[NOTES/EM-01005]--Defining the Electric and Magnetic Fields

If a small test charge q is placed at a point and if the force on the charge is $\bar{F}$ , then the electric field $\bar{E}$ is defined to be  $$\bar{E}=\bar{F} / q$$ where q is positive. unit of $\bar{E}$ = [$\bar{E}$]={Newton/Coulomb}
The test charge must be very small so that it doesn't modify the electric field too much. The magnetic force on a moving charge depends on the direction of velocity;
1.Force is zero when $\bar{v}$ is parallel to $\bar{B}$
2.Force is maximum when $\bar{v}$ is perpendicular to $\bar{B}$
$$ \bar{B}= F_{\perp}/q_0\bar{v}$$
Unit of $\bar{B} =[\bar{B}]=\frac{{N}}{{Coulomb /(m/ s)}}= {N/(amp/m)}={Weber/m^2}$
$ 1 \ {Tesla} = {Weber/{m^2}}= {\mathrm {10^4\ Gauss}} $