SME
Grade 8 Science · Problem type
Colors of visible light
Use this for “Which color of light has the longest wavelength?” and “How many waves of green light fit in one millimeter?”
Diagram
λ = 500 nm: visible light (green).
w = 2,000 (waves in one millimeter)
This is an example. Type your own values to start a new problem.
λ
Wavelength
example · nm
w
Waves in one millimeter
worked out (not typed)
Formulas
w
=
1,000,000
÷
λ
(waves
in
one
millimeter
=
1,000,000
÷
wavelength)
2,000 = 1,000,000 ÷ 500
Assumptions
•
Visible light runs from red at about 700 nm to violet at about 400 nm. A nanometer is a billionth of a meter.
•
Red has the longest wavelength and the least energy per wave; violet the shortest and the most.
•
Beyond red is infrared, felt as heat; beyond violet is ultraviolet, which sunburns.
Step-by-step
WE KNOW
λ = 500 nm (wavelength)
FIND
waves in one millimeter (w)
Step 1 · Find waves in one millimeter (w)
Use w = 1,000,000 ÷ λ (waves in one millimeter = 1,000,000 ÷ wavelength)
A millimeter is 1,000,000 nanometers: divide it by one wave’s length.
w
=
1,000,000
500
w
=
2,000
(green
light)
Check
Put the numbers back in. Both sides should match.
2,000 = 1,000,000 ÷ 500 ✓
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