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

Click For Summary
SUMMARY

The discussion centers on the Doppler effect as it relates to sound waves emitted by a moving fire engine and ambulance. The original poster confused the concepts of wavelength and frequency, initially stating that the wavelength decreases when a fire engine moves away from an observer. The mark scheme clarified that the distance traveled by each wavefront increases, leading to a decrease in frequency. The poster later correctly identified that as the ambulance approaches, the distance between wavefronts decreases, resulting in an increase in frequency, aligning with the mark scheme's explanation of shorter wavelengths and higher frequency.

PREREQUISITES
  • Doppler effect in sound waves
  • Wavefront theory
  • Frequency and wavelength relationship
  • Basic principles of sound propagation
NEXT STEPS
  • Study the Doppler effect in detail, focusing on sound waves
  • Learn about wavefronts and their behavior in motion
  • Explore the mathematical relationship between frequency and wavelength
  • Investigate real-world applications of the Doppler effect in various fields
USEFUL FOR

Students preparing for physics exams, educators teaching sound wave concepts, and anyone interested in understanding the principles of wave behavior in motion.

Luke1121
Messages
14
Reaction score
0
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.
 
Physics news on Phys.org
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.
 

Similar threads

Replies
20
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
8
Views
2K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K