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    Can someone please see if I am approaching this question in the right way ?

    Q: Consider the filament of a 230 V 100 W lamp made from 500 mm Tungsten at resistivity (7 x 10^-7). What is the radius of the filament wire ?

    My answer so far:

    Using P=IV, 100=230i so current is 0.43 A. Now find resistance by R= V/I so (230/0.43) = 535 Ohms. Then substitute into the equation R=pL/A.

    Is this the right way to do this question ? Is my resistance correct ?


    Looks it to me. Shove the resistance, resistivity and length into the equation and there you are.
    But remember, you need to find radius, not area, so it's area=Pi*r^2
    So r=root of (area/pi.)
    Or at least, that's what I'd do
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