# Question 4730f

May 30, 2015

Magnetic force (or any other force) may be measured using a torsion balance, which is a sensitive device to measure force.
Coulomb, himself used a torsion balance to discover the Coulomb's law and inverse square law of forces between magnetic poles.

Now, the magnetic force a magnetic field $B$ exerts on a charge $q$ moving with velocity $v$ making an angle $\theta$ with the field is given by the Lorentz force formula,

$F = q v B S \in \theta$

This gives an expression to calculate the magnetic force on a charged particle in a magnetic field.

Moreover, from the Coulomb's law of magnetic interations, the force of attraction (or repulsion) between two magnetic poles of pole strengths q""_m1 and $q \text{_m2}$ respectively separated by a distance $r$ is given by, (in vacuum)

$F = \frac{\mu {\text{_0*q""_m1q}}_{m} 2}{4 \pi {r}^{2}}$

where mu""_0# is the permeability of free space. The force acts along the line joining the magnetic poles.