Wavelength of red light

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Quality of Measurement Coursework

Wavelength of red light

The Aim

The target is to take measurements to calculate the wavelength of red laser light by using the diffraction grating formula. Therefore I will use a variety of diffraction gratings. To improve accuracy I will always do the experiment with and in absence of two lenses. With this step I hope to get closer to the real wavelength.

The Set-up

Equipment list:

  1. red laser
  2. two metre rulers
  3. wall or projector screen
  4. double slit
  5. slit holder
  6. variety of diffraction gratings
  7. diverging lens
  8. converging lens
  9. two lens holders
  10. graph paper
  11. cello tape, blue tack
  12. marker pens

The light from the laser passes through the diverging lens and splits up. Afterwards the converging lens concentrates the light. This process gives a more focused and smaller dot on the wall which leads to higher accuracy. The grating causes the concentrated light to break up again. Maxima occur on the screen where the light is in phase. The dot in the centre is called central maximum or 0th order spectrum. The next dots left and right from the central maximum are called 1st order spectrum; the next ones are called 2nd order spectrum and so on.

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The measurements

  1. Set up the equipment
  2. Cut the graph paper into 4 stripes and glue them together to get one long stripe
  3. Stick the long stripe with blue tack on the wall
  4. Stick the laser to a fixed position and turn it on
  5. Adjust the diverging and converging lens to obtain a focused and small dot
  6. Insert the diffraction grating into the slit holder
  7. Measure the distance between the grating and the wall
  8. Mark the maxima on the graph paper with a pen
  9. Measure the length of the distance between central maximum and 1st order spectrum ...

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The method used gives a good value for the wavelength of laser light. Greater attention to the use of measurement techniques to reduce uncertainty would improve the grade. Also the final value should be compared to the stated value using a percentage deference calculation. 3 Stars