diffraction grating experiment

• equipment

  • laser
  • diffraction grating
  • white screen
  • metre ruler
• method

  • set up apparatus in partially darkened laboratory
  • adjust so distance between grating and screen is 1m
  • measure distances between same-order diffraction lines on either side of the central maximum and find the mean
• graphs and calculations

  • work out slit separation
  • reciprocal of number of slits per metre
  • find angle between first-order line and nth-order line
  • $\theta_n=$$\arctan\left(\frac{h_n}{D}\right)$
  • find wavelength and calculate mean
  • $\lambda=$$\frac{d\sin\theta}{n}$
• safety

  • laser in eyes is dangerous

  precaution

  • keep away from eye level
  • only turn on when using
• improvements

  • ensure screen and slit are aligned perfectly normal to the laser to avoid parallax error in measurement of fringe width
  • set square used with ruler