MadSci Network: Physics Query:

### Re: How do I measure wavelength blocked of transparent colored plastic?

Date: Fri Feb 6 09:42:49 1998
Posted By: Malcolm Tobias, Graduate Student, Physics, Washington University
Area of science: Physics
ID: 885343999.Ph
Message:
```
Its pretty hard to accurately measure the wavelength of light.  The problem
is that the wavelengths are very very small.  The wavelength of visible
light is about 1 millionth of a meter.  In order to accurately measure the
wavelength of visible light you need a sensitive tool called a
spectrometer.

With the help of a prism, you could roughly measure the wavelength of light
being filtered out by the colored wrap.  To do this, you'll first need
to measure the spectrum of the original light source.  Start by passing
the light through a small vertical slit.  You can make this out of
cardboard by cutting a slit, say, 10 cm tall and 1/2 cm wide.  Then pass
the light from this slit through a prism.  Shine the resulting 'rainbow' on
a white piece of paper and carefully note the colors that are present (it
would be helpful to do this in a very dark room).  Then, do the same
experiment, but place the filter between the light and the slit.  Carefully
note the color(s) that are missing.  You can then use these rough numbers
to determine the wavelengths that have been filtered out:

violet: 400 nm (1 nm = 1 nanometer = 1 meter/1,000,000,000)
blue:	500 nm
green:	550 nm
yellow:	600 nm
red:	650 nm

```

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