good day students welcome back to my channel today you will be listening to my mini lecture about the first lesson of the second quarter in grade 10 science by the way this quarter we will be discussing physics particularly the topic electromagnetism in the first lesson i will be talking about the definition properties and forms of electromagnetic waves as well as the scientists who played an important role in the development of the electromagnetic theory [Music] in this lesson we want to compare the relative wavelengths of the different forms of electromagnetic waves but what are electromagnetic waves electromagnetic waves are also called em waves or em radiation the letters e and m stand for electricity and magnetism respectively basically they are created as a result of vibrations and these vibrations create electric field and magnetic fields why do we need to study electromagnetic waves it is because em waves or electromagnetic waves are all around us they are necessary for us to live also most of the technological advances that we enjoy today use em waves the sunlight that we need to see things is an em wave the heat that we enjoy during the summer is also an electromagnetic wave the gadgets that we use now for our distance learning use electromagnetic waves electromagnetic waves have seven types and these types are arranged in what we call an electromagnetic spectrum the seven types as you can see in the diagram below are radio waves microwaves infrared visible light or visible spectrum ultraviolet x-rays and gamma rays you can use the following mnemonic for you to remember these seven terms roman men invented very unusual x-ray guns the first letters of these words would stand for the seven types of electromagnetic waves so we have roman for radio waves men for microwaves invented for infrared very for visible light a neutral for ultraviolet x-ray for x-ray and guns for gamma rays we call visible light visible because it is the only electromagnetic wave that is visible to the human eye tagalog [Music] the rest of the waves are invisible also the seven electromagnetic waves are usually arranged from long wavelength to short wavelength that is from left to right or lowest frequency to highest frequency this means that radio waves with radio waves which is on the left side they have a long wavelength but they also have low frequency while on the right side the gamma rays they will have short wavelength but they have high frequency in short wavelength decreases from left to right while frequency increases provided that started with radio waves going to gamma rays from left to right now let's move on to the different properties of electromagnetic waves first electromagnetic waves are transverse waves last quarter we discussed p waves and s waves the seismic waves where you encounter the terms transverse and longitudinal all electromagnetic waves are transverse the key term here is perpendicular if you remember for longitudinal waves the movement of the particles are parallel to the propagation of the wave here the movement of the particles or the oscillation of the particles are perpendicular to the propagation of the wave next electromagnetic waves are produced by a moving or oscillating charged particle when we say charged particle we are referring to either an electron a negatively charged particle or a proton which is a positively charged particle so if that particle is at rest ibiza being hindigo magalao it will produce an electric field because it is an electric charge however if that particle moves once that particle moves or vibrates or oscillates it will start to produce both electric and magnetic fields so ito electric at magnetic fields atomic combine and they will produce an electromagnetic wave as you can see in the gif on the screen so here we can see that the blue part is the electric field and the yellow part would be the magnetic field and they are perpendicular to each other third they do not require a medium to propagate and they can travel at a speed of 3 times 10 raised to 8 meters per second now let's try to break down these statements first they do not require a medium to propagate okay they do not require a medium to propagate but it doesn't mean that when there is a medium hindinis propagate from one place to another why are we stressing this because if you remember in grade 7 we have what we call a mechanical wave a mechanical wave requires a medium to propagate medium electromagnetic waves propagates when we say medium we are referring to a solid a liquid or a gas so if you have a solid liquid or gas and you have a mechanical wave passing through it a mechanical wave can pass through them an electromagnetic wave will also pass through them however if you have totally nothing you don't have a solid you don't have a liquid or you don't have a gas hindi mechanic electromagnetic wave because it does not require a medium to propagate by the way the term we use for totally nothing or no medium at all is vacuum next part of this property they can travel in vacuum at a speed of 3 times 10 raised to 8 meters per second so in your screen you can see a pictorial representation of the comparison of some speed samples however the units here are not in meters per second say m over s is meters per second okay here the speed is in kilometers per hour and miles per hour however you can see how fast that speed is we are referring to so light is the fastest it is the highest speed possible young speed and lights a vacuum it is the fastest speed possible and scientists haven't discovered any object or any entity that can surpass this spin you nam pinagama bilis so fastest runner ganyalan okay around 43 kilometers per hour and then even the cheetah compared to light napahalayonang difference now how large is 3 times 10 raised to 8 meters per second 3 times 10 raised to 8 meters per second in standard notation would be 300 million meters per second or 300 000 kilometers per second um 0.5 0.8 meters per second normal walking yawn so how fast would be 300 million meters per second it would be very fast according to google the distance between the sun and the earth is 147.13 million kilometers now using the formula for speed which is distance over time we are given the distance from sun to earth and we also are given the speed of light because light is coming from the sun going to the earth if we use this values we will arrive at this time it would take approximately eight minutes for sunlight to reach earth so considering the distance between the sun and the earth it will still take a few minutes for the sunlight to reach our planet next the speed of electromagnetic waves changes depending on the medium where they are passing through a while ago i mentioned that when we say medium we are referring to a solid a liquid or a gas here in the screen you can see that the speed of light in kilometers per second these values will vary depending on what type of material the electromagnetic wave is passing through whether it's solid it's liquid it's a viscous liquid just like oil it's a glass or a different type of solid magibayan speed and generally as you can notice as the solid or as the matter becomes more compact the speed of light decreases so we call this materials optically denser because they are able to slow down light or electromagnetic wave compared to other materials now why are they being slowed down it's because of refraction or bending the more dense or the denser the material the higher the tendency for this electromagnetic waves to bend or to refract index of refraction now let's go on with the qualitative description of the wavelengths of the types of electromagnetic waves and a brief description or brief explanation of their applications so a while ago i have shown this to you okay this is a good representation of the different electromagnetic waves on top of this you can see the different applications so as we can see here radio waves would be used in of course radios am fm and then microwaves would be for cell phones radar and so on and so forth i have here another diagram of the electromagnetic spectrum and it also shows us the relative sizes of the wavelengths i told you last time that the wavelength of radio waves would be longer than the wavelength of a gamma ray okay so san benate wavelength the wavelength of a radio wave can be as stall as a building while the wavelength of a gamma ray can be as small as a subatomic particles you can see the difference of the wavelengths here they can be compared to a baseball to a pinpoint to a bacteria viruses and atoms also here in this diagram the major applications of the electromagnetic waves are shown usually the electromagnetic waves on the right side which are of higher frequency but of shorter wavelength are used in the medical industry but we all know x-rays you use that for imaging we use x-rays also if you know ct scans or other imaging now better than x-rays they use gamma rays so gamma rays can also be used for treatment of cancer infrared ultraviolet and visible light these are three types of electromagnetic waves that can be produced by the sun in it only one egg that is visible light and not only that they will be discussed in the next weeks to come microwaves of course that is used in an oven and also in cell phones also in radars and for the radio waves okay this is used for radios in am stations fm stations they are using radio waves so now let's go to the different scientists who played an important role in the development of the study of electromagnetic theory let's start with william gilbert so william gilbert in 1603 discovered that the earth was magnetic and theorized that electricity and magnetism are not the same so to honor him the unit for magnetic potential gilbert was named after him next we have charles augustine de coulombe in 1785 who formulated what we call the coulomb's law so columns law relates the forces in between two charges and the distance in between them so marantine in a tower attraction and repulsion remember like charges repel opposite charges attract this is similar to magnets because like poles repel and opposite poles attract because of his contribution the standard unit for charge coulomb was named after him so next we have hans christian or stead so in 1820 diba has 200 years young lumipas it was hans christian orsted who finally discovered the relationship between the two fields because before his time electricity and magnetism are two different fields however he accidentally discovered that electricity could produce magnetism while he was teaching his students merosha electric circuit nadine students during that time and he also has a magnetic compass the magnetic compass as we all know samantha seguro it has a needle that moves whenever you move because it follows the direction of the poles of the earth so he placed that magnetic compass in his table when he in gumagala and whenever he switch the circuit on or off slight movement the question is why because unless you move the magnetic compass the compass is just unstable so he discovered there that electricity could produce magnetism next we have joseph henry joseph henry in 1831 is around a decade from the discovery of hans christian orsad discovered electromagnetic induction which is basically the reverse of what was discovered by transcription or stead remember hence christian orders that discovered that electricity can produce magnetism so joseph henry discovered that magnetism can produce electricity and in honor for his contribution the standard unit for inductance was named after him okay however in your henry the problem is that they discovered the same thing at the same time independently hindi almost the same thing which is electromagnetic induction and that is michael faraday so michael faraday also discovered electromagnetic induction which again is a production of electricity from magnetism [Music] next we have wilhelm webber wilhelm edward webber who discovered that the ratio of electrostatic to electromagnetic unit equals the value of the speed of light so from this he discovered that light is an electromagnetic wave another unit was named after him which is the unit 4 magnetic flux [Music] so next in 1861 is james clerk maxwell who formulated four equations which summarize everything about electricity and magnetism [Music] we call these equations the maxwell's equations as you can see now we have four equations here what i'm showing you they are written in differential form but there is also an integral form so both are in the language of calculus and you will notice in number three we have paradise law so this is the reason why i also included michael faraday in the list of the scientists who contributed in the history of electromagnetic wave theory sabiko nina michael faraday is actually more famous than joseph henry and another thing is that james crook actually faraday was mentioned a few times in his book where he published or where maxwell published these four equations next in 1887 we have heinrich schertz who proved the existence of radio waves through his experiments you can remember that the unit for frequency is hertz finally we have albert einstein in 1905 who formulated the concept of photoelectric effect so in this study einstein won the 1921 nobel prize for physics the photoelectric effect is the emission of electrons when electromagnetic radiation such as light hits a material although albert einstein was also well known for his theory of relativity he won the nobel prize for this study so that's all for the history of electromagnetic wave theory i hope you have learned something from this discussion and thank you for listening bye you