Now if the interaction things with light can be understood in terms of the interactions with the fields, what does the size of the Poynting vector actually mean in practice? Are there any processes that depend on this rather than directly on the amplitude of the electric or magnetic field?Īlthough there is some interesting discussion below, my question has been interpreted slightly differently from what I intended (nevertheless learned a lot though!). Now I always thought (without deeper consideration) that the size of the Poynting vector is proportional to the amount of photons in the EM field, but apparently it is more important to consider the size of the electric field (or maybe the size of the magnetic field in different cases) than the amount photons for many applications. However this is not true for a superposition of plane waves. In this context, one might consider the amplitude of the electric field to be the intensity and indeed this is the same as the magnitude of the Poynting vector for a single plane wave. electronic transitions), the magnetic part is often completely neglected (as the interaction of matter with electric fields is generally much stronger). When considering the interaction with of EM waves with matter (i.e. I always thought of it as the magnitude of the Poynting vector (field), but this is not always correct. The earthquake, which magnitude is higher than 7 on the Richter scale, is highly destructive.I have recently found out that word "intensity" is somewhat ambiguous for electromagnetic waves. The power of an earthquake is expressed in terms of a magnitude and measured on a scale known as Richter scale (as shown in the image given below). The earthquakes mostly are caused by the movement of earth’s plates (as shown in the image below).Įarthquakes are also caused by volcanic eruption/activity, when a meteor hits the earth, or an underground nuclear explosion. The last major earthquake occurred in India on 8 th October 2005 in Uri and Tangdhar towns of North Kashmir and before that a major earthquake occurred on 26 th January 2001 in Bhuj, Gujarat. The major earthquakes are rare, but very much destructive. If a thunderstorm occurs there is also a possibility of lightning and cyclones.Īn earthquake is a sudden shaking or trembling of some region of the earth for a very short time.Īn earthquake is normally caused by a disturbance originated inside the earth’s crust.Įarthquakes keep occurring almost all the time, all over the earth, but most of them are not even noticeable. The metal columns used during the fixing of electrical wires and water pipes in the buildings also protect from the thunderstorm and lightning. The device, used to protect buildings from the effect of lightning, is known as Lightning Conductor.Ī metallic rod, taller than the building, is fixed in the walls of the building from top to toes during its construction protects from thunderstorm (as shown in the image given below). The process of electric discharge also occurs between two or more clouds, or between clouds and the earth (as shown in the image given below).ĭuring the lightning and the thunderstorm no open place is safe.Įlectrical appliances such as computers, TVs, etc., should be unplugged however, electrical lights can be left on, as they do not cause any harm. When negative and positive charges meet, it produces streaks of bright light and sound and the process is known as an electric discharge. The process of transferring of charge from a charged object to the earth is known as earthing. Some natural phenomena can cause large scale destruction of human life and property. When charges move, they constitute an electric current. When a plastic comb is rubbed with dry hair, it acquires some charge and the object is known as charged objects. are the natural phenomena.īenjamin Franklin, an American scientist, showed that the lightning and the spark from clothes are essentially the same phenomena.
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