SME
Grade 8 Science · Physical Science
Wave properties and the electromagnetic spectrum
Use this for “A radio wave has a wavelength of 3 m. What is its frequency?”
Diagram
λ = 3 m: radio waves.
c = λ × f
300,000,000 m/s = 3 m × 100,000,000 Hz
This is an example. Type your own values to start a new problem.
300,000,000
m/s
=
λ (m)
×
f (Hz)
The picture’s c is the speed of light, 300,000,000 m/s, so its c = λ × f is this equation.
Formulas
300,000,000
=
λ
×
f
(300,000,000
=
wavelength
×
frequency)
300,000,000 = 3 × 100,000,000
Assumptions
•
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays are all the same kind of wave, at different wavelengths.
•
In empty space they all travel at the speed of light, 300,000,000 m/s.
•
Wavelength × frequency = speed, so a shorter wavelength means a higher frequency and more energy in each wave.
•
This page runs from 1,000 m radio waves to 10 nm ultraviolet. X-rays and gamma rays are shorter still.
Step-by-step
WE KNOW
λ = 3 m (wavelength)
FIND
frequency (f)
Step 1 · Find frequency (f)
Use 300,000,000 = λ × f (300,000,000 = wavelength × frequency)
Divide the speed of light by the wavelength: shorter waves pass by more often.
300,000,000
=
3
f
f
=
300,000,000
3
f
=
100,000,000
Hz
Check
Put the numbers back in. Both sides should match.
300,000,000 = 3 × 100,000,000 ✓
Topic check
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