Magnetic dipole and a torque

[mondo]

In reading chapter 6.1.2 I stumbled upon a magnetic torque concept which I don't understand, here is the problematic fragment

In the formula for N author multiplies by $sin(\theta)$ but why? The torque is said to be caused by forces (caused by magnetic field) on opposite side of a rectangular current loop. So there is no angle between them! They both lie in the same plane and are parallel to each other. IOW, the angle between is 0.
From the figure 6.2 it look like author takes an angle between m (magnetic dipole) and B (magnetic filed) but why if the torque is said to be generated by forces on opposite side of a rectangle?

 

[BvU]

Hi,

Here you find a comprehensive picture, with the accompanying text you should be able to answer your question.

Personally I find it instructive to fall back on the equation for the Lorentz force.

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