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Math Help - Ohms law

  1. #1
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    Post Ohms law

    A certain lightbulb filament when hot has a resistance of 205 Ω. The potential difference across the filament at a certain instant is standard household voltage, 120 V. (a) What current is flowing through the bulb at that time? (b) If the filament of the bulb is a tungsten wire having a radius of 475 μm, what is the magnitude of the current density in the filament?



    please help! i got (a)0.585365854A (b)123.2349166A/m^2 and both of the answers are wrong and i dont know how. a million thanks!!
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  2. #2
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    Using V = IR

    Your answer for a) looks correct to me. Sure you've read the question correctly?!

    What's the equation for current density?
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  3. #3
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    Quote Originally Posted by soojin89 View Post
    A certain lightbulb filament when hot has a resistance of 205 Ω. The potential difference across the filament at a certain instant is standard household voltage, 120 V. (a) What current is flowing through the bulb at that time? (b) If the filament of the bulb is a tungsten wire having a radius of 475 μm, what is the magnitude of the current density in the filament?



    please help! i got (a)0.585365854A (b)123.2349166A/m^2 and both of the answers are wrong and i dont know how. a million thanks!!
    For a) I suspect that either an exact answer or a more sensible rounding of the exact answer is required (since the answer you give has way more significant figures than the given data it is clearly ridiculous).
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