# Homework Help: Maxwell's equations

1. Aug 14, 2011

### 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!

2. Aug 14, 2011

### 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.

3. Aug 14, 2011

### 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. ;)

4. Aug 16, 2011

### sparkle123

Thanks dynamicsolo and I like Serena!! :)

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