Final answer:
When an emergency vehicle is approaching with its siren on, you should slow down, determine the location of the vehicle, and move to the edge of the road. Understanding the Doppler effect can help determine when the vehicle is closest to you when its pitch will match its actual siren frequency, and to make informed decisions about moving over.
Step-by-step explanation:
When you hear the siren of an emergency vehicle approaching from behind while you're driving, the correct action to take is to slow down, determine where the emergency vehicle is, and then move toward the edge of the road to let it pass safely. This response is best encapsulated by option B. Speeding up or ignoring the siren is dangerous and against the law while honking your horn is unnecessary and could confuse other drivers.
The Doppler shift is an important phenomenon to understand when relating to the sound of an approaching emergency vehicle. As the vehicle gets closer, the pitch of the siren increases due to the Doppler effect and then decreases as it moves away. You can use this change in pitch to help identify whether you need to pull over. An emergency vehicle's siren will sound higher in pitch as it approaches you, and the pitch will drop as it passes and gets further away.
GRASP CHECK: The frequency you observe will most closely match the actual frequency of the siren when the ambulance is directly in front of you, that is, option C. Before it reaches you, the frequency will seem higher, and after it passes, the frequency will seem lower.
Experience with the Doppler effect can provide you with an understanding of the urgency of the situation. For instance, if you're driving next to a train and you notice a drop in the pitch of its horn, it could indicate that you are moving away from the train or that the train is moving away from you.
Understanding the Doppler effect can also extend to calculating differences in the perceived frequencies of sirens and the speed of an ambulance or other emergency vehicles. For example, knowing the Doppler effect helps you comprehend why the pitch of the siren changes as it passes by you and how the perceived frequency can give you clues about the vehicle's speed relative to you.