SME
Grade 11 Science · Physics
Waves and sound: wave properties, standing waves and the Doppler effect
Use this for “A 440 Hz note travels at 343 m/s. What are its wavelength and period?”
Diagram
Crest to crest is one wavelength, 0.78 m.
The crest rises 0.02 m above the middle.
440 waves pass each second.
Wave speed: 343 m/s
Period: 0.00227 s
This is an example. Type your own values to start a new problem.
v (m/s)
=
f (Hz)
×
λ (m)
T
Period
calculated
A
Amplitude
example
Formulas
v
=
f
×
λ
343 = 440 × 0.78
T
=
1
f
0.00227
=
1
440
Assumptions
•
The medium sets the wave speed, so a new frequency changes the wavelength, not the speed.
•
The amplitude is the loudness (or the height of the wave): it doesn’t change λ or v.
•
Sound in air at 20 °C travels at 343 m/s.
•
Light and radio waves travel at 3.00 × 10⁸ m/s in a vacuum.
Step-by-step
WE KNOW
v = 343 m/s, f = 440 Hz, A = 0.02 m
FIND
wavelength (λ), period (T)
Step 1 · Find wavelength (λ)
Use v = f × λ
The speed over the frequency.
λ
=
v
f
λ
=
343
440
λ
=
0.78
m
Step 2 · Find period (T)
Use T = 1/f
The period is the time for one wave: 1 over the frequency.
T
=
1
440
T
=
0.00227
s
Check
Put the numbers back in. Both sides should match.
343 ≈ 440 × 0.78 ✓
0.00227
≈
1
440
✓
Topic check
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