Importance of correct substitution


But in a different scenario can you see in this case they say this is a specification ladies and gentlemen they say while the train is approaching him so that means you might also be requested to calculate let's say for example the frequency as the object is moving away from him or from an observer. okay very much important ladies and gentlemen that you take into account how the question is asked very much important ladies and gentlemen that you take into account what the question wants you to do okay 

so they wouldn't give you a mark ladies and gentlemen if you do calculations while your calculations are actually referring for the train while moving away because you are not following instructions given within the question ladies and gentlemen please do make sure that although the substitution might be the same. But as a marker in the making center if I'm working on your paper, ladies and gentlemen or your answer sheet you give me an impression that even on the upcoming questions you do apply your mind it's not like you just borrowed, substitution or a question from your friend next door. 

Very much important ladies and gentlemen please give me an impression that you fully understand what you're dealing with okay so by having your answer in order it also gives me the confidence to pay full attention into your answer sheet even if you don't ladies and gentlemen our work is to try and look for way we you know we can give you some marks when you deserve to get those marks.

Okay we don't just give you marks we give you marks based on how you answer the questions okay so ladies and gentlemen for the last time I will just read the question which says calculate the frequency of the sound that the observer hears while the train is approaching him use the speed of sound in air as 340 meters per second okay so we've got a the speed of a let me just say the speed of a this is the same as v ladies and gentlemen 

on that formula which is 340 meters per second okay very much important ladies and gentlemen so I always tell my learners that this chapter is not really difficult ladies and gentlemen uh you know you only score maximum max if you fully understand the scenario there's no need for the examiner to give you a diagram you can visualize from the given statement okay that's what I'm trying to do when I draw that diagram that when you're given a statement similar to this one if you're quick enough ladies and gentlemen do not just try to have everything in your mind okay 

just try to quickly draw all the information that you can write all the information that you can be able to write and then from there based on the questions and the manner in which questions are asked and most importantly the order in which questions are asked they are going to guide you in terms of what to do as your first step in answering the question okay so ladies and gentlemen in this case this is 6.2. So in this case ladies and gentlemen this is the formula that we'll be using just wrote it there so that you know we obviously all of us know that formula is given.

Also on your formula sheet let me just quickly check exactly where is that formula because I know ladies and gentlemen some of you don't even a you know take the effort to have a look at this a formula sheet when you treat previous question paper some of you just straight away answer the questions and only way to use this thing in a in exam please ladies and gentlemen try to familiarize yourself with the formula sheet and not only the formula sheet but also the physical constants ladies and gentlemen very much important that you familiarize yourself with all of this information okay so guys um let's check there we've got equations of motion here is force here it's work energy and power here we've got wave sound and light here we've got electrostatic circuits. 

No let me see it's electrostatic here we've got electric circuits we've got alternating currents um so our formula should be somewhere there okay waves sound and light we use this formula. Ladies and gentlemen they just give you all the formulas related to that chapter based on the question that you're dealing with. You have to choose which one is the relevant formula to use okay so here's the formula ladies and gentlemen. This is the formula that we'll be using for this question okay so guys a I've already written down that formula over there you can see let me just quickly go back to that question where is that question ladies and gentlemen this is our question six. This is where we are so remember ladies and gentlemen if you're not able to see exactly what's written there I'm sure on your mobile at the top right corner there are three dots if you can just click there on those three doors you can also click on quality then down there they should be advanced then you can just click on a I think it's 480 or 300 and something p then as soon as you click there then the quality is going to adjust itself and you'll be able to read everything that is on the screen. 

And again ladies and gentlemen this question paper should be posted on my telegram channel but I assume a you are able to clearly see everything on the screen so ladies and gentlemen let's now start with a question for i mean 6.2 okay so obviously this is the formula that will be using there is v this is plus or minus a we've got v l over there over this is v plus or minus v s multiplied by fs okay. Very much important ladies and gentlemen that you fully understand this formula okay so in terms of the plus or minus the plus or minus obviously ladies and gentlemen this depends on the velocity of the listener relative to the velocity of the source okay so that means that plus or minus is not really for that v it's not really for that v that v it actually refers to the speed of velocity of the a okay so obviously then we are not interested in the direction of um the velocity of the air okay so the plus or minus it's based on the velocity of the listener of the velocity of an observer relative to the velocity of the source very much important ladies and gentlemen.

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