A beam of electromagnetic waves of a wavelength 3.0cm is directed normally at a grid of metal rods, parallel to each other and arranged vertically about 2.0cm apart. Behind the grid is a receiver to detect the waves. It is found that when the grid is in this position, the receiver detects a strong signal but that when the grid is rotated in a vertical plane through 90 degrees, the detected signal strength falls to zero. What property of the wave gives rise to this effect? Account briefly in general terms for the effect described above.
The property of the wave that gives rise to this effect is the polarization. Polarization refers to the orientation of the electric field vector of an electromagnetic wave. In this case, the wave is initially unpolarized, which means the electric field vectors are randomly oriented in all directions.
When the unpolarized wave passes through the grid of metal rods, the rods act as a filter that allows only waves with a certain orientation of the electric field to pass through. The metal rods are aligned vertically, so they only allow waves with electric field vectors oscillating parallel to the rods to pass through.
When the grid is in its original position (with the rods vertical), the unpolarized wave is able to pass through since it contains components with different orientations. As a result, the receiver detects a strong signal.
However, when the grid is rotated in a vertical plane through 90 degrees, the metal rods are now horizontally aligned. This means that the electric field vectors of the wave, which were previously parallel to the rods, are now perpendicular to the rods.
Since the wave now has electric field vectors perpendicular to the aligned rods, it is completely blocked by the grid. As a result, the receiver detects a zero signal.
In summary, the effect described above is caused by the polarization of the wave and the selective filtering of waves with specific orientations by the metal rods in the grid.