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Edexcel Physics Unit 2 "Physics at work" June 2013 watch

  • View Poll Results: The last question - Does resistance increase or decrease?
    It increases ( using V=IR or some other method)
    70.73%
    It decreases using the 'lattice vibrations' theory
    29.27%

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    (Original post by Branny101)
    Could anyone explain, please?

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    Do you not understand how I explained it?
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    Anyone with Examiner's report for Jan 13 please? Urgent
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    (Original post by Tomupcraft)
    Do you mean out of phase or 180 degrees out of phase? out of phase can be anything that is not in phase with a point, wheres a point in anti phase must be 180 degrees out of phase.
    I meant 180 out of phase
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    (Original post by Tomupcraft)
    Do you not understand how I explained it?
    Sorry I just saw your reply, but doesn't frequency remain constant ?

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    (Original post by Branny101)
    Sorry I just saw your reply, but doesn't frequency remain constant ?

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    Yes, If blue light goes from air into water its frequency will remain constant but its speed will decrease and so will its wavelength as when you draw diagrams the waves get closer together.

    I wouldn't worry why shorter wavelengths refract more, just know that shorter wavelengths refract greater than larger wavelengths and therefore blue refracts more than red. So when you draw a diagram with a red and blue ray, the blue ray must refract closer to the normal.
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    (Original post by Tomupcraft)
    One time period is between adjacent compressions. If the wave had traveled T the positions would basically look the same, the particles would have just moved up the line. However as 3/4T has passed then the compressions must be 3/4 along the line between two compressions.

    If that does not make sense I will try to explain further.
    Hi, is there any chance you could explain further, the bits that I don't understand is, if one wavelength (distance from 2 adjacent compressions ) is the time period as the time period = the amount of time taken for one complete oscillation, then how do we know where the particles would be at t +3/4T, I find it really confusing? Thanks
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    (Original post by alygirl)
    I meant 180 out of phase
    If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

    Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

    However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
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    (Original post by LegendX)
    Hi, is there any chance you could explain further, the bits that I don't understand is, if one wavelength (distance from 2 adjacent compressions ) is the time period as the time period = the amount of time taken for one complete oscillation, then how do we know where the particles would be at t +3/4T, I find it really confusing? Thanks
    The wave travels at a constant speed. So if we take the first compression, in one time period that compression will be in the same position as the second compression. As it travels at a constant speed if half a time period had passed then the first compression must now be half way between its original position and the original position of the second position.

    If a tenth of a time period had passed then it would have been a tenth of the way along. Therefore if 3/4T has passed it must be three quarters between the original compression's.
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    (Original post by Tomupcraft)
    If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

    Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

    However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
    Thank youuuus , how is internal resistance measured?

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    Anyone please tell me how to do this?
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    (Original post by AT95)
    Anyone please tell me how to do this?
    I did that a couple pages back


    (Original post by CharlieTT)
    This is a combination of resistance in parallel and potential dividers equation.

    1/R1=1/R.1 + 1/R.2
    =1/6000Ohms +1/6000Ohms
    =1/3000Ohms
    R1=3 kiloOhms

    Vout=Vin x R2/(R1+R2)
    =12V x 6000Ohms/9000Ohms
    =2/3 x 12V
    =8V
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    (Original post by Tomupcraft)
    If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

    Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

    However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
    That makes sense. Sorry to bother you again, but please if you get a chance can you help me on Jan 2009 qu 13 b?
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    (Original post by Branny101)
    Thank young, how is internal resistance measured?

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    If we take a solar cell as an example.
    Have the solar cell in series with an ammeter and a variable resistor. Have a voltmeter in parallel with the solar cell.
    Vary the resistance and record current and voltage.

    as V = E - Ir rearrange to form V = -rI + E it is in the form y=mx+c
    V on y axis
    I on x axis
    therefore E will be y intercept
    so internal resistance, r will be the gradient.
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    (Original post by alygirl)
    That makes sense. Sorry to bother you again, but please if you get a chance can you help me on Jan 2009 qu 13 b?
    Current is split, if 30mA goes in then the current in both wires must = 30mA.
    20mA in one wire so 10mA in the other wire so I1 = 10mA
    15mA leave the first wire so 5mA must be remaining therefor I2 is 5mA
    as current is conserved and 30mA went in, 30mA must also leave therefore I3 must be 30mA.
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    (Original post by Tomupcraft)
    If we take a solar cell as an example.
    Have the solar cell in series with an ammeter and a variable resistor. Have a voltmeter in parallel with the solar cell.
    Vary the resistance and record current and voltage.

    as V = E - Ir rearrange to form V = -rI + E it is in the form y=mx+c
    V on y axis
    I on x axis
    therefore E will be y intercept
    so internal resistance, r will be the gradient.
    Thank you XD, what other experiments other than resistivity do we need to be able to understand and apply?

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    (Original post by Branny101)
    Thank you XD, what other experiments other than resistivity do we need to be able to understand and apply?

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    Standing waves
    Polarimetry
    Finding resistivity of a metal

    They are the main ones, I cannot remember any others off the top of my head.
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    (Original post by Tomupcraft)
    Standing waves
    Polarimetry
    Finding resistivity of a metal

    They are the main ones, I cannot remember any others off the top of my head.
    The standing waves is just a tube with lycopodium powder right?

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    (Original post by Branny101)
    The standing waves is just a tube with lycopodium powder right?

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    You mean Kundts tube? theres also the one with string attached to a mass hanging over a pulley.
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    (Original post by Tomupcraft)
    You mean Kundts tube? theres also the one with string attached to a mass hanging over a pulley.
    O__o... Let's stick with the glass tube ahaa

    Thanks BTW, for your help.

    EDIT: I just realised the experiment you meant

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    Can someone please tell me the equation to calculate path difference from phase difference? And the equations derived from the doppler effect, asap would be awesome
 
 
 
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