2.Methods

Equipment List
  • A small, visible-light diffraction grating; a 500 lines/mm (12,700 lines/inch) linear grating (1)
  • Transparent adhesive tape (1 roll)
  • White LED bulbs (Watts ?)  (2)
  • CR2032 coin cell battery (2)
  • Electrical tape (1roll)
  • A small piece of wood or polystyrene, about 2 cm thick,
  • Baseplate template (link) used for cutting the wood/polystyrene
  • Cuvette, at least 3 ml (1)
  • Micro pipette (1)
  • Beakers, 100 ml each (6)
  • Deionised water (1 bottle)
  • Lens paper (1 box)
  • Surgical gloves (3 pairs)
  • Cell phone with camera (1) (iPhone 6S was used for this experiment)
  • Permanent marker (1)
  • A computer that can run the CPS upload software (1)
  • Lab notebook (1)
  • Water from water cooler (120ml )
  • Different water samples (40 ml each for the 6 samples)
  • Box (A4 sized) with no holes
Diagrams of experimental setup  

Photo 1:

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Photo 2:

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Procedure

Preparation

1.    On the assembly surface, select and tape the diffraction grating using the transparent tape, as shown in Photo 2. Make sure that diffraction grating is stable and is perpendicular to the surface of wooden base.
2.    Connect a battery to the white LED bulb using the two metal prongs provided. Secure the set-up electrical tape. Test to see if the white LED bulb lights up.
3. Position the LED-battery apparatus 15cm away from the front of diffraction grating. (Refer to Photo 1). Secure the LED-battery that is mounted on a small wooden base on the wooden base with masking tape.

Testing of Samples

  1. Extract 3.0 ml of the first water sample into the cuvette. Place it in front of the LED bulb, making sure that the smooth and transparent side of the cuvette is in direct contact with the LED bulb..
  2. Put the box over the set-up. Cut a hole in the box such that the lens of the phone’s camera completely covers it to take a photo of the light.
  3. Adjust the sample so that you can take a picture of the spectrum through the diffraction grating.
  4. Repeat the experiment with the other water samples using the same set-up for the measurement of the first water sample.

Analyzing your samples
  1. Unzip the file and open up “CellPhoneSpec.exe”
  2. Convert your spectrum image to .jpg format
  3. Load the your .jpg file of your spectrum from the phone on the program by clicking on File>Load Sample  (cell phone spectrometer)

Photo 3:


  1. Click on the blue and red ends of the spectrum, a green line across the spectrum should appear and click on “Absorbance” under Plot Trace selection and “Abscissa Selection click on “Wavelength (nm)”. After doing so, click on “Make Plot, Compute T, Compute A.

Photo 4:


3. To further analyse the data, absorbance versus wavelength by using the programme to plot a graph.

Photo 5:





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