Why is B(x,t)•l - B(x+dx,t)•l in Maxwell's Eqn 34.16?

[sparkle123]

Why is eqn 34.16
B(x,t)•l - B(x+dx,t)•l instead of
B(x+dx,t)•l - B(x,t)•l ?
Thanks!

 

[dynamicsolo]

The line integration is being followed around the rectangle counter-clockwise, so the segment along which the magnetic field is B is parallel to the direction of integration, while the segment with ( B + dB ) is anti-parallel to the integration direction.

 

[I like Serena]

Hi again sparkle123!

It's a matter of convention: one of the many applications of the right hand rule.
Point your thumb in the direction of the positive y-axis, and your fingers give the direction that is by convention positive.
This is shown by the arrowheads in the loop.

So B(x,t) is taken as positive, while B(x+dx,t) is taken as negative.

Edit: overtaken by dynamicsolo. ;)

 

[sparkle123]

Thanks dynamicsolo and I like Serena! :)