The pitch of a musical note depends on its frequency - Leaving Cert Physics - Question b - 2008

The Doppler effect refers to the apparent change in frequency of a wave (including sound) when there is relative motion between the source of the wave and the observer. As the source moves towards the observer, the frequency appears higher, while it appears lower as the source moves away.

To calculate the change in pitch, we can use the Doppler effect formula:

$f' = f \frac{v + v_0}{v - v_s}$

Where:

• $f'$ is the observed frequency
• $f$ is the source frequency (1520 Hz)
• $v$ is the speed of sound in air (approximately 340 m/s)
• $v_0$ is the speed of the observer (0 m/s, as the observer is stationary)
• $v_s$ is the speed of the source (55 m/s)

1. For the car approaching:

   $f_{in} = 1520 \frac{340}{340 - 55} = 1813.33 Hz$

2. For the car moving away:

   $f_{out} = 1520 \frac{340}{340 + 55} = 1308.35 Hz$

3. The change in frequency ($\Delta f$) is:

   $\Delta f = f_{in} - f_{out} = 1813.33 - 1308.35 = 504.98 Hz$

Thus, as the car moves away, the change in pitch observed is approximately 211.65 Hz.

The Doppler effect has practical applications in various fields. For example, it is used in astronomy to measure the speeds of stars and galaxies through redshift and blueshift phenomena. Additionally, it is utilized in radar technology for measuring the speed of moving objects such as vehicles.