Hydroacoustics is the study of sound in water - Leaving Cert Physics - Question b - 2021

To demonstrate the Doppler effect in a laboratory setting, use a sound source (like a speaker) that produces a consistent frequency. Move the speaker towards a stationary microphone, and record the frequency detected by the microphone as the speaker approaches and then moves away from it. This change in frequency can be observed and measured, highlighting the effect.

Given:

• Frequency emitted by the source, $f_s = 800$ kHz
• Frequency detected, $f_d = 806$ kHz
• Speed of sound in water, $v = 1480$ m/s

Using the Doppler effect formula: $f_d = f_s \left( \frac{v}{v - u} \right)$ Where $u$ is the speed of the source.

Rearranging gives: $u = v \left( 1 - \frac{f_s}{f_d} \right)$

Substituting the values: $u = 1480 \left( 1 - \frac{800}{806} \right)$ $u = 1480 \left( 1 - 0.9917 \right)$ $u \approx 1480 \times 0.0083 \approx 12.31 \, m/s$ Thus, the speed of the source is approximately 12.31 m/s.

The refraction of sound waves can be illustrated by drawing a diagram that depicts the transition of a sound wave from water into air. The wave should make contact with the interface between the water and air, bending away from the normal as it travels into the air, demonstrating how the speed change affects the direction of the wave.