《Fundamentals of Physics精品教学-华南理工》22 Electric Fields.pptVIP

Fundamentals of Physics 22 Electric Fields 22-1 What is Physics? How does q1 know the presence of q2 , and how can q1 exert a force on q2 ? q1 sets up an electric field in the space surrounding it. 22-2 The Electric Field Temperature field, Pressure field (Scalar fields) Velocity field (vector field) Fundamentals of Physics 22 Electric Fields Test charge — a probe, or detector The definition of electric field Test charge is only a tool R=U/I Two tasks Vector, SI unit: N/C 22-3 Electric Field Lines A nice way to visualize patterns in electric field The relation between field lines and electric field: 1 The direction of straight field line or the direction of the tangent to a curved field line gives the direction of electric field at that point. 2 The number of field lines per unit area is proportional to the magnitude of electric field. Fundamentals of Physics 22 Electric Fields Extend away from positive charge and toward negative charge (infinity) Fundamentals of Physics 22 Electric Fields 22-3 Electric Field Lines Perpendicular to sheet Uniform electric field Fundamentals of Physics 22 Electric Fields 22-3 Electric Field Lines Fundamentals of Physics 22 Electric Fields 22-3 Electric Field Lines 22-4 The Electric Field Due to a Point Charge Magnitude of electric field vector Direction of electric field: directly away from positive charge, and toward negative charge Fundamentals of Physics 22 Electric Fields Principle of superposition Fundamentals of Physics 22 Electric Fields 22-4 The Electric Field Due to a Point Charge Fundamentals of Physics Sample Problem The figure shows three particles with charges q1=+2Q, q2=-2Q, and q3=-4Q, each a distance d from the origin. What net electric field is produced at the origin? Electric Dipole Dipole axis Electric dipole moment Fundamentals of Physics 22 Electric Fields 22-5 The Electric Field Due to an Electric Dipole Permanent and Induced Dipole Moment Fundamentals of Physics