Hertz and Radio Waves Explained

Hertz and Radio Waves Explained

and welcome to high school physically explained my name is Paul and I will be going through understanding Hertz’s experiment of 1887 with his discovery of radio waves but before I start let me draw your attention back to 1865 James Clerk Maxwell had predicted that there was a form of wave called electromagnetic wave and he worked that out through combining a number of known laws to do with both electricity and magnetism and in determining the velocity of this electromagnetic wave he came up to a particular value here which ended up being the speed of light which was already determined through other means by number of scientists including Foucault and fuse Oh and as a result Maxwell decided determined that this electromagnetic radiation light was just about one example of and there were other forms of electromagnetic radiation in fact Helmholtz a number of years later actually set up a prize for any scientist who could actually verify Maxwell’s predictions by discovering another form of electromagnetic radiation so how does this work well basically we have here a charged particle and that would vibrate a lot up and down like so and as a result of the vibration of this vibrating particle that would generate an electric field but this same vibrating particle would also generate a magnetic field so what we get here is an alternate a alternating electric field and magnetic field being generated by a vibrating particle and those fields are perpendicular to each other so let’s now introduce ourselves to Heinrich Hertz Heinrich Hertz in 1887 set up and an experiment to show the existence of this electromagnetic wave and what he ended up having is he set up an induction coil with a these balls here which built up a large charge and this area here would produce a small spark and that spark he surmise would generate an electromagnetic wave and because it was a fluctuating electric field and magnetic field it had the potential to cause a charge to flow in this small gap over here in other words create a small spark in this receiver in this diagrammatic version of it over here you can see over here of a simplified version of that spark generator and what happened was it would produce a wave drawn simply like this and a spark over he would generate a small spark over here and as a result that is exactly what occurred and so 100 Hertz are determined that there must be in some sort of wave traveling between the generator over here and the receiver over here so he did a number of experiments with this the first thing he did was he noticed that if he were to place a sheet of metal in between or in terms of the spark generator over here he was able to note that that sheet of metal would reflect our little wave over like so and as a result he showed that this wave was able to be reflected another thing that he was able to do is the show it refracted and so by creating a sort of piece of a triangular prism here in this case out of pitchblende he noticed that when he generated the spark that spark would Bend and as a result he would have to remove his receiver over here to pick up the signal and as a result he showed that he’d actually refracted both properties of course of waves but one of the the most important experiments that he did was he got his sheet of metal over here and he lined it up in such a way that it actually produced standing waves and the thing is that he took his receiver and moved it along the path of where the standing waves were generated and he noticed that he produced large sparks when at this position and no sparks here at all and then successively large barks no sparks large sparks no sparks and then really importantly he was able to determine the wavelength you see the wavelength can be determined by this distance over here and so that distance he over to there is actually half the wavelength of the wave so all of a sudden he was able to determine the wavelength but the natural frequency of the freak of this particular receiver was also known he could determine that and as a result he was also able to determine the frequency of this wave that of course leads to a very important conclusion because the product of these can be worked out and that gives you the speed of the wave but most critically he determined that that speed it actually ended up being the value of C 3 times 10 to the power of 8 meters per second so now all of a sudden the he determined a wave that had the value of C which validated Maxwell’s predictions a number of years earlier but on top of that Hertz also made another important discovery one of the things he noted was that the spark produced over here was particularly weak and so he created a box with a little window and he noticed though the presence of this little window actually weakened the actual spark removing the window made the spark much longer so he surmised that there was certainly some sort of wave adding to the effect of this electromagnetic wave as if to verify it he replaced the window instead with glass with quartz and he noticed that the this window had no effect on the length of the things that actually was not a lot larger in other words the glass seemed to block some of the love the light that was generated over he by the spark and we now know that that was the first observable evidence of the photoelectric effect we now know of course is that this particular spark over here produces not only light but also a small amount of ultraviolet light and the ultraviolet light travelled across at the same speed and as a result excited some electrons on the receiver and therefore gave them a little bit more energy to move a spark and so therefore the spark was was brighter Hertz of course at this stage did not know this but he recorded his observations and certainly suggested further investigation was necessary unfortunately he is work was he was still very interested in electromagnetic induction and further study of radio waves and see he postponed that but unfortunately in 1994 he died and at a very young age of 36 and his work wasn’t again talked about until nineteen hundred and nineteen hundred and five particularly with Einstein’s development of the photo electric effect I hope that gives you an understanding of Hertz his experiment and his subsequent initial discovery of the photoelectric effect please subscribe to my channel and I’ll see you next time Thanks


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