enormous magnItude b≈9×100a6, while the gravitational force btwn masses ma and mb b=667×10-1020 For instance, two protons (Q=e=1.6x 10-C, mp=1.67 x 10-kg )at a distance of one meter Coulomb force: Fn10-28N gravitational force: FN 10-DN The Coulomb force is roughly 106 times greater than the gravitational force But, we have experienced much more influence of gray ity than Coulomb force Why? The Universe is presumedly neutral-cosmology
2.2 The electric field intensity e Definition: the electric field intensity due to the point charge cla is ab b2623 Explanation (1)it's the force exerted on a unit test charge; (2 )E has a unit volt/meter ( Ea is a vector field over the whole space (4)a exists as long as @a is present, regardless of Important (5)It' very simple to get the force acting on Q FEQE
2. 3 The principle of superposition If more than one charge are dis ibuted each generates a field e The resultant E is simply the vector sum of individual (r)=∑E2 Q r-r 2士丌enr-r where (r-ri)l is a unit vector pointing trom ri to. This is called the principle of superposition Explanation: (1) experimentally set up (2)theoretically, the Maxwell theory(equations )is a linear theory; so electromagnetism is easy to study, in comparison with other fundamental forces