Grade 11 Science – Waves and Their Applications - Revision Question Discussion

[00:04:03]check one. Check one.

[00:04:29]Check one.

[00:04:38]Check one.

[00:04:48]Right. Good evening everybody.

[00:04:51]back again with our online night session regarding a revision kind of a seminar we can tell or revision question discussion from your fourth lesson that is your waves lesson right uh the plan is I have already sent you all a tote from past paper questions and some uh what do you call school paper questions or the okay first term exam questions so we're going to discuss those questions from waves list and meanwhile we are going to summarize and revise waves lesson. We have already completed that lesson in the the class almost about two months 3 months before. So now we are going to do one more revision on that.

[00:05:28]So that lesson is completed 100% complete. Right? Uh before we start confirm me from your end can you all hear me properly and see the board clearly?

[00:05:39]Is video audio everything clear?

[00:05:45]Yes. Yes.

[00:05:47]Right. YouTube right YouTube is also okay perfect now what I want from you all is I'll give you all a summary chart on waves lesson so better to have a uh A4 sheet or maybe a full scap sheet we are going to summarize the waves lesson here I want you all to have a A4 sheet or a full scap sheet or even a CR book behind the CR book somewhere you can write sorry Just get ready with those things.

[00:06:20]Get a CR book or a F4 sheet or a full scrap sheet for us to summarize the lesson. Get ready with the things and send me ready.

[00:06:29]Send me a ready when you are ready.

[00:06:39]Ready? Ready.

[00:06:51]All right.

[00:06:55]Right. Perfect. So, we'll start waves lesson. Waves lesson is unit number four in grade 11. Unit number four, grade 11.

[00:07:04]I have one more update. Later on, I'll tell after about 10 or 20 minutes I'll tell that update as well. So, waves lesson the actual heading is waves and their applications. Right? on we'll summarize we'll summarize when I'm telling these things we have already done these things in the classroom so when I'm telling these things if you know the things try to repeat by your own this is this this is this try to repeat by your own so this is a revision after about two month we are doing a revision we are going to put these things into the brain again one more time and lock it and try some questions so if you know that you already know you have done this already you know the things so whatever you know just try to repeat with me right babes What is a wave?

[00:07:48]A disturbance that propagates energy from one place to another. What is a wave? It's a disturbance. What does it propagate? Energy from one place to another. Does it propagate the particles? Does it totally move the particles from one place to another? No.

[00:08:10]It only propagates the energy from one place to another without the propagation of particles. So when I tell waves, what should come into your mind? It's a disturbance.

[00:08:22]It's a disturbance.

[00:08:24]It's a disturbance.

[00:08:27]It's a disturbance. What does it propagate? It propagates energy. It propagates energy. Does it propagate the particles? Does it move the particles totally from one place to another? No.

[00:08:42]Without the propagation of particles, without the propagation of particles, no particles are propagated. That is a wave. Now, if you take waves, if you take waves, there are there are there are two main types of waves. You know these things. There are two main types of waves. What are the two main types of waves? What are the two main types? One, mechanical wave. Mechanical wave. And two, electromagnetic wave. Electromagnetic wave. Mechanical wave. Electromagnetic wave. Mechanical wave requires a medium to propagate. Mechanical waves require a medium. Now this is a summary note. Now in summarized form we are going to write. So it requires a medium. It needs a medium. Now now now together with me try to write. I won't give separate time for you to write. And maybe you write a sketch note and keep for now. Maybe using a pencil you can write a sketch note and write for now. Later on using color pens all those decor decorative things you can write it separately.

[00:10:04]Okay. For now just write a sketch note with me. Repeat with me. Tell with me.

[00:10:08]Write a sketch note. Mechanical wave requires a medium to propagate.

[00:10:13]Electromagnetic wave do not require a medium. It doesn't need a medium. It do not require a medium to propagate. Now if you take mechanical wave, mechanical waves are again divided into two depending on how it propagates. One transverse wave transverse wave transverse wave and two longitudinal wave longitudinal wave transverse wave.

[00:10:50]Longitudinal wave I'm not going to write the part wave there. Summary note transverse wave longitudinal wave transverse wave what is happening in transverse wave in transverse wave let's take wave is propagating in this direction that is the direction of propagation of the wave then particles present there particles present there will be moving will be moving up and down particles they are moving up and down. Now that's not a standard way of telling this. You can't tell this this way. There's a different way to tell this. Particles they move up and down. Particles are moving up and down.

[00:11:35]What is the angle between the wave propagation direction and particle motion direction? Red color is the particle motion. White color is the wave propagation.

[00:11:49]Red color is the particle motion.

[00:11:51]Particle motion is red color. White color is the white color is the wave direction. What can you tell about the angle between the wave direction white line and the particle motion direction red line? What can you tell? What's the angle there?

[00:12:09]90°. That means I can tell that means I can tell particle motion is perpendicular to the wave motion.

[00:12:18]Particle motion perpendicular to the wave motion transverse.

[00:12:25]Particle motion perpendicular to the wave motion that is transverse wave.

[00:12:28]What are the examples for transverse wave? What are the examples for transverse wave? Water wave. Water wave and motion of a plucked string in a guitar. You play the guitar. When you play the guitar, the string there, the string there will be moving up and down.

[00:12:50]String there will be moving up and down.

[00:12:52]Meanwhile, the wave will be propagating in a certain direction. So motion of a plucked string in a guitar. Motion of a plucked string in a guitar. Summary note, we'll just write it as plucked string. Plucked string.

[00:13:07]Plucked string round.

[00:13:12]Next going to longitudinal wave. Next going to longitudinal wave. What is longitudinal wave? In longitudinal wave, if the wave is traveling in this direction, if the wave is traveling in that direction, then then the particles there particles there will be moving will be moving forward and backwards forward and backwards. That is the particle motion. Red color is the particle motion. Red color is the particle motion.

[00:13:56]Now look at the red color line. Red color is particle motion. Look at the white color line. White color is the wave motion. What can you tell about the wave motion? White line and the red line. Particle motion. Both are both are parallel. So the key word here is key word here is I write the keyword parallel. That's the key word. So what's the key word here? What's the key word here? We'll write that also. What's the key word here? Here the key word is perpendicular.

[00:14:29]Perpendicular is the key word. Underline key perpendicular. Here parallel is the key.

[00:14:39]So if the wave is moving this direction, particles will be moving forward and backwards.

[00:14:45]You can actually learn these wave motion using a slinky.

[00:14:50]I should have a slinky. Give me a second. I'll bring the slinky.

[00:15:40]Why are they in a slinky?

[00:15:43]In the the classes I have shown you all this long spring like thing is the slinky spring slinky. So using a slinky we can study wave motion. So if I show you transverse wave I I I actually keep it on a table and show I can't do it that way. If I show you transverse wave in transverse wave wave is moving this direction.

[00:16:08]Particles are moving up and down. See wave is moving that direction.

[00:16:14]Particles are moving up and down.

[00:16:18]That is a transverse wave.

[00:16:23]That is a transverse wave.

[00:16:26]This trans if I show longitudinal wave in longitudinal wave particle motion and the wave motion are parallel.

[00:16:36]This is a longitudinal wave.

[00:16:41]This is longitudinal thing. See particle motion, wave motion are parallel that is longitude.

[00:16:53]Now when these what do you call the the springs they are come together when they clump up together when they clump up together see they are clumping up together. When they clump up together you call you call you call. When they clump up together you call. What is formed? Try to tell the name. We did this all the in the class.

[00:17:18]When the spring particles clump up together, when the spring clumps up together, joins together, you call what?

[00:17:26]Uh you call it a compression. When they come together, it's a compression.

[00:17:33]When they come together, it's a compression. When they separate a side, when they go far away, when they go far away, you call it a refraction.

[00:17:43]You call it a refraction. So when the spring comes together and compression, compression, refraction, compression, refraction, compression, refraction, compression, refraction. That is how the wave will propate. Compression and refraction. What is the example for longitudinal wave?

[00:18:04]Sound wave. Sound wave is a longitudinal, right? So that is mechanical wave. Going to electromagnetic wave. Electromagnetic waves do not need a medium. They do not need a medium. If you take electromagnetic wave, in electromagnetic wave there are two waves that are oscillating together. In electromagnetic wave there are two waves oscillating together. If I draw and show you all.

[00:18:32]Let's take this is the this is the direction of propagation.

[00:18:42]That is the direction of propagation.

[00:18:46]If that is the direction of propagation in electromagnetic wave you have electrical wave. You have electrical wave. Let's take that axis is the electric wave.

[00:19:01]as well as you will have the magnetic wave. Let's take magnetic wave is coming out and going in. This is the magnetic wave.

[00:19:12]That's the magnetic wave. So if I draw and show if the direction of propagation is like this, electric wave will be going in this axis. Blue color is the electric wave.

[00:19:26]Meanwhile, magnetic wave will be coming out and going in. It will be coming out and going in only that is magnetic.

[00:19:49]This is electric wave. Blue color is electric wave.

[00:19:58]Blue is electric waves.

[00:20:02]Red is the magnetic field. That's the magnetic wave.

[00:20:10]There you go. That's the magnetic field.

[00:20:12]So if electric wave travels in this axis, magnetic wave will be coming out and going in. Coming out and going in.

[00:20:20]Now think 3D. Electric wave traveling in this axis. Magnetic wave travels out and in. Out and in. Now connect them together. Electric wave travels in this axis. Magnetic wave like this. Electric wave this axis. Magnetic wave like that.

[00:20:36]So that is how the electric and magnetic wave will be both are connected together both oscillating together. That is electromagnetic wave. Does it need a medium to propagate? They don't need a medium.

[00:20:50]What can you tell about the angle between electric wave and magnetic wave?

[00:20:56]What can we tell about the angle between the electric wave and magnetic wave? The axis of electric wave and magnetic wave.

[00:21:02]Remember axis of electric wave and magnetic wave are perpendicular to each other 90°.

[00:21:10]What can you tell about the angle between electric wave and the direction that is also perpendicular?

[00:21:18]What can you tell about the angle between magnetic wave and the direction that is also perpendicular? So all three are perpendicular to each other.

[00:21:28]Electric wave axis, magnetic wave axis, direction axis, all three are perpendicular to each other. That is how it is propagated.

[00:21:37]As all three are perpendicular to each other, detail electromagnetic wave is having the properties of transverse wave. That's the important point. As electromagnetic wave, electric wave axis, magnetic wave axis, direction axis, all three are perpendicular to each other. We tell it has the properties of the transverse state. Why? We tell it has the properties of the transverse wave. Go tell me now in transverse wave what is the key word we have? What's the key word in transverse wave? Perpendicular.

[00:22:16]Here also can you see electric wave direction, magnetic wave direction and the direction of propagation all are again perpendicular.

[00:22:29]Transverse wave also all the both both the components they are perpendicular.

[00:22:34]In electromagnetic wave all the three components are perpendicular. Therefore we tell electromagnetic wave shows the properties of transverse wave. It has the connection with the transverse wave.

[00:22:45]I don't tell this is transverse wave.

[00:22:47]You can't keep them closer. Transverse wave need a medium rubber gate.

[00:22:51]Electromagnetic wave do not need a medium rugate. So from the base definition they are separated. But with the angle definition yes they show some similarity. Electromagnetic wave the three components are perpendicular.

[00:23:03]Transverse wave the two components are perpendicular. So I can tell electromagnetic wave shows the properties of the transverse wave right when you take electromagnetic wave there are so many electromagnetic wave with which we form the spectrum.

[00:23:18]What is the spectrum? If I write the spectrum there electromagnetic spectrum there I will start from high frequency to low frequency. High frequency you start with gamma rays.

[00:23:30]gamma rays. Second, x-ray.

[00:23:35]Next, ultraviolet radiation. Next, visible light.

[00:23:42]Visible light.

[00:23:44]Next, IR, infrared radiation. Next, microwave. Microwave.

[00:23:52]Finally, radio wave. Radio wave. All these are electromagnetic wave. When all these electromagnetic waves are arranged in this kind of a order or maybe in the reverse order you call that a electromagnetic spectrum. This is a electromagnetic spectrum. It has all the electromagnetic waves. Now if you look at these waves from gamma rays to the radio wave from gamma ray to the radio wave from this side to that side what is happening to the frequency?

[00:24:27]Frequency is reducing.

[00:24:30]When frequency reduces, what happens to the wavelength? Automatically wavelength will increase. What is this symbol? It's a Greek symbol. In Greek, you call it what?

[00:24:44]We have a constant number. Now I allow you all to unmute.

[00:24:50]So see that you all have I on the mic featur >> the lambda symbol >> in science or in wave section we use it to represent the wave length. So this is frequency that's wavelength. Frequency decreases wavelength increases. So gamma has the highest frequency, radio has the lowest frequency. That's why radio is very stable. You can use it to transmit any information.

[00:25:26]Gamma is unstable. Why frequency is very high. Meanwhile this side to that side wavelength increases. So radio waves have a longer wavelength. Long distance communication you can use radio waves.

[00:25:39]Camar have a very short wavelength, very short wavelength. So you can't use it for communication. Actually these three you can't use for communication. Those three are high frequency high energy. If you want to do anything related to high energy use gamma x-ray UV and that also highest energy is gamma and using that you can kill living organisms.

[00:25:57]Microorganisms can be killed. So you can use it for sterilizing. You can kill cancer cells. So for cancer treatment gamma rays are used. Why high frequency?

[00:26:05]No high energy. Think like high frequency destroyers. So gamma is destroyer. It will destroy the cancer cells. It will destroy any microism. So use for sterilizing. X-ray again high frequency. High frequency. It can penetrate. It can penetrate through our soft tissues. It can't go through our bones. Therefore, it is used to take X-ray photographs. It can penetrate through our the baggage bag, but it can't go through any metallic object inside. So it is used for scanning the bagages. X-rays. UV ray ultraviolet radiation. It has a frequency slightly above the violet. used to check bank nodes. Sun gives us UV. Uh UV helps to produce vitamin D in our skin. Visible light the light that we have. IR radiation. IR radiations are used in remotes. Remotes for short distance communication. Now this side is communication. This side is communication. IR is for short distance communication. Now the LED in front of the remote, it emits IR. With our normal eye, we can't see that. But a camera can see.

[00:27:09]See camera can see that.

[00:27:36]How do I put that camera if I see it with the I can't see that camera can see that that is radiation in the class I have shown these things magic these are normal things.

[00:27:58]Sorry right that is IR radiation for short distance communication so used in um the the TV remotes for short distance communication also it's used in physiootherapy treatment another name is there for IR radiation you can also call it what waves waves Heat rays.

[00:28:29]>> Heat waves because hot object, heated objects emit IR radiation, right?

[00:28:34]Microwaves little long distance communication compared to IR little more long distance. Mobile phones, phone to the nearby tower. When you make a call, the call goes from the phone to the nearby tower as what? Microwaves. Even in microwave ovens, you have microwaves.

[00:28:51]What is a device that generates microwave?

[00:28:55]Inside the oven there's a device that generates microwave. What generates a microwave? Produces microwave.

[00:29:00]>> Magnetone. Magnetone.

[00:29:02]>> Magnetone. Magnet.

[00:29:06]If you have forgot those things, write those things. That's what you call revision. Microwave.

[00:29:12]Uh the device that produces microwave is magnetron.

[00:29:17]Magnetron. And radio waves. Very long distance communication. Very long. Maybe a tower to a satellite. satellite to a tower very long distance communication radio waves right um radio waves are emitted by what what's the device that emit radio wave now microwave is emed by mag radio who can remember h radio frequency oscillators radio frequency oscillators just keep those things in mind radio waves are emitted by radio frequency oscillators it's received by what can receive Radio waves.

[00:29:57]What you have on top of your TV? What you have outside? What is that?

[00:30:03]>> Antenna. Received by antenna. This is received by antenna.

[00:30:11]That's about the wings initial things.

[00:30:16]You want to take a screenshot? Take a screenshot. If you couldn't write the sketch with meal, take a screenshot.

[00:30:28]What I mean by RF is I short radio frequency oscillator.

[00:30:33]You all don't write RFO. There's no word called RFO. I wrote it in short. Radio frequency oscillator is RFO.

[00:30:45]Sorry. Right. Next about the physical quantities. Like what you have to learn is these basic things. physical quantities and about sound any question you can do remember waves lesson is a very simple lesson if you get a question from waves le exam you should be happy first thing that you should do is you should be happy about it because that's the easiest section where you can get questions and where you can scope so next about the physical properties physical properties now if you take away If you take away summary note right let's take this is the displacement of the wave displacement ment of the particles in the wave and this is the distance the wave is traveling distance the wave is traveling yaxis is the displacement of the particles in the wave x-axis is the distance that the wave is traveling now if I draw a wave there what are the properties we analyze here one this is the maximum displacement of the wave maximum displacement of the wave what is this maximum displacement of the wave called as what is letter Okay.

[00:32:18]Amplitude.

[00:32:20]Maximum displacement of the wave is the amplitude. Maximum displacement of the wave is the amplitude. Next, this is a length of a wave. That's the length of a wave. Length of a wave is what you call as wavelength symbolized by lambda.

[00:32:37]Lambda is wavelength. Length of a wave.

[00:32:41]Lambda. Lambda is the wave length.

[00:32:44]Right. Next. This is the This is the maximum point in a wave.

[00:32:51]Maximum point in a wave is open the mouth and tail. You have done >> maximum point in a wave is the crest.

[00:33:01]This is the minimum point of a wave.

[00:33:03]Minimum point of the wave is >> that's the crest. That's the rough. This is amplitude. That's the wavelength. uh next same thing but we do the analysis for a different type of graph.

[00:33:21]Now I'm going to take again my y-axis.

[00:33:26]My y-axis no change as the displacement axis. y-axis no change displacement axis. X-axis I'm going to take as the time axis. Before I took it as distance that the wave is traveling. How long the wave is traveling. Now I'm going to tell how how much time is taken for the wave to travel. So I drew a wave.

[00:33:52]This as previous that's the amplitude maximum point just like the previous one it's crest minimum point like the previous one it's the trough now if I take this go tell me is it a distance measurement you know x-axis is this a distance measurement before it was a distance measurement now is it distance measurement >> oscillation >> uh hurry what is that measurement put what is there on the x-axis time measurement now that measurement is time measurement >> so what is that it's the time taken for one oscillation can you see that this is one oscillation one wave time taken for one wave is what I marked in yellow >> time taken for one wave time taken for one full wave is called as what time?

[00:34:53]>> Period.

[00:34:54]>> Period. Or you call it the periodic time. Period. Time taken for one full wave is period. Uh in standard we measure it in seconds.

[00:35:04]>> So can we say wavelength?

[00:35:07]>> It can't be wavelength. Why? Why? Now is it the length? Is xaxis length measurement? Take a time measurement.

[00:35:14]Length measurement is time measurement.

[00:35:16]I have changed the x axis. So that is the time time see x a is the time time taken for one full wave. Time taken for one full wave is the period measured in seconds. That is time taken for one wave. If I write it here time for one wave time I'll write it in short. Time for one wave what is given in your book is time for one oscillation. Oscillation and wave are same. Time for one wave is period. Now we have the opposite of this. Next one. Next on we define something called frequency.

[00:35:55]We define something called frequency.

[00:35:56]Simple f. Simple f is frequency.

[00:36:00]Frequency. The unit is hertz. Another unit is there. What the other unit? Who can remember the other unit?

[00:36:09]Second oscillations per secondh oscillations cut it off per second. Per second s the power minus one. Two units are there. Not only hertz per second s the minus one. Another unit for frequency. So frequency can be measured in hertz or per second. Now what is frequency? Is the opposite of period.

[00:36:33]What is frequency?

[00:36:36]Number of waves.

[00:36:39]Number of waves. What is given in your books is oscillation.

[00:36:43]Number of waves in 1 second.

[00:36:48]Number of waves in 1 second. Can you see it's the opposite there? Before time for one wave.

[00:36:57]Now number of wave in 1 second.

[00:37:02]Before wave became one, you calculated the time. Now time become one, you calculate the number of waves.

[00:37:14]It's the opposite. Before wave became one, you calculate the time. Now wave, now time becomes one, you calculate the waves. It's the opposite. It's the direct opposite. See, before wave became one. Now we are calculating the waves.

[00:37:37]Before time you calculated now time we are defining as 1 second. So it's the opposite period time taken for one way frequency number of waves in 1 second. It's the opposite as it is the opposite. As it is the opposite, we can make we can make a mathematical equation connection. We can make a mathematical equation connection.

[00:38:04]What is the equation connection?

[00:38:06]Remember frequency is the reciprocal of period.

[00:38:13]Frequency is the reciprocal one over period. F is equal 1.

[00:38:19]First equation in this lesson frequency is equal to 1 /. So if period is given you can calculate the frequency same way if frequency is given also you can calculate the period can when this is given can't you calculate this max can or when the other side is given when this is given you can calcate this so frequency is the reciprocal of the be first equation second equation we can calculate the speed of a wave speed symbolized as v speed of a wave is equal to v is equal to frequency V multiplied by the wavelength lambda. V= F lambda.

[00:38:57]You multiply the frequency by the wavelength, you can calculate the speed of a wave, how fast the wave is moving.

[00:39:04]H those are the physical quantities.

[00:39:10]Sorry.

[00:39:15]Those are the physical quantities.

[00:39:25]Now after writing a sketch note nicely make a nice beautiful note and maybe send it to me so I can leave it in the group as well useful for the others.

[00:39:35]Take a screenshot those who want right.

[00:39:51]Finally we have to learn about sound.

[00:39:56]Sound sound uh under sound you have to learn about the characteristics of sound. Sound has three characteristics. What are the three characteristics of sound? My dear students tell me my dear students loudness loudness.

[00:40:24]>> Loudness. These are characteristics.

[00:40:26]>> Quality of sound.

[00:40:27]>> Quality of sound.

[00:40:28]>> Quality of >> quality of sound.

[00:40:33]Now revise with me. Quality of sound.

[00:40:36]Again you are not going to learn all these things. One time done. It is done.

[00:40:40]Again you touch this section in your level. Put it to the mind. Now it's pitch. Pitch depends on the >> frequency.

[00:40:47]>> Frequency.

[00:40:48]>> Frequency.

[00:40:48]>> Now we know already what is frequency.

[00:40:50]What is frequency? Time taker for one.

[00:40:53]How much of sorry number of waves in 1 second frequency number of waves in 1 second. So pitch depends on the frequency.

[00:41:01]When the frequency increases on pitch will also increase. When frequency increases pitch will increase. Now what is actually this pitch means highness of the leness of the sound. Now for example this is high pitch sound.

[00:41:18]This is low pitch sound. High pitch, low pitch. That's the difference.

[00:41:25]High pitch, high frequency. Low pitch, low frequency.

[00:41:33]Okay. Girls usually talk in what pitch.

[00:41:38]>> High pitch.

[00:41:39]>> High pitch. Girls usually they they talk in high pitch. Boys usually talk in the larynx enlargement low pitch. base voice.

[00:41:53]Next, loudness. Loudness depends on the >> amplitude of the sound.

[00:42:00]Amplitude.

[00:42:03]Amplitude. This part amplitude of the sound. Same way when the amplitude increase loudness will increase the sound become loud. When the amplitude decreases, loudness decreases.

[00:42:17]Quality of sound depends on the nature of the wave.

[00:42:26]Wave nature. Wave nature depends on wave nature.

[00:42:33]Wave nature means how the wave is. Now this wave will produce a certain sound.

[00:42:38]Now maybe this wave will produce another different sound. That's the wave nature. This wave produces one sound and this wave produces another sound. That is the wave nature. When wave nature changes the quality of the sound will also change.

[00:42:55]Next speed of sound.

[00:43:14]Simple.

[00:43:16]Speed of sound.

[00:43:20]Speed of sound depends on what? Speed of sound. One, it depends on the medium of propagation.

[00:43:32]How does it depend on the medium of propagation? In gaseous medium, speed of sound is low.

[00:43:41]In liquid medium speed of sound is average short form short form again after one month you turn this you can't remember what is gi medium speed of sound is low liquid medium there's average speed for the sound in solid medium speed of sound is very high so speed of sound one it depends on the medium of propagation in gasous medium speed of sound is low liquid medium speed of sound is average solid medium speed of sound is high. If I give example in air, who can remember the speed of sound? Can anybody remember speed in air?

[00:44:21]>> 330 ms 300 330 m per second.

[00:44:25]>> In air 330 m in liquid somewhere around 1,400 m/ second you can round it off to,500. In solid in steel 5,000 m you see depends on the medium. Now specifically if you take gasous medium air mainly air in gaseous medium in gaseous medium listen in gaseous medium speed of sound also depends on the temperature and the humidity.

[00:45:02]When the temperature increase speed of sound will increase. When the temperature decrease, speed of sound will decrease. Now, for example, speed of sound in AR is 330 m/s. That is at 0°.

[00:45:19]At 0°C, only speed of sound is 330 m/s in air.

[00:45:27]Same if the temperature is 30° C, now the speed of sound will be 350 m/s.

[00:45:36]0 330 350. So when temperature increases speed of sound will increase as well as humidity. Humidity is the amount of moisture in the envir when the moisture changes speed of sound will change. How it changes you don't need actually these values of dry air.

[00:45:57]Why we tell dry air? There is no humidity. There's no moisture. In case if there is moisture these values will change.

[00:46:04]All right. Remember speed of sound in air only depends on speed of sound in air that is actually gas. Speed of sound in air only depends on we don't send the sound through hydrogen gas or helium gas.

[00:46:27]Speed of sound in air only depends on temperature and humidity.

[00:46:34]Does it depend on pressure?

[00:46:36]No. Does it depend on frequency?

[00:46:42]No. Does it depend on wavelength?

[00:46:46]Again, remember speed of sound only depends on temperature, humidity. Now I know some fellows will tell sir sound depends on frequency. Sum depends on wavelength.

[00:46:58]I I gave a equation v= f lambda.

[00:47:04]Just imagine if frequency increases or anything mathematically speed will increase. Neither frequency increases speed should increase. No other speed of sound depends on frequency.

[00:47:18]This is what is happening. How do you think I understand your logic? When frequency increases, speed of sound will increase. But remember when frequency increases automatically wavelength will decrease.

[00:47:32]this side increases which will result in the increase of the speed but automatically wavelength is decreasing. Now tell me when wavelength decreases what level of speed of sound?

[00:47:42]When one factor decreases what speed of sound decreases.

[00:47:47]See one factor is trying to increase the speed another factor is trying to decrease the speed. Now tell me will the speed change one factor is trying to increase the speed. Other factor is trying to decrease the speed. Now will the speed change?

[00:48:03]>> No.

[00:48:03]>> No.

[00:48:07]When you try to increase the frequency, yes, speed will try to increase but automatically wavelength will decrease.

[00:48:14]The speed will decrease. One factor is trying to increase, the other factor is trying to decrease, then speed won't change. Tell me does the speed does the speed depend on frequency? No. And the speed of sound does the speed of sound depend on wavelength.

[00:48:31]It doesn't depend on speed. Frequency doesn't depend on wavelength. Why? If you increase this this side will decrease and make it constant.

[00:48:38]Remember speed of sound in air only depends on only depends on what temperature.

[00:48:45]And uh regarding the hearing range, what is the normal hearing range of human >> 20 Hz to 20,000 Hz that's the hearing range of human any sound above this 20,000 Hz is called as what sound?

[00:49:16]>> Ultra.

[00:49:17]>> Ultra sound. Ultra sound.

[00:49:18]>> Ultra sound. Can human hear can human ear hear this?

[00:49:23]>> No. No.

[00:49:24]>> But tell me some animals who can hear this.

[00:49:28]>> Bat rabbit rabbit.

[00:49:34]>> Rabbit. Sounds below this frequency is called as what sound?

[00:49:40]>> Infra sound. Infrasound.

[00:49:43]Sound. Tell me animals who can hear infrasound.

[00:49:50]>> Elephant can detect infrasound. Now if you take dogs, dogs can hear up to 40,000 hertz. Backs can go up to as I can remember about 80,000 htz. 80,000 75,000.

[00:50:01]Those are their ranges. Now tell me a property of ultrasound. The making I'm asking tell me a property of ultrasound.

[00:50:09]Tell me something about ultrasound. What can you tell?

[00:50:16]These are on think property don't need to think a lot >> about 20,000 property ultrasound is about 20,000 tell me a property of infrasound >> below 20 >> below 20 >> property of ultrasound is about 20,000 Hz property of infrasound is below 20 tell me ultrasound is transverse wave longitudinal wave electromagnetic >> wave electromagnetic electromagnetic >> longitudinal wave tell me sound is what the sound that we can hear now I'm talking this sound is >> sound is what Sounditude.

[00:51:17]Sound is longitudinal.

[00:51:19]How come ultrasound is electromagnetic?

[00:51:23]What is ultrasound? Just the frequency is high. Just that human can't hear.

[00:51:28]Just because human can't hear, will it become electromagnetic?

[00:51:33]Just because you can't hear, are you going to tell it's electromagnetic?

[00:51:37]>> No.

[00:51:38]>> What is ultrasound? just the frequencies of let's take 21,000 Hz and ultrasound electromagnetic if 20,000 Hz is longitudinal now how how it becomes 21,000 is electromagnetic and that's wrong remember ultra sound hearing rate sound infrasound all sound are longitudinal again I repeat ultra sound sound I'm not talking about ultraviolet radiation Ultraviolet radiation is a different story that's electromagnetic. I'm talking about ultra sound ultra sound hearing range sound infrasound all sound all sound that you hear that you don't hear all sound is longitude >> so I can tell another property of ultrasound they are longitudinal waves another sound of infrasound they are longitudinal waves I think No need to do tell me what are three types of music instrument while taking the screenshot you all talk to me. What are three types of musical instruments instrument?

[00:53:05]>> Yeah.

[00:53:06]>> Ring instruments is there. Sita all those things and wind instruments are there >> winding >> right now go to the paper the T that I posted again don't keep this lesson to study done today it's done this is 2018 O level paper the setup of apparatus range to study about sound wave is given In the figure control key, signal generator, signal amplifier, loud speaker, sound what are the questions everything all those details are given. I'm lazy to read them but when you all are reading read it Roman number one indicate in hertz the frequency range that has to be maintained to make the sound received from loudspeaker sensitive to human ear.

[00:54:01]What's the range sensitive to human ear?

[00:54:04]20 Hz to >> 20 Hz to 20,000 >> 20,000 >> go 20,000 20 Hz to 20,000 Hz number two Roman what is the characteristic that changes in the sound her when the frequencies gradually increase within the above range when frequency changes what changes >> pitch what is the characteristic of sound that changes when the amplitude is changed When you change the amplitude, what will you change?

[00:54:36]>> Loudness.

[00:54:37]>> Loudness.

[00:54:37]>> Loudness.

[00:54:38]>> Loudness.

[00:54:40]>> Roman four. The sound emitted from the loudspeaker travels through sound detector through AR as a mechanical wave. We know that. No, you don't need to tell. We know. Question. To which type of wave does this mechanical wave belong to? Sound wave is which type of the mechanical wave?

[00:55:02]Write it.

[00:55:05]be explain briefly the behavior of air particles in the medium when this wave travel now some fellows are more scared when they see this word explain think big tell about longitudinal wave you all know you all know how to tell lies tell some lies about longitudinal waves what we can tell longitudinal wave particle propagation is per sorry parallel to the wave propagation That is the behavior. Now here they asking air particles. Air particles movement is air particle propagation is parallel to the wave motion. So write down quickly write down air particle propagation. Air particle motion write air particle motion.

[00:55:53]Air particle motion is parallel is parallel to the wave motion to the wave motion.

[00:56:14]Okay. Roman five when the experiment was conducted keeping the detector at a distance and the distance is given 170 m from the loudspeaker the sound emitted from the loudspeaker took.5 seconds to reach the detector we have two information I'll just write it separately distance is given 170 m time is given.5 seconds distance is there 107 m time is given.5 seconds are okay what are they asking question A calculate the velocity of the sound in air calculate the velocity of the sound in Yeah.

[00:57:25]Calculate the velocity of the sound in air.

[00:57:30]All right.

[00:57:32]So now I have the distance 170 m. I have the time 0.5 seconds. They are asking the velocity.

[00:57:40]Distance is there. Distance here.

[00:57:42]Displacement may be the same. Time is 0.5 second. They are asking the velocity. Go tell me I have the distance. Distance can be treated as the displacement here. Roman 5 a distance is the displacement here. Time is there. They asking velocity. By the way, what's the equation you know about velocity?

[00:58:06]distance that's the disment there and time >> you know the displacement what's the displacement 170 m you know the time time is.5 seconds some fellows are scared to do this calculation now you should be able to do this calculation 170.5 170.5 170 by half 170 by half is two times of it. How much? 3 >> 40 >> 340. What's What's the unit?

[00:58:46]>> M/ second.

[00:58:48]>> 340 m per second. That's your answer.

[00:58:50]That's it.

[00:59:03]Huh?

[00:59:05]B state with the velocity of sound changes or doesn't change. That's it.

[00:59:11]They're asking changes or doesn't change in the instances Roman one and Roman two below. Changes or doesn't change.

[00:59:17]Changing the frequency of the signal.

[00:59:20]Now tell me they're asking state with the speed of sound. Velocity of sound speed of sound changes or doesn't change. Now sound is traveling where?

[00:59:28]What is the medium here? It's traveling in air. They are not doing the experiment in water or any other solid thing. They're doing it in air. So they are talking about speed of sound in air.

[00:59:38]Question.

[00:59:40]State whether the velocity of sound does the speed of sound changes or doesn't change. Frequency. Go tell me when you change the frequency does the speed of sound change?

[00:59:49]>> No.

[00:59:50]>> No.

[00:59:50]>> No. Doesn't change.

[00:59:52]>> The answer should be doesn't change.

[00:59:56]>> Doesn't change. Change.

[01:00:02]Changing the temperature of air >> does change >> change.

[01:00:13]>> That's it. Even they not asking whether it increase or decrease asking whether it changes or not. That's it. 2018.

[01:00:23]>> Next part structure question is there.

[01:00:26]Consider the following types of waves.

[01:00:28]UV, IR, micro, X-ray, gamma, visible sound, ultrasound. Roman one. Of the above waves, mention a wave that propagates with compressions and refractions. Compressions and refractions should be a longitudinal wave. Longitudinal Q1. What should come to mind?

[01:00:44]>> Sound with another answer you can write.

[01:00:47]You don't need to write it.

[01:00:52]>> You can write. No problem.

[01:00:54]Either you can write sound wave or you can write ultrasound ultraviolet ultraviolet ultrasound they are just asking one write down a special characteristic of ultrasound characteristic of ultrasound is about 20,000 hertz.

[01:01:29]I can't write on these lines. You all write up. Frequency is above 20,000 hertz.

[01:01:35]Frequency is about 20,000.

[01:01:40]Roman three. In the field of medicine, which type of the above wave is generally used to observe the conditions in the fetus inside the womb of a pregnant mother to scan the womb? What?

[01:01:50]What? What's the way?

[01:01:56]damage will cause any problems on the fetus. So it's ultrasound ultrasound scanning problem four a part of the electromagnetic spectrum is given below.

[01:02:11]First we analize A visible light ultraviolet ray C gamma rays. Now I gave you in the opposite way I started gamma this site. Can remember my one.

[01:02:25]I started in what order? I I started I I wrote it in uh decreasing frequency order. Gamma radio. This side I wrote they given it in the other way. Increasing frequency order.

[01:02:49]So I have written it in decreasing frequency they are giving it in increasing frequency one I I'll write it from this side gamma we'll write it in the decreasing frequency itself gamma after gamma next what >> xray >> xray >> xray >> c should be x-ray uv is there visible Visible is there after visible what?

[01:03:16]>> Infrared >> infrared.

[01:03:21]>> After I microwave >> microwave >> microwave.

[01:03:30]Question A. Consider in the sequence of the above wave. Write down the type of wave that should be in the places A B C.

[01:03:38]A micro B I R C X-ray.

[01:03:49]>> So A micro >> B I R C X-ray.

[01:03:55]All right. You want you write the full form. Infrared radiation.

[01:04:02]B part. A waveform relevant to gamma rays are given below.

[01:04:09]Right? Okay. By which name the point R of the wave can be identified. This is R. Go tell me lowest point in a wave is called as what?

[01:04:19]>> Truff.

[01:04:24]>> Roman. Which physical quantity of the wave is equal to the distance between the point P and Q? Wavelength wavegength >> of the wave P and Q. This distance is what distance?

[01:04:40]>> Wavelength.

[01:04:43]>> Now I gave you distance.

[01:04:47]If this distance is wavelength, I can tell even this distance is wavelength. How many?

[01:04:57]Even this distance is wavelength. They all will have the same length.

[01:05:02]Even this distance is wavelength.

[01:05:06]Even this distance is wavelength.

[01:05:10]So they all can be the wavelength distance. So that's what they asking.

[01:05:14]They asking from crest to crest. Crest to crest distance is however wavelength.

[01:05:25]Roman three. Consider the features of the waveform given above for gamma rays.

[01:05:30]Draw a typical waveform in the following grid. For the type of wave represented by C in the spectrum above when the amplitudes are equal. Again read it slow. Considering the features of the waveform given above for gammar. Now this is gamma array. Here they have told this is for gamma array. Draw a typical waveform in the following grid for the type of wave represented by C. What is T? C is Xray. Now what's the difference between gamma and X-ray?

[01:06:06]>> X-ray is wavelength is shorter.

[01:06:09]>> Wavelength is short, frequency.

[01:06:12]>> Ah here frequency more here frequency less.

[01:06:18]wavelength X-ray wavelength is high gamma wavelength is less that's the difference frequency reduces wavelength increases so extreme of frequency decreases wavelength increases right okay what are they asking the features of the waveform given above for gamma rays draw a typical waveform in the following grid for the type of wave represented by C now they're asking to draw for X-ray see in the spectrum above when the amplitudes are equal both the amplitudes are equal so what is going to change the frequency should be now less but wavelength should be more we can't represent both of them so what we represent is you can represent the frequency there right so here look here now you have to exactly measure the number of boxes and row amplitude 1 2 3 4 F four box is amplitude. Four box they have taken for amplitude. Wavelength 1 2 3 4 5 6 7 8. Eight boxes for the wavelength they have taken.

[01:07:31]1 2 3 4 is the amplitude. 1 2 3 4 5 6 7 8. Eight boxes for the wavelength they have taken.

[01:07:40]So here if I redraw it for Xray.

[01:07:46]1 2 3 4 5 6 7 8. You count and row that.

[01:07:51]1 2 3 4 5 6 7 8. 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8.

[01:08:06]Amplitude should be same.

[01:08:09]1 2 3 4 right now you can what you do to the frequency now frequency should be less right frequency should be less frequency is less wavegen how I should draw frequency less wavelength now the wave should be longer than the previous on agree >> now the wave should be longer than the previous one >> before eight boxes is one wave no so now I'm going to take 10 box for one wave make sense before eight box was one wave now the wavelength is more frequency less think about wavelength wavelength when you when you when you draw for wavelength automatically frequency will come so Before eight box was the wavelength now wavelength should be more why x-rays wavelength is more eight boxes wavelength before now now I'm going to take 10 box for the wavelength before this red dot is the wavelength now I'm going to take 10 boxes so more than the previous one but you have to maintain you have to maintain the amplitude same top and bottom same be very carefully draw That honey structure.

[01:10:04]One, two, three, four.

[01:10:10]One, two, three, four, and five. One, two, three, four, and five.

[01:10:22]One, two, three, four.

[01:10:44]Five. 1 2 3 4 5.

[01:10:48]1 2 3 4 5 3 4 5. Right. 1 2 3 4 5. 1 2 3 4 5. 2 3 4 5 2 3 4 5 1 2 3 4 Okay.

[01:11:29]H that way you draw amplitude should be four wavelength before 8 this dot was the previous wavelength now I have increased the wavelength to 10 before dot was the wavelength now I increased the wavelength to 10 you don't need to worry you will be drawing in a separate paper but this is actually a structured question When you're doing it in the structure disable properly do that is that Roman four of the six waves given in the electromagnetary spectrum above which has the highest frequency Tell me which one has the highest frequency.

[01:12:25]>> M >> Roman five. A diagram depicting two instances P and Q of an activity done in the lab to study a certain characteristic of sound wave is given below. Keeping a ruler in a table vibrating it. What you actually checking here?

[01:12:43]You are testing the frequency. You're testing the frequency. How are you testing the frequency? When the length of the ruler is less, frequency is high.

[01:12:55]When the length of the ruler is high, frequency low. Opposite condition. When you decrease the length, frequency increases, vibrations are more. When you increase the length, frequency decreases, vibrations are less.

[01:13:11]A hex blade is kept on a table and a heavy metal block is kept on the blade.

[01:13:15]When this activity was done as shown in the figure then the blade was vibrated.

[01:13:19]Which characteristic of sound wave can be studied from this activity? Ah they're checking the frequency from frequency. What characteristic in the sound you study?

[01:13:30]Uh we study pitch characteristic is pitch.

[01:13:35]Ba on which physical quantity does the characteristic you mention about depends? Pitch depends on what?

[01:13:41]>> Frequency.

[01:13:43]>> Frequency. What conclusion can be arrived at through this activity?

[01:13:49]When the length decreases, frequency increases. Or you can tell when the length increases, frequency decreases.

[01:13:57]So write it there.

[01:13:59]When the length decreases.

[01:14:07]When the length decreases.

[01:14:17]When the length decreases, frequency of the wave increases.

[01:14:31]Frequency of the wave increases.

[01:15:03]Oh, sorry.

[01:15:51]See what what conclusion can be arrived at through this activity that's what I told when the length decreases frequency increases.

[01:16:02]Roman six. How does the speed of sound in air vary with the temperature? And tell me how does the speed vary with the temperature?

[01:16:10]When the temperature increase speed of sound in air will >> increase as well as you can tell when the temperature decrease speed of sound will increase.

[01:16:25]>> You can write that when temperature increases speed of sound increases. When temperature decrease the speed of sound decreases that's 2016 this is actually a provincial paper northwestern province paper the following image shows a sound wave associated with sound created due to collision of metal ball.

[01:16:53]Write the wavelength and the amplitude respectively by using English letters in the image.

[01:17:02]Uh now what is the wavelength?

[01:17:07]Wavelength. Tell me the English letter.

[01:17:09]Any two English letter you use?

[01:17:13]A >> AC can be >> or you can tell B >> PD write AC and what else they asking? Amplitude.

[01:17:28]Amplitude. What is that?

[01:17:32]>> A K E. Even you can tell a >> if >> a e also you can tell or you can tell a s.

[01:17:42]See that you all probably write it wave separately amplitude separately.

[01:17:46]Question B. What is the frequency of the wave?

[01:17:51]Now they are telling this wave is occurring for 1 second.

[01:17:57]In 1 second how many waves are there?

[01:18:00]Take a count. This is one wave. No, I'm asking how many waves this full is one wave.

[01:18:09]>> And this is another wave. How many waves are there?

[01:18:12]>> Two waves.

[01:18:13]>> Two waves in how many second?

[01:18:17]>> 1 second.

[01:18:17]>> 1 second. Two waves in 1 second. What's the frequency?

[01:18:22]>> 1 / two. H two waves in 1 second. What's the frequency? Two hertz.

[01:18:32]Two waves are happening in 1 second. Can two herz is the frequency. Look at the definition for frequency. What's the definition I give for frequency? What is frequency? What is frequency?

[01:18:48]>> Number of waves in 1 second. So they are telling in 1 second there are two waves.

[01:18:56]For this two 1 second is going in 1 second. There is two waves. Now how many waves are there in 1 second?

[01:19:06]>> Two waves are there. Then frequency is two.

[01:19:11]Right? If it is hard for you just have this equation to calculate frequency.

[01:19:16]This equation is not there in your levels but you can use this. You can calculate frequency by number of waves divided by time. That way you can calcate frequency. But tell me how many waves are here?

[01:19:35]How many waves are here?

[01:19:37]>> Two.

[01:19:37]>> Two.

[01:19:37]>> Two waves. How much of time is taken for that?

[01:19:41]>> 1 second.

[01:19:42]>> 1 second.

[01:19:43]>> 2 / 1 is how much?

[01:19:46]>> Two.

[01:19:47]>> Two.

[01:19:48]>> Two hertz. If you want you use this equation, write it together with the equation page and key. You can use this if you want the calls I have come.

[01:20:07]Hello Krisha.

[01:20:11]Yeah. What's the result?

[01:20:14]Very good. Very good. Very good. Keep working.

[01:20:17]Yeah. I I'll call you. I What?

[01:20:27]Very good. Science is That's it. That's it. I'll meet you all.

[01:20:32]I'll meet you all next time.

[01:20:35]Okay. I'm at a class.

[01:20:39]Okay.

[01:20:46]Nothing today.

[01:20:48]Frequency number of waves divided by time you can use that number of waves here two waves time taken once again two herz see what find the velocity of the wave if the distance between a and b is.5 m on distance between a is.5 m on a distance is.5 m it seems I'll redraw it separately AB distance is.5 m. It seems AB distance is.5. This is A. This is B.

[01:21:27]This is C. AB distance. This distance AB distance is.5 m. Now tell me what is the wavelength there?

[01:21:40]>> 1 m.

[01:21:41]>> Ah wavelength is 1 m.

[01:21:45]AB distance is 0.5. Now wavelength wavelength AC is the wavelength.

[01:21:50]Wavelength is 1 m. Hurry I know the wavelength. What else I know? They are telling find the velocity of the distance in between AB is 0.5 m. Right?

[01:22:00]This distance is 0.5 m. And we know full time taken is 1 second. That also we know full time taken here is 1 second.

[01:22:08]For this full time is 1 second. Tell me full time is 1 second.

[01:22:14]For this part of the wave, how many seconds are gone?

[01:22:22]>> If you want, you can use it. Otherwise, you don't need to, you don't need it as well. So, however, wavelength you know it is 1 m. Time you know it is 1 second. Time you know it is 1 second. Wavelength 1 m time 1 second. They are asking the speed of wave. Tell me what's the equation for speed of wave fd >> wavelength I know wavelength 1 m I know what's the frequency >> 2 I know 1 second full time I know 1 second tell me for one single wave for one single wave one single wave what's The time >> second tell me that as fraction more easy >> 2 second 1 / 2 second is for one wave that is what time I told the name for that one wave time taken is what time >> period >> periodic time that is the period so I know period is half a second if I know period is half a second can't I find the frequency Yeah. Okay.

[01:23:44]>> So you find the frequency. How to find the frequency? Frequal >> period. Period. I know half.

[01:23:53]Now do the math then tell me what's the frequency?

[01:23:58]>> 2. Tell me what's the frequency.

[01:24:00]>> 1 / 1 / two. Division under division.

[01:24:04]Division under division becomes what?

[01:24:10]1 / 1 / so division and division becomes what >> multip 1 / two I can take it on top that is 2 herz that's next division and division is multiplication so two I take it on top it's two hertz so frequency I know two hertz frequency 2 herz wavegen 1 m tell me what's the what's the velocity. What's the speed? 2 into 1 is 2. Speed comes in m/s. 2 m/ second.

[01:24:45]Got it.

[01:24:55]So see for two waves I know 1 second.

[01:24:58]Then one wave it is half a second.

[01:25:00]That's a period reciprocal is a frequency. So 1 / 1 /2 is 2 Hz. Frequency is 2 Hz. Wavelength is 1 m 2 into 1 2 2 m/ >> can't we use the frequency found in the part B in a yes we found it you can use it here you have you can use You can use this and do it again. No need to fine. Roman five. What is the device that can be used to demonstrate transverse and longitude waves in the lab? Tell me what's the device I use.

[01:25:49]What's the name?

[01:25:51]What is this called?

[01:25:59]>> Romans 6. Write to characteristics of light wave which can be taken to defer it from above wave created through this activity. Right to characteristics of light waves light waves which can be taken to defer it from above wave created through the activity. Now this is what wave this is sound wave. Sound wave is what type of wave? Mechanical wave.

[01:26:26]>> This is light wave. Light wave is what type of wave? Electromagnetic >> electromagnetic wave. Tell me two difference between electromagnetic wave and mechanical wave medium to propagate. Mechanical wave need a medium to propagate.

[01:26:44]Electromagnetic wave do not need a medium to propagate. Neither mechanical waves need a require a medium propagate. Electromagnetic wave do not need a medium propagate. one point number two electromagnetic wave has two waves oscillating together electrical and magnetic wave mechanical wave doesn't have such a property those are the differences you can so right now mechanical wave mechanical wave requires a medium to propagate requires a medium to propagate.

[01:27:36]Requires a medium to propagate an electromagnetic wave.

[01:27:53]An electromagnetic wave do not need a medium.

[01:28:07]Do not need a medium.

[01:28:16]Next. Right.

[01:28:21]Electromagnetic wave.

[01:28:25]Electromagnetic wave has electrical and magnetic wave together.

[01:28:35]Electromagnetic wave has electrical and magnetic wave together.

[01:28:45]And mechanical wave is a individual wave.

[01:28:50]Mechanical wave is individual Mechanical W individual.

[01:29:02]Right. Last question. This 2023 Royal College paper.

[01:29:08]In our day-to-day life, we use mobile phone for the communication. It uses electromagnetic waves. Write two characteristics of electromagnetic wave.

[01:29:16]Again, characteristics of electromagnetic characteristics of electromagnetic wave.

[01:29:21]All right. I told >> do not require medium to propagate.

[01:29:32]Now electromagnetic wave they have electric and magnetic wave.

[01:29:37]Is that electric wave and magnetic wave affected by external electric and magnetic wave?

[01:29:44]>> No.

[01:29:44]>> No.

[01:29:46]>> No.

[01:29:46]>> That's a characteristic. So electromagnetic wave has electric and magnetic wave. It is not affected by external electric and magnetic field.

[01:29:55]Right? What can you tell about the speed of electromagnetic wave? There's a constant speed for electromagnetic wave in vacuum. What's the speed of magnetic wave in vacuum?

[01:30:04]13 >> 3 into 10 ^ >> write down the characteristic.

[01:30:15]Electromagnetic waves do not require a medium.

[01:30:22]Electromagnetic wave do not require a medium.

[01:30:33]Number two, it is not affected by It is not affected by It is not affected by external electric and magnetic waves.

[01:30:57]It is not affected by external electric and magnetic wave.

[01:31:18]And you can write speed of electromagnetic wave in vacuum is speed of electromagnetic wave in vacuum is 3 into 10 8 m/ into 10^ 8 m/2.

[01:31:40]What is the type of electro wave used in mobile phones? Mobile phones uses what?

[01:31:48]>> Microwave.

[01:31:50]>> Roman three state a difference between mechanical wave and electromagnetic wave. Already I told what's the difference between mechanical wave and wave. Mechanical wave do not require a medium. Electromagnetic wave. Uh sorry mechanical wave require a medium.

[01:32:04]Electromagnetic wave do not require medium.

[01:32:09]>> We can write mechanical wave do not require medium. Mechanical wave require a medium require a medium.

[01:32:16]Electromagnetic wave do not require a medium. That we already wrote as mechanical require a medium electromagnetic wave do not require medium.

[01:32:28]Last question.

[01:32:31]Again calculation velocity of electromagnetic wave in 3 into 10 m/s.

[01:32:39]If the wavelength is 300 - 11 m, calculate the frequency. I have the speed, the velocity, I have the wavelength, they're asking frequency.

[01:32:51]I have the speed 3 into 10 ^ 8 m/s.

[01:32:57]I have the wavelength. How much was the wavelength?

[01:33:02]3 into 10^ - 11 - 11 asking frequency.

[01:33:13]How do I get out? What's the equation?

[01:33:19]V= >> F lambda >> F lambda.

[01:33:24]Now you have to play with the the the factors there. V is given, lambda is given. They asking frequency.

[01:33:33]So if you want to find frequency, you have to subject frequency. If you subject frequency, lambda goes to the other side. Go tell me multiplication on other side become >> division.

[01:33:44]>> Deviation. So F is equal to velocity divided by the wavelength.

[01:33:51]Velocity is how much? 3 into 10 ^ 8 m/s.

[01:33:58]Wavelength is how much? 3 into 10 ^ -1 m on the math.

[01:34:16]Do it.

[01:34:19]What will happen? 3 and 3 will cancel.

[01:34:24]How do you work with 10^ 8 / 10 - 11?

[01:34:26]How do you work it out?

[01:34:29]10us 11 I can take it on top can take it off I take it on top 10 ^ - 11 become what >> 10 ^ 11 >> uh 10 ^ + 11 m and m will cancel off you will have s the power minus one har frequency comes in sus one I told you another unit for frequency now do the math what's the answer 10 the^ Power >> 19 sus one is hertz. If you want you leave the answer like this or you can write 1 into 10^ 9 just 10^ 19 hertz or 1 19 both frequency frequency Okay, that's it. No. Did I leave anything?

[01:35:44]No.

[01:35:48]My waves is done. I told I'll give update. I forgot that update. Um update is this next Thursday. The coming Thursday. Today is Friday. Next Thursday. uh we are doing this kind of a discussion on optics lesson geometrical optics that lesson as right so today now waves is done uh next is optics discussion okay enough for today then time will be 9:30 9:30 Okay. Uh just be in the groups and the channel. So I'll put the updates right now. Now this one I didn't even inform in the theory classes. No. Suddenly you'll get updates like that. So see that all of you be in the channel and the WhatsApp group. So you know how the process is working.

[01:36:42]Sometimes I won't tell in the theory class. I forget in the theory class but we are doing it in the online session.

[01:36:48]Right. Enough for today. I'll post the optics lesson to you as well. Get ready with the optics lesson. Next week we'll do the optics.

[01:36:58]Why? Why on Thursday? Actually the plan is this. Optics is a big lesson. In case if there's anything left in Thursday, so I can finish it at least on Friday. I have planned it for Thursday in case if anything gets left there, I can take Friday also and finish it. But if I schedule it on Friday, it's hard for me.

[01:37:17]After that, the upcoming weeks are very busy for me. Okay. Okay. Then enough then keep working hard. Next is your results.

[01:37:25]must now start working final 6 months.

[01:37:28]Bye. Good night.