Everything Science Grade 12

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.

1. In the first new column write down the lower and upper frequencies for
   each colour of light.


2. In the second column write down the energy range (in Joules) for each
   colour of light.
   Questions


3. Which colour of visible light has the highestenergy photons?


4. 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.