How do i get this equation,(adsbygoogle = window.adsbygoogle || []).push({});

$$\frac{db}{dl}=(\hat{B}.∇)\hat{b}$$

This equation is a vector whose direction is towards the centre of the circle which most closely approximates the magnetic field-line at a given point, and whose magnitude is the inverse of the radius of this circle.

However I have no idea how to obtain the above and the source basically state it as by definition. Where is this equation obtained from?

Source: https://ocw.mit.edu/courses/nuclear...a-physics-i-fall-2003/lecture-notes/chap2.pdf page 8

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# I Calculating the curvature drift in a plasma

Have something to add?

**Physics Forums | Science Articles, Homework Help, Discussion**