What are the main differences between magnetic and electric fields?

Magnetic and electric fields share many similarities and symmetries (for example they both act on electric charge and obey an inverse square law of force), but there are some important differences. One difference is in the ways the fields can be created. An electric charge will always be accompanied by an electric field. There is no such thing as a "magnetic charge": instead magnetic fields are created when electric charges move. Another way magnetic fields can be created is through the "magnetic moment" associated with fundamental particles (this involves a quantum mechanical quantity called spin and is usually beyond the scope of A-level Physics). The absence of magnetic charge in Physics is the reason why a magnet must always have a North and a South pole, while an electric field can come from a single point in space (an electric monopole). Another important difference is in the force a charged particle experiences in each type of field. In an electric field, the particle will experience a force in the direction of the field, regardless of the motion of the particle. In a magnetic field, the particle will experience a force perpendicular to both the magnetic field direction and its direction of travel. This means that charged particles will never gain kinetic energy from a magnetic field, because the magnetic force will only change the direction of motion and not the total speed. The trajectory of a charged particle in an electric field will tend to be a straight line or a curve, while the general trajectory of a charged particle in a magnetic field will be a spiral. Any of the above points can be discussed more quantitatively or in more depth on the whiteboard upon request. Application of these concepts to example exam questions may be especially helpful.