. Calculate mean of two values
  8. Measure h for increasing orders
  9. Repeat with different slit numbers

  
• What is the diffraction grating equation?

  nλ = d sin θ
• What does the variable 'n' represent in the diffraction grating equation?

  The order of the diffraction pattern
• What is the accepted wavelength for a standard school red laser?

  635 nm
• What are the systematic errors in the experiments?

  • Use set square to avoid parallax error
  • More lines per mm lowers percentage uncertainty
  • Measure distance between bright fringes accurately
• What are the random errors in the experiments?

  • Subjective fringe spacing based on intensity
  • Take multiple measurements of w and h
  • Use Vernier scale for accuracy
  • Measure across all visible fringes
• What safety considerations should be taken with lasers?

  Class 2 lasers, max output 1 mW
• Why should reflective surfaces be removed from the room during laser experiments?

  To prevent laser light reflection into eyes
• How can you calculate the mean wavelength of laser light?

  • Use recorded distances between maxima
  • Compare with accepted value of 635 nm
  • Assess percentage uncertainty