LoginRegister
Nintendo Wii / Wii U Forum
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 18
  1. #1
    pull the trigger. AndThen?'s Avatar
    Member #
    27069
    Join Date
    Jun 2007
    Location
    Adelaide, Australia.
    Posts
    822
    Friends
    12
    Wii Friend Code: $post[field5]
    0000-0000-0000-0000

    Homework Help Thread ;D

    Okay, so I think this thread died in the crash and I could really use it right now.

    Uhmm, here's my question:

    Two small loudspeakers, A and B, are driven by the same amplifier (X) and emit pure sinusoidal waves in phase, The speakers are 3.00m from each other and point P is 4.00m from a line joining the two speakers as shown in the diagram below. Assume the speed of sound is 350m/s.


    A ----2.00m---X--1.00m--B
    ....................|
    ....................|
    .................4.00 m
    ....................|
    ....................|
    ....................P

    Determine the frequencies that
    i) constructive interference occurs at point P, and
    ii) destructive interference occurs at point P.

    This question's due in one and a half hours, so I doubt I'll get a reply, but this is revision stuff and it annoys me that I can't remember how to do it. So yeah, help would be great thankssss...


    Btw, this thread is for anyone who needs homework help, not just me.
    DISCLAIMER: Remember, this is "Homework Help Thread ;D" not "DO MY HOMMWORKZ FOR ME NAO THRED". Thanks for appreciating the difference.
    Last edited by AndThen?; 02-16-2009 at 05:39 AM.


  2. #2
    Super Moderator Eagles's Avatar
    WiiChat Moderator
    Member #
    22447
    Join Date
    Apr 2007
    Location
    Perth, Australia
    Posts
    1,877
    Friends
    28
    Wii Friend Code: $post[field5]
    5207-2685-9420-8549
    What actually is the question?

    This just seems like a description of the scenario to me:

    Quote Originally Posted by Dave
    Two small loudspeakers, A and B, are driven by the same amplifier (X) and emit pure sinusoidal waves in phase, The speakers are 3.00m from each other and point P is 4.00m from a line joining the two speakers as shown in the diagram below. Assume the speed of sound is 350m/s.
    It could be that I haven't done sound for a little while and I'm just not seeing it.

    Edit: Looks like you just added the question in, I'll have a look.
    Last edited by Eagles; 02-16-2009 at 05:11 AM.

  3. #3
    Super Ninjarator Foxy's Avatar
    WiiChat Moderator
    Member #
    20731
    Join Date
    Apr 2007
    Posts
    6,700
    Friends
    22
    Wii Friend Code: $post[field5]
    3881-9484-9041-5848
    i phuckin hate u ths thred was my idea and i wanted the credit! ffs i baggsed in the thnking thread



    For maths whip out Lew or the King

  4. #4
    pull the trigger. AndThen?'s Avatar
    Member #
    27069
    Join Date
    Jun 2007
    Location
    Adelaide, Australia.
    Posts
    822
    Friends
    12
    Wii Friend Code: $post[field5]
    0000-0000-0000-0000
    Physics, Foxy. ;D

    And yeah Pete, just edited it in there... forgot at first.. haha thought no one would notice. xD

  5. #5
    Super Ninjarator Foxy's Avatar
    WiiChat Moderator
    Member #
    20731
    Join Date
    Apr 2007
    Posts
    6,700
    Friends
    22
    Wii Friend Code: $post[field5]
    3881-9484-9041-5848
    Quote Originally Posted by AndThen? View Post
    Physics, Foxy. ;D

    And yeah Pete, just edited it in there... forgot at first.. haha thought no one would notice. xD
    I saw your diagram and that's all I saw, I jumped to con- ah forget it

  6. #6
    pull the trigger. AndThen?'s Avatar
    Member #
    27069
    Join Date
    Jun 2007
    Location
    Adelaide, Australia.
    Posts
    822
    Friends
    12
    Wii Friend Code: $post[field5]
    0000-0000-0000-0000
    C'monnn Pete, I'm waiting on you...

    EDIT: I SEE YOU THAR NAPALM

  7. #7
    Senior Member Napalmbrain's Avatar
    Member #
    43
    Join Date
    May 2006
    Location
    Cardiff, Wales
    Posts
    4,286
    Friends
    15
    Wii Friend Code: $post[field5]
    Quote Originally Posted by AndThen? View Post
    C'monnn Pete, I'm waiting on you...

    EDIT: I SEE YOU THAR NAPALM
    I can't remember how to do it and I can't be bothered to look.



    I never add friend codes.

    Quote Originally Posted by AndThen?
    @ROB64 - The longer you spend on this forum, the more you realise that Napalmbrain knows a lot about everything.


  8. #8
    Super Moderator Eagles's Avatar
    WiiChat Moderator
    Member #
    22447
    Join Date
    Apr 2007
    Location
    Perth, Australia
    Posts
    1,877
    Friends
    28
    Wii Friend Code: $post[field5]
    5207-2685-9420-8549
    First I'd work out the path difference.

    Distance from A to P = Sqrt (2^2 + 4^2) ≈ 4.5 m

    Distance from B to P = Sqrt (1 + 16) ≈ 4.1 m

    These seem like untidy numbers, so could be doing it totally wrong.

    Thus path difference ≈ 0.4 m.

    You'll have constructive interference when the path difference is a multiple of the wavelength or zero.

    So you'll have constructive interference when λ = 0.4 m, 0.2 m, 0.1333 m, 0.1 m etc. [Using your speed of sound.]

    Thus constructive frequencies are: f = v / λ : 875 Hz, 1750 Hz, 2625 Hz, 3500Hz etc.

    I'm not sure if this is right, I haven't done sound for a while. What do you think?

    If this is right, you'll have the destructive interference when the path difference is a multiple of λ/2.
    Last edited by Eagles; 02-16-2009 at 05:42 AM.

  9. #9
    pull the trigger. AndThen?'s Avatar
    Member #
    27069
    Join Date
    Jun 2007
    Location
    Adelaide, Australia.
    Posts
    822
    Friends
    12
    Wii Friend Code: $post[field5]
    0000-0000-0000-0000
    Aw, mannn... Anyway, there's plenty of physics to go around! I really don't remember how to do sound-in-a-tube questions, and they always appear in the exams.

    A tube that is open at both ends is placed in a deep tank of water. A tuning fork of frequency 256 Hz is sounded continuously above the tube. The tube is slowly raised out of the water and, at a position of the tube, a maximum loudness of sound is heard.

    The tube is gradually raised from a position of maximum loudness until the next position of maximum loudness is heard. The length of the tube above the water surface is increased by 65.0 cm. Calculate the speed of sound in the tube.


    Care to help? I'd like to know how to do it, not just the answer pl0x.

    EDIT:
    Petey, that looks alright to me, but it says the lowest frequency that the destructive/constructive interference occurs... I know I didn't say that earlier but neither did the quiz.

  10. #10
    Super Moderator Eagles's Avatar
    WiiChat Moderator
    Member #
    22447
    Join Date
    Apr 2007
    Location
    Perth, Australia
    Posts
    1,877
    Friends
    28
    Wii Friend Code: $post[field5]
    5207-2685-9420-8549
    Spotted a mistake in my answer post, all fixed up now. The correct equation is: f = v / λ.
    Quote Originally Posted by Dave
    Petey, that looks alright to me, but it says the lowest frequency that the destructive/constructive interference occurs... I know I didn't say that earlier but neither did the quiz.
    Well that's ok, the lowest frequency refers to the longest wavelength. So just use the path difference as the wavelength. So you'll get 875 Hz as the lowest frequency. Are you getting what I'm doing?

    Want to try ii] yourself?

    Disclaimer: I may be giving you the wrong answers, it happens occasionally.
    Last edited by Eagles; 02-16-2009 at 05:47 AM.

Ads

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Search tags for this page

"two small loudspeakers, a and b"

,

two loudspeakers are driven by same amplifier what is the lowest frequency for which constructive interference occurs

Click on a term to search for related topics.