Question 9:What is meant by plane polarized light? How do this phenomena decide the light waves are transverse in nature?
The process in which the electric and magnetic vibrations of light waves are restricted in a single plane is called plane polarization and the light thus emerged out is called plane polarized light.
When an electron orbiting around nucleus is excited by any source, it jumps from a lower level to a high energy level. When the source is removed, it jumps back to the lower level and the energy is released in the form of a light wave. When the transition takes place due to an electron orbiting in a vertical plane, the emitted light wave is also polarized in the vertical plane. Similarly, when the transition takes place due to an electron orbiting in a horizontal orbit the emitted light wave is also in the horizontal plane.
The light waves emitted from a source such as a candle or sun is not polarized because it comes from different atoms whose electrons are experiencing the transitions in different planes in all directions. Therefore, light waves received from such sources also have vibrations of electric and magnetic fields in all directions. Various techniques can be adopted to restrict these vibrations in a single plane and the light so obtained is called plane polarized light.
Transverse nature of light
Polarization is the property shown by transverse waves. The longitudinal waves do not have this property. To study this phenomenon, let’s consider a transverse wave set up in a string. Take a wooden block with a large slit P and pass a string in it. We will see the wave in the string passes through it. Use another such wooden block with its slit at right angle to the slit of the first block. We shall see the wave does not pass through it.
On the other hand if a spring with a longitudinal wave is used instead of the string, the longitudinal waves of the spring pass through both the blocks irrespective of their orientation with respect to the one another.
This experiment indicates that only transverse waves can be polarized. So, polarization of light wave provides the evidence that light waves are transverse in nature.