Final answer:
When you hear an emergency vehicle siren while driving, you should identify its position using the Doppler effect, then pull over to let the vehicle pass. The frequency of the siren highest indicates the vehicle is approaching, and lowest when it moves away, with the actual frequency when directly in front of you.
Step-by-step explanation:
If you hear an emergency vehicle siren while driving, the action you should take is based on understanding the principles of the Doppler effect. As an emergency vehicle with a siren approaches, the pitch of the siren appears higher because the sound waves are compressed, making the frequency of the sound higher. After the vehicle passes, the pitch of the siren becomes lower because the sound waves are stretched out, reducing the frequency. Not only will you be able to notice an increase in pitch as the emergency vehicle comes closer, but you'll also observe a decreased pitch as it moves away. This provides a cue for when to pull over and let the vehicle pass. Additionally, when the emergency vehicle's siren matches the actual frequency of its siren without any pitch change, it would most likely be directly in front of you, indicating that it's time to stay stationary and clear a path.
If you are standing still and an ambulance circles around you on a circular road, you will experience continuous changes in the pitch of the siren due to the Doppler effect. The pitch will be highest when the ambulance approaches you and lowest when it moves away. If the ambulance maintains a consistent speed, the frequency shift will be smooth and continuous around the circle, which is a manifestation of the Doppler shift.