# Isaac physics problem about phase and path difference D3.19

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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

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

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#2

(Original post by

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

**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

^{o}?

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.

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(Original post by

The phase difference posted in the question is not clear. Is it meant to read 0

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.

**uberteknik**)The phase difference posted in the question is not clear. Is it meant to read 0

^{o}?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.

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**uberteknik**)

The phase difference posted in the question is not clear. Is it meant to read 0

^{o}?

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.

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#5

(Original post by

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

**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

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#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

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#8

(Original post by

why is the path difference 0.5m? How was that calculated?

**NafzArt**)why is the path difference 0.5m? How was that calculated?

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."

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