The Field Concept (continued)
Electric and Magnetic Fields at a given point in space determine the force on a “test” electric charge if it were placed at that point in space.
Electric field E causes force F = qE (q = charge)
Magnetic field B causes force F = qvB on charge moving with speed v perpendicular to B
This “harmless” equation has the seeds of trouble for the Newtonian picture!
- Magnetic force depends on the speed of the particle.
- Force is meant to be an absolute quantity. The laws of physics are supposed to be the same for two different observers (people or instruments) even if they are moving at constant v with respect to one another --- Remember Galileo, Newton !
- But speed is not the same to the different observers! What is going on? Will this lead to a breakdown of the ideas of Galileo and Newton?