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The filament in an incandescent light bulb is made from tungsten. The light bulb is plugged into a 240 V outlet and draws a current of 1.16 A. If the radius of the tungsten wire is 0.0052 mm, how long must the wire be?

  • physics -

    You need the restivity of the wire, lets say it is P ohm.m

    the cross sectional area (in m^2) of the wire is

    A=pi x (5.2x10^-6 m)^2

    so the resistamce per metre is

    P/A (units ohm/m)

    if the bulb draws 1.16 A from 240 V then the resistance, R, is

    R=240/1.16

    so the length of wire is

    R/(P/A)=RA/P

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