TFE4120 Electromagnetism: crash course
Assistant: Hallvar Haugdal E-451. [email protected]. Exercises help: proposal time 13:00-15:00 place: E-451.
Paticipants: should have Bsc in electronic, electrical/ power engineering. Aim of the course: Give students a minimum of pre-requisities to follow a 2-year master program in electronics or electrical /power engineering.
Electro-magnetism: interaction between electricity and magnetism. Michael Faraday (1791-1867) • In 1831 Faraday observed that a moving magnet could induce a current in a circuit. • He also observed that a changing current could, through its magnetic effects, induce a current to flow in another circuit.
James Clerk Maxwell: (1839-1879) • he established the foundations of electricity and magnetism as electromagnetism. Electromagnetism: Maxwell equations
• A static distribution of charges produces an electric field • Charges in motion (an electrical current) produce a magnetic field • A changing magnetic field produces an electric field, and a changing electric field produces a magnetic field.
Electric and Magnetic fields can produce forces on charges
Electricity and magnetism had been unified into electromagnetism! Coulomb’s law: force between electrostatic charges
풒ퟏ풒ퟐ 풒ퟏ풒ퟐ Scalar: 푭 = 풌 ퟐ = ퟐ 풓ퟏퟐ ퟒ흅휺ퟎ풓ퟏퟐ
풒ퟏ풒ퟐ Vector: 푭 = ퟐ 풓ෞퟏퟐ ퟒ흅휺ퟎ풓ퟏퟐ
풓ෞퟏퟐ is just for direction, its absolut value is 1.
The electrostatic force had the same functional form as Newton’s law of gravity The magnitude of the electrostatic force between two point charges: 1) directly proportional to the product of the magnitudes of charges 2) inversely proportional to the square of the distance between them 3) The force is along the straight line joining them. Vector force:
풏 풒풒 푭 = i 풓ෝ 풕풐풕 4흅휺 풓2 풊 풊=1 0 풊 Integration and vector caculus
dL direction Vector: Effective part of A is the the component along L direction
Vector: Effective part of A the the component along S direction S direction is perpendicular to the tangent plane to that surface at S
Scalar: no directon Gradient:Greatest rate of increase
P Gradient: 3 dimension derivative of a scalar function showing the direction and magnitude of the maximum spatial variation ( greatest rate of increase) of the scalar function V at a point space.
휕풇 휕풇 휕풇 훻풇 = 풙ෝ+ 풚ෝ+ 풛ො 휕푥 휕푦 휕푧 Divergence: Flux out of a point
Electric flux density: definition 푫 = 휀푬, independent of the material.
휕퐸푥 휕퐸푦 휕퐸푧 훻 ∙ 퐸 = + + 훻 ∙ 퐸 is a scalar. 휕푥 휕푦 휕푧 Divergence: Mathematical calculation Divergence theorem Curl: how much does a field circulate around a point.
휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 훻 × 퐴 = ( 푧- 푦)푥ො + ( 푥- 푧)푦ො + ( 푦- 푥)푧Ƹ 휕푦 휕푧 휕푧 휕푥 휕푥 휕푦 Curl
The curl around x-axis, in yz plane
Similar to the curl around y and z-axis
휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 훻 × 퐴 = ( 푧- 푦)푥ො + ( 푥- 푧)푦ො + ( 푦- 푥)푧Ƹ 휕푦 휕푧 휕푧 휕푥 휕푥 휕푦 Stokes’ Theorem Different coordinates
Spherial coordinate Cylindrical coordinate Cartesia Coordinate Examples: Probelm 3 Solutions: Solution for b Example:
휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 훻 × 퐴 = ( 푧- 푦)푥ො + ( 푥- 푧)푦ො + ( 푦- 푥)푧Ƹ 휕푦 휕푧 휕푧 휕푥 휕푥 휕푦 Solution for i) and ii) Conservative vector: solution for iii)
휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 휕퐴 훻 × 퐴 = ( 푧- 푦)푥ො + ( 푥- 푧)푦ො + ( 푦- 푥)푧Ƹ 휕푦 휕푧 휕푧 휕푥 휕푥 휕푦