Confused by Mark Scheme: Exam Q on Fire Engine Sound Wave

AI Thread Summary
The discussion revolves around confusion regarding the mark scheme for exam questions related to sound waves from moving vehicles, specifically fire engines and ambulances. The original poster initially misunderstood the relationship between pitch, wavelength, and wavefront distance, but later clarified their understanding by explaining how wavefronts change as a vehicle approaches or recedes. They noted that while the mark scheme emphasizes the distance traveled by wavefronts, their explanation aligns with the concept of frequency increasing as the source approaches. The poster questions whether the mark scheme's phrasing reflects a double standard in expressing the same underlying principles of sound wave behavior. Ultimately, the discussion highlights the importance of accurately interpreting the relationship between sound frequency, wavelength, and the motion of sound sources.
Luke1121
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I've just finished some past exam papers and when marking them using the mark scheme something confused me a little
One question said when a fire engine moves away from an observer, the pitch of the siren decreased, why and I chose the wavelength of the sound wave decreases
The mark scheme said the answer was the distance traveled by each wave front increases
I learned from my mistake and moved on. Today I've done another paper and a question says explain how the movement of the ambulance causes the frequency of the sound the man hears to change. Remembering my mistakes I talked about as the ambulance moves closer the distance traveled by each wavefront, decreases so there are more waves per second so f increases and the opposite for moving away, but the mark scheme said "higher frequency, wavelengths shorter as ambulance moves closer" Am I actually correct in what I'm saying or has the mark scheme got a case of double standards. Thanks in advance.
 
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Those answers look like different ways of expressing the same thing.

Personally, I'd focus on the the motion of the sound source decreasing the distance between wave fronts in the direction of motion and decreasing it behind.
 
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