16.4 CHAPTER 16. OPTICAL PHENOMENA; PROPERTIES OF MATTER
Colour Wavelength range (nm)
violet 390 - 455
blue 455 - 492
green 492 - 577
yellow 577 - 597
orange 597 - 622
red 622 - 780
Table 16.2: Colours andwavelengths of light in the visible spectrum.
We also know that the energy of a photon of light can be found from:
E = hf =
hc
λ
Therefore if we know the frequency or wavelength of light, we can calculate the pho-
ton’s energy and vice versa.
Activity: Frequency, wavelengthand energy relation
Refer to table 16.2: Copy the table into your workbook and add two additional
columns.
- In the first new column write down the lower and upper frequencies for
each colour of light. - In the second column write down the energy range (in Joules) for each
colour of light.
Questions - Which colour of visible light has the highestenergy photons?
- Which colour of visible light has the lowestenergy photons?
Discharge lamps (sometimes incorrectly calledneon lights) use the spectra of various
elements to produce light of many colours.
See simulation: VPqea at http://www.everythingscience.co.za)
Example 4: Colours of light
QUESTION
A photon of wavelength500 nm is emitted by atraffic light.