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    Two pieces of wire A and B are made of the same material but have different diameters. They are connected in series with each other and a power supply.

    (i) Which terms from the equation will be the same for both wires?
    (ii) The diameter of A is twice that of B. Calculate the ratio vA:vB

    For (i), I know it isn't A because A is area, and they have different areas so they also have different areas. However, I don't know which term it is.
    Please can you help me?

    (ii) I have no clue how to do this. Again, any help would be greatly appreciated.

    Thanks!
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    resistors in series have the same current flowing through them... That's often useful to know
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    (Original post by Ravenous food)
    What? Can you help me please?
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    assume the wires are circular in cross section... what happens to the area of a circle if you double it's diameter?
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    (Original post by blobbybill)
    What? Can you help me please?
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    (Original post by Joinedup)
    assume the wires are circular in cross section... what happens to the area of a circle if you double it's diameter?
    The area of the circle would double. I still don't get either of the questions though.
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    (Original post by blobbybill)
    The area of the circle would double. I still don't get either of the questions though.
    I'm pretty sure the Area will be as of 4 times the initial one.
    eg. A square with sides of 2cm. Area would be 4cm^2. If you double the length of the sides to 4cm, then the area would be 16cm^2.
    Hope this helps!
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    (Original post by blobbybill)
    The area of the circle would double. I still don't get either of the questions though.
    +Mrwaffle is right...

    also for circles where A=πr2

    doubling the diameter also doubles the radius so the area goes up by a factor 4

    this is interesting because the resistance of a wire depends on it's cross sectional area...
    ρ=RA/l
    ρ is a property of the material the wires are made of - and we're told they're made of the same material so ρ is the same for both.

    ρ=RA/l
    can be rearranged
    R=ρl/A

    so the wire that's got 1/4 the cross sectional area has 4 times more resistance for the same length.
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    (Original post by Joinedup)
    +Mrwaffle is right...

    also for circles where A=πr2

    doubling the diameter also doubles the radius so the area goes up by a factor 4

    this is interesting because the resistance of a wire depends on it's cross sectional area...
    ρ=RA/l
    ρ is a property of the material the wires are made of - and we're told they're made of the same material so ρ is the same for both.

    ρ=RA/l
    can be rearranged
    R=ρl/A

    so the wire that's got 1/4 the cross sectional area has 4 times more resistance for the same length.
    How do I do the question"The diameter of A is twice that of B. Calculate the radio vA:vB"? I think it means the v in the equation, so the drift velocity, but I don't get how to work out the answer to the question.

    Thanks
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    (Original post by blobbybill)
    How do I do the question"The diameter of A is twice that of B. Calculate the radio vA:vB"? I think it means the v in the equation, so the drift velocity, but I don't get how to work out the answer to the question.

    Thanks
    OK so the current is the same in both pieces of wire because they're in series... I is the same for both.
    n is a property of the material the wires are made of - and they're both made of the same material so n is the same for both wires.
    q is the charge per charge carrier - in metal wires the charge carrier is the electron and an electron in wire A carries the same charge as an electron in wire B


    A (area) is different for the 2 wires

    The formula says I=nAvq, if one of the wires has A 4 times larger than the other... and the only other variable that's able to change is v... what has to happen to v to keep I the same?
 
 
 
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