So this is the information associated a to this train okay very much important ladies and gentlemen that you write down all this information so remember guys frequency is measured in heads okay so for some reason if you see a value or any magnitude and you see Hz before you can even read the whole statement you should be aware that there's a value of magnitude for frequency. Okay so you'll be reading the statement with the aim of trying to figure out for which frequency is that magnitude okay so ladies and gentlemen before I go deep into you know dishing out information.
Please ladies and gentlemen do allow me to say it's very much important that I say it's very much important because ladies and gentlemen what I'm about to say is massively important okay guys a day without learning something new it's a day wasted. Okay so please do make sure that by the end of each and every question or by the end of this question ladies and gentlemen make sure that you learn something new okay so guys as we continue I just wanted to indicate that we've actually got the most important information in relation to that train. Okay so it's a speed which is a constant speed of 20 meters per second we've got the frequency which is emitted by the whistle as the train is approaching either the station or the listener okay ladies and gentlemen frequencies measured in heads speed or velocity in meters per second
very much important ladies and gentlemen so guys an observer so this is actually an observer okay an observer standing on the platform which platform this platform ladies and gentlemen which is a the platform on the station. Okay so this observer who is standing on the platform hears a change in pitch ladies and gentlemen as the train approaches him passes him and moves away from him okay. So guys remember it doesn't necessarily mean this train is only coming from that direction moving in that direction very much important ladies and gentlemen I only decided to draw that to draw it that way okay so anyone could draw it in the opposite way such that the train is moving from that direction moving in that direction.
Very much important ladies and gentlemen that you take into consideration that the direction in which the train is moving in this case it's not really a real deal okay so ladies and gentlemen I just want to quickly indicate to you that you've got let's say this is a stage one of phase one stage two of phase two stage three of phase three okay so guys we've got the first stage which is where a you know the train approaches an observer okay so here the train is actually approaching an observer okay very much important ladies and gentlemen. Obviously as this train is approaching the observer ladies and gentlemen they've just indicated that he hears a change in pitch okay so obviously you're having compressed wavelengths as this train is approaching him okay
so that means uh the noise of the whistle is actually increasing this is practical ladies and gentlemen you know if a car which is you know the driver let's say is the driver playing a music you know sorry you know very well ladies and gentlemen that as the car approaches you know the sound of that music is actually increasing and as it actually passes wherever you're standing ladies and gentlemen. At that point that's where the frequency registered by the listener versus the frequency emitted by the source are the same okay so ladies and gentlemen that means the amount emitted by that source and by the amount registered by the detector or an observer who's listening is the same there's no change in pitch there's no change in wavelength okay so it's more like you are the same as someone who's actually in that particular source okay but the moment ladies and gentlemen but the moment that particular source moves away which is at this stage where it's actually moving away from an observer that's where the wavelengths are now increasing ladies and gentlemen
the wavelengths are increasing. What does it mean so it means the
sound is now decreasing okay so ladies and gentlemen I‘ve just indicated that I'm
going to prepare a complete lesson where I cover all the necessary information
that you need to know about before you start with the previous questions and
most importantly just before you start with your exams ladies and gentlemen because
I assume by the end of each and every lesson that I conduct you go to my
telegram channel to go through the question papers that I've posted assumingly
you do treat those questions. Okay so guys I think I've tried to actually
explain all the relevant information required for us to be able to tackle these
questions okay so some of the information we might discover as we continue with
the questions very much important ladies and gentlemen that you fully
understand what is given on the statement.
Okay so guys remember I've just indicated that the
information that I provide doesn't necessarily mean that I've actually provided
all the necessary information and anything else that I haven't mentioned might
not be important okay so i know some of you ladies and gentlemen some of you
who have done what I was taking long to explain a you've actually noted down
the velocity of the observer or the velocity of the listener very much
important ladies and gentlemen the moment they give you the speed or the
velocity of the source or the moving train ladies and gentlemen at the same
time you ask yourself what happens to the listener what happens to the observer
what happens to a you know the detector as far as speed is concerned ladies and
gentlemen they've just set a train it's approaching a station at a constant
speed with its whistle blowing at that frequency and observer ladies and
gentlemen standing on the platform very much important ladies and gentlemen the
observer is standing on the platform.
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