The filament is cylindrical in shape, so we can use the formula for the area of a circle, which is $\pi r^2$. The radius is half the diameter, so $r = 0.5 \times 1.00 \, \text{mm} = 0.5 \times 10^{-3} \, \text{m}$. Therefore, the cross-sectional area $A$ is $\pi
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