Hello, Could someone please either verify my proof or find the error in it - its driving me nuts! if Torque (T) = Fd but F = BIlsin theta and F changes as you move around the circle 1. therefore to find F on the semi-circle: [tex]\int[/tex] between 0 and pi of BIlsin theta d theta = 2BIl ? 2. arc length 'l' of the semi circle is l = r phi -> l = r.pi 3. therefore F = 2BIrpi 4. into T= Fd -> T = 2BIrpi . 2r 5. therefore T = 4 BI. pi r squared 6. hence T = 4 BIA where A is the area of the circle? please! say this is wrong, every time i look at it i wish it was becuase T = BIA for all planar shapes is just so much more simple :) is faraday sufficiently spinning in his grave yet ?