Mathematics is key to understanding physics. Many physics articles have the unforunate problem that they dive deep into mathematics without establishing a context. This make many such articles incomprehensible.
Another issue is that some mathematical constructs can be written in different ways. Each construct is valid provided that it is used consistently.
Also, the mathematics describing a physical phenomenon can
often the derived in several different ways. An equation can
sometimes be written in different forms. There are also
shorthand notations used to simplify equations. It is also
common to get rid of constants by setting their value to
If a scalar field, which is a function of position, is
This is a vector field that points in the direction of greatest change in the scalar field.
The divergence of a vector field
The Laplacian is the divergence of a gradient. It is a scalar second deriviative of a scalar field that represents the curvature of the field.
There is also a vector Laplacian.
The curl of a vector field
As a curl is a cross product it is perpendicular to both vectors. The dot product of thwo perpendicular vectors is always zero. Hence, the divergence of a curl is always identically zero.
The curl of a curl of a vector vector field is another vector field.
The spacetime vector has four components, where the time
dimension is multiplied by the speed of light
In Minkowski spacetime, the vector is:
The metric tensor
The
If
If
If
Another, more convenient approach is to make the time dimension complex.
In this case the metric tensor is not required as it is the identity matrix.
Note that the sign is negated and
The total energy of a relativistic body is derived from the rest mass and momentum.
Electromagnetic equations in the SI system contain the
constants
The vacuum permittivity
The vacuum permeability
The electric field vector
The polarisation density vector
The electric displacement field vector
The magnetic flux density vector $ has SI units
The magnetic field strength vector
The magnetisation vector
The current density
The electric potential
We can now compare SI equations with HL equations.
SI | HL |
---|---|
Maxwell’s equations in HL become:
The Lorentz force defines the effect of electric and magnetic
fields on a moving charged particle with charge
Equations can be simplified using potentials.
The scalar electric potential, or voltage, is
The magnetic vector potential
The curl operator doesn’t have an exact inverse. So, any
vector
The electic field vector can also be defined in terms of potentials.