Poynting Vector The Poynting vector describes the flow of energy(power) through a surface in terms of electric and magnetic properties. It is the vector product of the electric and the magnetic fields. The Poynting vector points in the direction of propagation of a travelling electromagnetic wave and has the dimensions of power per area The full electromagnetic energy density in a region of space where there are both electric fields and magnetic fields is given by adding up separate contributions from the electric and magnetic fields. This implies energy is stored in the field itself. A unit cube of empty space which contains electric and magnetic fields will have some finite energy. This means electric fields and magnetic fields have a real hysical existence, like particles This energy can also flow around, and the energy current is expressed by the Poynting vector S=ExH Pseudomomentum Despite the temptation to believe otherwise, it is important to remember that it is only by differentiating with respect to the "real"metric that we obtain real momentum. When we differentiate with respect to the analogy metric, we obtain the density and flux of another quantity termed pseudomomentum Nelson [7] notes that momentum is a conserved quantity by virtue of the homogeneity of space, that is, as a result of the invariance of the laws of physics when spatial coordinates are moved. He states that pseudomomentum can also be a conserved quantity provided the medium is homogenous that is the laws of hysics are invariant to translations of the material coordinates In McIntyre's paper [8]on wave momentum, he explains a lot of the controversy as due to people's mistaken beliefs about momentum. He states: Momentum density and momentum flux are independent entities.. fluxes of momentum can perfect well exist in a material medium without there being any momentum". He concludes Abrahams momentum is the electromagnetic contribution to the actual momentum, while Minkowski's is the pseudomomentum There has certainly been no clear understanding of momentum of light in media and at the boundary between media and vacuum. a lot of problems stem from vague definitions -what one physicist means when he states their momentum need not mean the same to another physicist Tensors Tensors provide a formalism that helps to solve and model certain problems more easily. A matrix is a specialised form of a tensor, occupying two dimensions 99 Poynting Vector The Poynting vector describes the flow of energy (power) through a surface in terms of electric and magnetic properties. It is the vector product of the electric and the magnetic fields. The Poynting vector points in the direction of propagation of a travelling electromagnetic wave and has the dimensions of power per area. The full electromagnetic energy density in a region of space where there are both electric fields and magnetic fields is given by adding up separate contributions from the electric and magnetic fields. This implies energy is stored in the field itself. A unit cube of empty space which contains electric and magnetic fields will have some finite energy. This means electric fields and magnetic fields have a real physical existence, like particles. This energy can also flow around, and the energy current is expressed by the Poynting vector: S E H


= × Pseudomomentum Despite the temptation to believe otherwise, it is important to remember that it is only by differentiating with respect to the "real" metric that we obtain "real" momentum. When we differentiate with respect to the analogy metric, we obtain the density and flux of another quantity, termed pseudomomentum. Nelson [7] notes that momentum is a conserved quantity by virtue of the homogeneity of space, that is, as a result of the invariance of the laws of physics when spatial coordinates are moved. He states that pseudomomentum can also be a conserved quantity provided the medium is homogenous, that is the laws of physics are invariant to translations of the material coordinates. In McIntyre’s paper [8] on wave momentum, he explains a lot of the controversy as due to people’s mistaken beliefs about momentum. He states: “Momentum density and momentum flux are independent entities... ...fluxes of momentum can perfectly well exist in a material medium without there being any momentum”. He concludes “Abraham’s momentum is the electromagnetic contribution to the actual momentum, while Minkowski’s is the pseudomomentum”. There has certainly been no clear understanding of momentum of light in media and at the boundary between media and vacuum. A lot of problems stem from vague definitions – what one physicist means when he states “their momentum” need not mean the same to another physicist. Tensors Tensors provide a formalism that helps to solve and model certain problems more easily. A matrix is a specialised form of a tensor, occupying two dimensions