2nd step - The effect of magnetic fields on moving charged particles

Magnetic field curve the trajectory of charged particles. Positively charged particles are curved in one direction, negatively in opposite direction (move cursor onto and off the picture).

Usually it is not necessary to be told which way is field pointing - the picture already contains the answer. The little curly tracks are produced by electrons which are knocked out of the atoms by charged particles passing by.

Electrons spiral because they are much lighter than all other charged particles and lose energy quickly by another process called bremsstrahlung.