26) The force felt py a charged particle in a magnetic field is given by Lorentz force:
F=q(vxB) where q is charge, v is velocity, and B is the field vector.
Positive particles have positive charge +q
Negative particles have negative charge -q
So the forces are in opposite directions (they spiral in opposite directions).
27) The coil of a galvanometer is put in a constant magnetic field. When a current, I, is passed through the coil it creates a magnetic moment M=NIA where N is the turns of wire, A is the area of the loop, and I is current. This moment feels a torque in the field is MxB where "x" is the cross product. So the coil is rotated in the field by an amount proportional to its current.
28) DC travels in one direction only. AC changes directions twice per period. This makes it possible to transform the voltage later on, since Faraday's law requires the magnetic field created by a current to be changing in time. This is the main reason we use AC
