Wave Speed Physics Example 4

Follow the full solution, then compare it with the other examples linked below.

Example 4

medium
The speed of sound in air at 20°C20°\text{C} is 343 m/s343 \text{ m/s} and in water is 1480 m/s1480 \text{ m/s}. A 500 Hz500 \text{ Hz} tone travels from air into water. Does the frequency or wavelength change? Calculate the wavelength in each medium.

Solution

  1. 1
    Frequency does NOT change when a wave crosses a boundary — it stays at 500 Hz500 \text{ Hz}.
  2. 2
    In air: λair=vf=343500=0.686 m\lambda_{\text{air}} = \frac{v}{f} = \frac{343}{500} = 0.686 \text{ m}.
  3. 3
    In water: λwater=1480500=2.96 m\lambda_{\text{water}} = \frac{1480}{500} = 2.96 \text{ m}.
  4. 4
    The wavelength increases because wave speed is higher in water.

Answer

λair=0.686 m;λwater=2.96 m\lambda_{\text{air}} = 0.686 \text{ m}; \quad \lambda_{\text{water}} = 2.96 \text{ m}
When a wave enters a new medium, speed and wavelength change but frequency stays constant. This is because the source still vibrates at the same rate — each crest entering the new medium must exit at the same rate.

About Wave Speed

Wave speed is the distance a wave pattern travels each second through a medium.

Learn more about Wave Speed →

More Wave Speed Examples

Example 1 easy

A sound wave has a frequency of [formula] and a wavelength of [formula]. What is the speed of sound?

Example 2 medium

A seismic wave travels [formula] in [formula]. What is its speed? If the frequency is [formula], wha

Example 3 medium

An electromagnetic wave has a frequency of [formula]. What is its wavelength? Use [formula].

Example 5 medium

A sound wave has frequency 440 Hz and wavelength 0.773 m. Calculate the speed of sound.

← All Wave Speed Examples Wave Speed Concept