How to study EM Always think: Positively Always ask: Why? Always do: The drills as more as you can Language: Progressively to transfer Chapter 1 Electric field of stationary charges
How to study E.M. • Always think: Positively! • Always ask: Why? • Always do: The drills as more as you can. • Language: Progressively to transfer Chapter 1 Electric field of stationary charges
1.1 Coulomb law 1.1.1. What is electric charge? This is a question never be answered EC is a quantity derived from electric phenomena 1.1.2. How to define the electric charge? 1 Coulomb. In MKsAunit system, 1C=1A1S Concept: The observatory phenomena is attraction, the measurement quantity is the force, therefore the electric charge is only a definition in the beginning, but lateron 1.1.3. Character of the electric charge Quantum unit of the charge: charge for electron e=1. 6021892X10-19C Conservation of the charge (how to understand the creation of the charge?), Difference with mass(deep discussion 1.1. 4 Torsion experiment and coulomb law Physics starts from torsion pendulum experiments and continues with torsion pendulum experiments The description of Coulomb law: The force between two point charges is proportional to the product of charges and inversely proportional to the square of the distance
1.1 Coulomb Law 1.1.1. What is electric charge? This is a question never be answered. EC is a quantity derived from electric phenomena. 1.1.2. How to define the electric charge? 1 Coulomb . In MKSA unit system, 1C=1A1S Concept: The observatory phenomena is attraction, the measurement quantity is the force, therefore the electric charge is only a definition in the beginning, but later on……. 1.1.3. Character of the electric charge Quantum unit of the charge: charge for electron, e=1.6021892X10-19C Conservation of the charge (how to understand the creation of the charge?); Difference with mass (deep discussion) 1.1.4. Torsion experiment and Coulomb law Physics starts from torsion pendulum experiments and continues with torsion pendulum experiments. The description of Coulomb law: The force between two point charges is proportional to the product of charges and inversely proportional to the square of the distance
Comparison of electric charge and mass Characters Electric ass Charge (gravitational) Property Positive/neg Only ative positive Interaction yes yes Quantization yes no Lozents variation Invariance covariance conservation yes E=mc2 Different definition no Gravitation inertial
Characters Electric Charge Mass (gravitational) Property Positive/neg ative Only positive Interaction yes yes Quantization yes no Lozents variation Invariance covariance conservation yes E=mc2 Different definition no Gravitation al/inertial Comparison of electric charge and mass
Coulombs experiment suspension head fiber
Coulomb’s experiment
The expression of Coulomb law F 1 2Q A兀So Where 8 is the permittivity at vacuum(. 854x10-12farad/m) Discussion 1) Whether the inverse square law is accurate or not To be determined by the experiment 2)Only valid for stationary point charges 3)Vector property for the interaction Comment: a) The limitation of the theory is depending upon the validity of 1) b) The complication of the complete theory of electric field is due to 2 and 3)
The expression of Coulomb law: r r Q Q o a b o F 2 4 1 = Where o is the permittivity at vacuum (8.854x10-12farad/m) Discussion: 1) Whether the inverse square law is accurate or not. To be determined by the experiment 2)Only valid for stationary point charges 3) Vector property for the interaction Comment: a) The limitation of the theory is depending upon the validity of 1) b) The complication of the complete theory of electric field is due to 2) and 3)