|Safe Current (A)||70||50||35||25||20||15||6||3|
|Current Density (A/mm2)||3.3||3.8||4.2||4.8||6.0||7.2||4.6||3.6|
b. R = rho L / (pi b2) = rho L/A.
b. 144 ohm
c. 0.833 A
d. The lightbulb filament is probably tungsten; the resistivity of metal increases with temperature. Since the temperature of a glowing filament is typically several thousand degrees, the resistance will be less when its turned off.
b. Denominator in power formula above also decreases with lowered voltage, so power drop is not as large as expected in (a).