rendered the tensor symmetric by changing Minkowski momentum density from D×BtoE×H/c2 Brevik,s [6] comment on the two tensors was The two tensors correspond merely to different distributions of forces and torques throughout the body. According to minkowski the torque is essentially a volume effect, described by the tensor asymmetry, while according to abraham the torque is described completely in terms of the force density Radiation Pressure The minute pressure exerted on a surface in the direction of propagation of the incident electromagnetic radiation is called radiation pressure. The fact that electromagnetic radiation exerts a pressure upon any surface exposed to it was deduced theoretically by James Clerk Maxwell in 1871, and proven experimentally by lebedev in 1900 and by nichols and hull in 1901 In quantum mechanics, radiation pressure can be interpreted as the transfer of momentum from photons as they strike a surface. Radiation pressure on dust grains in space can dominate over gravity and this explains why the tail of a comet always points away from the Sun The pressure is very feeble, but it can be demonstrated with a Nichols radiometer Consider a laser beam trained upon the black face of one of the radiometer vanes. It will be absorbed(hence the surface looks black). If, before arrival, the light had some associated linear momentum then due to conservation of momentum within the system something else now has to be moving in the direction the light was travelling because the photons have been absorbed and come to a halt. The vane therefore begins to move Now consider the light hitting the shiny side of a vane. The shininess is an indication that the light is bouncing off the surface, which means that it has completely changed direction and is now travelling the other way In this case the momentum imparted to the vane must be twice that imparted when the photon is absorbed, so that the total momentum is conserved Momentum of light Radiation pressure has shown that light must carry momentum. Three different forms of momentum have been discovered 1. Linear momentum: the original form considered in radiation pressure 2. Angular momentum photons can carry an angular momentum of th in the direction of propagation the sign depends on which direction they have been circularly polarised 3. Orbital angular momentum: from changing the position of the wavefront to obtain a spiral beam It is a property of the transverse mode pattern, and each photon possesses In of angular momentum, where I is the number of intertwined helices8 rendered the tensor symmetric by changing Minkowski’s momentum density from D×B to 2 E× H / c . Brevik’s [6] comment on the two tensors was: “The two tensors correspond merely to different distributions of forces and torques throughout the body. According to Minkowski the torque is essentially a volume effect, described by the tensor asymmetry, while according to Abraham the torque is described completely in terms of the force density.” Radiation Pressure The minute pressure exerted on a surface in the direction of propagation of the incident electromagnetic radiation is called radiation pressure. The fact that electromagnetic radiation exerts a pressure upon any surface exposed to it was deduced theoretically by James Clerk Maxwell in 1871, and proven experimentally by Lebedev in 1900 and by Nichols and Hull in 1901. In quantum mechanics, radiation pressure can be interpreted as the transfer of momentum from photons as they strike a surface. Radiation pressure on dust grains in space can dominate over gravity and this explains why the tail of a comet always points away from the Sun. The pressure is very feeble, but it can be demonstrated with a Nichols radiometer. Consider a laser beam trained upon the black face of one of the radiometer vanes. It will be absorbed (hence the surface looks black). If, before arrival, the light had some associated linear momentum, then due to conservation of momentum within the system something else now has to be moving in the direction the light was travelling because the photons have been absorbed and come to a halt. The vane therefore begins to move. Now consider the light hitting the shiny side of a vane. The shininess is an indication that the light is bouncing off the surface, which means that it has completely changed direction and is now travelling the other way. In this case the momentum imparted to the vane must be twice that imparted when the photon is absorbed, so that the total momentum is conserved. Momentum of light Radiation pressure has shown that light must carry momentum. Three different forms of momentum have been discovered: 1. Linear momentum: the original form considered in radiation pressure. 2. Angular momentum: photons can carry an angular momentum of ±ħ in the direction of propagation – the sign depends on which direction they have been circularly polarised. 3. Orbital angular momentum: from changing the position of the wavefront to obtain a spiral beam. It is a property of the transverse mode pattern, and each photon possesses lħ of angular momentum, where l is the number of intertwined helices