CHAPTER 10. COLOUR 10.2
f =
c
λ
=
3 × 108
520 × 10 −^9
= 577× 1012 Hz
The frequency of the green light is 577 × 1012 Hz
Example 2: Calculating the wavelength of light given the fre-
quency
QUESTION
A streetlight also emits light with a frequency of 490 × 1012 Hz.
- What colour is the light? (Use table 10.1 to determine
the colour)
- What is the wavelength of the light?
SOLUTION
Step 1 : What is being asked and what information arewe given?
We need to find the colour and wavelength of light which has a
frequency of 490× 1012 Hz and which is emittedby the streetlight.
Step 2 : Compare the wavelength of the light to those given in table 10.1
We can see from table10.1 that orange light has frequencies
between 503 - 482× 1012 Hz. The light from thestreetlight has
f = 490× 1012 Hz which fits into this range. Therefore the light
must be orange in colour.
Step 3 : Next we need to calculate the wavelength of the light
We know that
c = f× λ
We know c = 3× 108 m.s−^1 and we are given that f = 490×
1012 Hz. So we can substitute in these values and solve for the
