Isaac physics problem about phase and path difference D3.19

Watch
astudent...
Badges: 11
Rep:
?
#1
Report Thread starter 3 years ago
#1
Hi everyone,
I'm confused about this question from Isaac physics

Two speakers are set up 13.5m apart in an auditorium, pointing at each other. A pure sound of frequency 256Hz is being played through them. You may assume that the phase difference of the signals as they arrive at the speakers is 0∘. A person is standing on the line joining the speakers, 0.25m from the mid point. Calculate the phase difference as it would be detected by the person. And the speed of sound in air is given as 330m/s

I worked out the wavelength as 330/256=165/128

Phase difference = ( path difference / wavelength ) (2pi or 360)

= ( 0.5 / (165/128) ) (2pi or 360)
giving me a phase difference of 2.4 radians or 140 degrees to 2 sf

Isaac physics doesn't just say my answer is wrong but that it both of these are not valid numbers

Could someone explain where I have gone wrong please
thanks
0
reply
uberteknik
  • Study Helper
Badges: 21
Rep:
?
#2
Report 3 years ago
#2
(Original post by astudent...)
Hi everyone,
I'm confused about this question from Isaac physics

Two speakers are set up 13.5m apart in an auditorium, pointing at each other. A pure sound of frequency 256Hz is being played through them. You may assume that the phase difference of the signals as they arrive at the speakers is 0∘0∘. A person is standing on the line joining the speakers, 0.25m from the mid point. Calculate the phase difference as it would be detected by the person. And the speed of sound in air is given as 330m/s

I worked out the wavelength as 330/256=165/128

Phase difference = ( path difference / wavelength ) (2pi or 360)

= ( 0.5 / (165/128) ) (2pi or 360)
giving me a phase difference of 2.4 radians or 140 degrees to 2 sf

Isaac physics doesn't just say my answer is wrong but that it both of these are not valid numbers

Could someone explain where I have gone wrong please
thanks
The phase difference posted in the question is not clear. Is it meant to read 0o ?

Centre point is 13.5/2 = 6.75m from both speakers.

If the listener stands 0.25m off centre, then one speaker will be 6.5m from the listener, while the other is 7.0m from the listener.

i.e. an equivalent phase difference of 0.5m separation.

Your answer looks O.K.
2
reply
astudent...
Badges: 11
Rep:
?
#3
Report Thread starter 3 years ago
#3
(Original post by uberteknik)
The phase difference posted in the question is not clear. Is it meant to read 0o ?

Centre point is 13.5/2 = 6.75m from both speakers.

If the listener stands 0.25m off centre, then one speaker will be 6.5m from the listener, while the other is 7.0m from the listener.

i.e. an equivalent phase difference of 0.5m separation.

Your answer looks O.K.
Thanks, I re entered the answer this morning and it went in fine so maybe I entered it wrong yesterday or a glitch on the site but anyway, thanks for the help
1
reply
astudent...
Badges: 11
Rep:
?
#4
Report Thread starter 3 years ago
#4
(Original post by uberteknik)
The phase difference posted in the question is not clear. Is it meant to read 0o ?

Centre point is 13.5/2 = 6.75m from both speakers.

If the listener stands 0.25m off centre, then one speaker will be 6.5m from the listener, while the other is 7.0m from the listener.

i.e. an equivalent phase difference of 0.5m separation.

Your answer looks O.K.
I'm sorry, I've tried to give you rep for this but apparently I need to rate some other people first so I'll keep trying
0
reply
ali2002
Badges: 3
Rep:
?
#5
Report 1 year ago
#5
(Original post by astudent...)
Hi everyone,
I'm confused about this question from Isaac physics

Two speakers are set up 13.5m apart in an auditorium, pointing at each other. A pure sound of frequency 256Hz is being played through them. You may assume that the phase difference of the signals as they arrive at the speakers is 0∘. A person is standing on the line joining the speakers, 0.25m from the mid point. Calculate the phase difference as it would be detected by the person. And the speed of sound in air is given as 330m/s

I worked out the wavelength as 330/256=165/128

Phase difference = ( path difference / wavelength ) (2pi or 360)

= ( 0.5 / (165/128) ) (2pi or 360)
giving me a phase difference of 2.4 radians or 140 degrees to 2 sf

Isaac physics doesn't just say my answer is wrong but that it both of these are not valid numbers

Could someone explain where I have gone wrong please
thanks
how do you do part B
1
reply
LeMental
Badges: 2
Rep:
?
#6
Report 9 months ago
#6
using the answer from the previous questionwe know that 140 degrees = 0.5m phase difference, you want phase difference at 90 degrees for the detruscitve, so alegebra can help us0.5m = 140 d0.5/140 = 1d0.5/140 x 360 = 0.32 which is the answer in issac physics
0
reply
NafzArt
Badges: 1
Rep:
?
#7
Report 1 month ago
#7
why is the path difference 0.5m? How was that calculated?
0
reply
tomjread
Badges: 1
Rep:
?
#8
Report 1 month ago
#8
(Original post by NafzArt)
why is the path difference 0.5m? How was that calculated?
That's the distance between the person and one speaker, minus the distance between the person and the other speaker.

What someone else said in this thread -

"Centre point is 13.5/2 = 6.75m from both speakers.

If the listener stands 0.25m off centre, then one speaker will be 6.5m from the listener, while the other is 7.0m from the listener.

i.e. an equivalent phase difference of 0.5m separation."
0
reply
NafzArt
Badges: 1
Rep:
?
#9
Report 1 month ago
#9
oh, of course! Thank you so much for explaining that.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Have the latest Covid-19 announcements affected your decisions about university?

It's complicated, I'll tell you more in the thread... (35)
6.43%
I've decided not to go to university (26)
4.78%
I'm more likely to go to university now (32)
5.88%
I've decided to go to a university nearer to my home town (42)
7.72%
I’m considering different universities (31)
5.7%
I am choosing a more career-related course (38)
6.99%
I am choosing a course based on what I’m passionate about (69)
12.68%
It hasn't changed anything for me (271)
49.82%

Watched Threads

View All