Since A/L examination is starting in few days I thought of writing a quick post about something related to A/Ls. I will be explaining Doppler Effect and how to do calculations using formulas easily. This was taught to me by my Physics teacher in school who also happened to be my class teacher. Literally she is the best Physics teacher I had in my life and I didn't even need tuition classes for Physics. (She insisted me on practicing more problems so I went to a Physics class where the teacher focused more on questions than theory.) But I learned all the theories and how to apply them from her. So today I'm gonna share with you one of her lessons. It will get you full marks on your Doppler effect question in paper.
So lets get started by What is Doppler effect. Doppler effect is the phenomenon of observed changes in the frequency of energy wave transmission when relative motion occurs between the source of wave transmission and the observer. In simple words, it is the observation of frequency change when there's a relative motion between the observer and the source of energy transmission (In A/L syllabus usually sound is used.) In practical life you may feel a honking cars sound increases as it comes towards you and decrease when its going away from you. This happens because of the Doppler effect.
So the general formula for this is,
Observed Frequency =(Velocity of waves relative to the observer/Velocity of waves relative to the source) x Actual Frequency
Most people get confused with all the velocities and where to plug in all those values. And my teacher taught me a trick for it.
If the velocities are in the opposite directions always add them. If they are in the same direction subtract them.
Now let me explain what she said with an example.
Assume we have a moving source with a frequency f0 and source velocity is "s" while velocity of sound is "v" and the observer is stationary.
Lets first see what are the velocities that are relavant to the observer. Since there is no observer motion we only have the velocity of sound in air "v" for the velocity of waves relative to the observer.
The source is moving and also it emits waves in the same direction it's moving. So they should be subtracted according to the convention we agreed. So it is " v-s" . Now when we plug it into the equation we get as follows.
Observed frequency (f) = (v÷(v-s)) f0
Lets consider another scenario where source is moving away from the observer.
Again velocity relative to the observer is only v because observer is stationary, but source has two velocities. This time v and s are opposite in direction to each other. So we add them together.
Observed frequency (f) = (v÷(v+s)) f0
Now lets consider a scenario where the observer (at a velocity of o) and source are moving towards each other.
Since the observer is also moving now we have to consider both v and o when it comes to velocities relative to the observer. v and o are in opposite directions to each other. Therefore we add them together. (v+o)
When it comes to the source we have two velocities in the same direction. Therefore we subtract them. (v-s)
Now the final equation looks like this.
Observed frequency (f) = [(v+o)÷(v-s)] f0
Scenario 04 : Observer moving away from a moving source
Now the velocities related to observer, v and o are in the same direction. therefore we subtract them. Velocities related to source are also in the same direction as in the previous example. so we subtract them too.
Observed frequency (f) = [(v-o)÷(v-s)] f0
So that's it for today guys. Hope this helps you and comment down below if you need me to cover any more topics. I will try to cover them up once I'm done with my exams. Thank you for reading my blog!
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Photo-credits
Photo-credits
Doppler image : Flickr
Calculation images were made by me
This is so helpful thank you so much ma'am I really enjoyed most of your answers and it really motivated thank you so much again for those tips on how to face the chemistry paper strategically those golden advise I will never have got from anyone if I didn't come across your blog. Please keep writing more on A/Ls and I hope you write an answer on how to approach organic , I am self studying it because my teacher is kind of slow although he's amazing. May God bless you more and more and all the best for your future. I owe you a lot for these advises.
ReplyDeleteHi, Thank you so much and I'm happy if my articles helped you. I will write a post about organic chemistry as soon as I finish my final exams. If you have anymore ideas about topics I should cover feel free to let me know. :)
Delete*it really motivated me
ReplyDelete