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“America has looted black people. America looted the Native Americans when they first came here, looting is what you do. We learned it from you. We learned violence from you. If you want us to do better, then damnit, you do better.” —Tamika Mallory, Nat. Co-Chair of Women’s March

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do you guys realize that…the videos and articles about the “good cops” who are “protesting” are propaganda designed to make you think “not all cops are bad”? do you realize that when the chief of police of flint said “let’s not make this a protest, let’s make it a parade,” he was successfully de-escalating the situation and dissolving the protest?

the police force has been corrupt since long before you and i were born. people don’t become cops to protect and serve, they become cops to feel strong and to use their strength against others. you are falling for propaganda if you believe that white men kneeling a la colin kaepernick mean the cops you see firing rubber bullets and batoning people are the exception to the rule. 

all cops are bastards. full stop. 

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How is the Doppler Effect Used outside of the Physics Classroom?

TOPIC 9.5

like in maths, students raise a lot of questions regarding the actual, real world use of what they learned in class. in a lot of situations, i would agree with those points raised, such as when looking at quadratics and trigonometry in maths- when am i ever going to need that in my future? 

however, the doppler effect actually does have a use outside the classroom, especially for those who desire to go into air traffic control or law enforcement, the latter which i heavily discourage. the doppler effect is used by air traffic controllers to determine the speed of a plane in flight from the ground, and cops use it to measure the speed of passing cars. 

how does this work exactly, though? well, let’s use an example that concerns the medical world. in hospitals worldwide, staff use ultrasound machines in order to retrieve required imaging of whichever patient they need. this, in principle, is using the doppler effect. for example, when checking the blood flow within an artery, a device called a transducer is planted on the skin where the artery would be under. from there, the transducer releases pulses of ultrasonic waves which then proceed to bounce off the blood cells at different frequencies due to the doppler effect. 

a more obvious use of the doppler effect in the medicinal world is in the ultrasounds used during pregnancy. when pregnant, people are asked to regularly check in with their doctor in order to track the baby’s progress. to do this, they utilise an ultrasound machine, which uses the doppler effect in a similar way to the aforementioned transducer.

okay yeah so this was a lot longer than i thought- go take a break after reading this! maybe take some time to look around the blog and read up on some things. if not, maybe go get some water, get a bite to eat, or just relax for a few minutes. take care of your body- studying can wait. don’t hurt yourself over a few extra minutes of studying.

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LAST DOPPLER EFFECT EXAMPLE

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DOPPLER EFFECT EXAMPLE QUESTION

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EXPLANATION OF THE 9.5 EQUATIONS 

here are the screenshots of what my teacher had said about this in our lesson!

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DATA BOOKLET (9.5)

9 . 5 :   T H E    D O P P L E R   E F F E C T

here, you’ll find all equations necessary for topic 9.5 from the data booklet!

K E Y

f’ = perceived frequency

f = actual frequency

v = wave speed

us = velocity of the source

uo = velocity of the observer

λ = wavelength

Doppler Effect for Light (last equation)

v = relative speed of observer and source

c = speed of light

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PRACTICE WITH CONSTRUCTIVE/DECONSTRUCTIVE INTERFERENCE FORMULAE (9.3)

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Example Questions for Thin Film Interference (9.3)

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DERIVATION OF THE THIN FILM INTERFERENCE EQUATION (9.3)

note: this is from my teacher’s slides! this explained it better than i could ever articulate 😭familiarise yourself with this derivation and the equations involved, as future teachers could look to test you on your knowledge of thin film interference and try to confuse you by asking you something regarding this derivation!

if you have any questions regarding this, don’t forget you can shoot me an ask, a private message, or even find me at one of my given social media accounts.

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Thin Film Interference (9.3)

it’s time for the next topic of 9.3-- thin film interference! 

first things first: what is thin film interference?

thin film interference once again has to deal with constructive and destructive interference. it’s because of these forms of interference that when a light shines on a soap bubble, one can see a rainbow or a pattern of colours. 

before we get into why this happens, let’s understand one thing: what happens when rays cross into a different medium. there are two gifs to show you what happens in a simple way:

in this gif, you can see a wave from a certain density medium travel and cross into a medium that is denser than its own. whenever hitting a medium, a part of the wave will continue while another will reflect. when a wave travelling in a less dense medium travels into a denser medium, the reflected wave will be in inverse, or will observe a 180 degree inversion.

however, when a wave in a denser medium travels into a less dense medium, the reflected wave will simply return- there will be no inversion.

now that this is known, we can begin talking about thin film interference itself. we know that when a wave from a medium reflects off a denser medium, the reflected wave will inverse and observe a 180 degree phase change. where did we mention 180 degrees phase change before? oh, yes, in destructive waves- thin film interference is also based upon these waves. ultimately, this interference deals with reflection upon boundaries of mediums, and the density of those boundaries of “film” will help determine if the waves reflected will undergo constructive or destructive interference. observe this soap bubble:

in this soap bubble, which is in the air, there are areas where there seems to be colours shown, which indicates the presence of constructive interference. however, when looking dead straight at the bubble, there are also patches of no colour reflected, which indicates the presence of destructive interference. why is there destructive interference? simple. let’s look at how the rays of light travelling through this simple look drawn out:

in this image, we can see what happens to an incident ray when it travels through a soap bubble. it starts in the air, which let’s say has a density of 1.0. it then travels into the soap film, which is denser- let’s say 1.3. this means that the reflected ray of the incident ray will undergo a 180 degree phase change. let’s look now at pink ray next to the initial reflected ray. this ray would undergo no more phase changes, as soap film is denser than air. so, when it reflects on the boundary of air, the reflection will stay as is. thus, when it exits, it will undergo destructive interference with the incident ray’s reflection, as they are exactly 180 degrees out of phase. thus, the colour will be dulled or even nullified.

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Practice with Me then Do It Yourself!

the answer to 25c can be found in the answers page!

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Young’s Double Slit Experiment

a great video explaining and detailing thomas young’s “double slit experiment” that helped prove that light was, in fact, a wave. very informative and very entertaining, too.

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9.3 Example Question

see how to use the double-slit diffraction equation in a word problem!

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Double-Slit Diffraction vs Single-Slit Diffraction

link to video mentioned

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Interference (9.3) [Review]

W H A T   I S   I T ?

quick review of the last lesson! 

interference, quickly defined, is a phenomenon in physics that happens when two waves meet each other whilst traveling in the same space and same medium. 

there are two types of interference: constructive and destructive. if you forgot what these terms meant, check out this vocab post from earlier!

it is this interference that then creates diffraction patterns, whether that be in a single-slit diffraction, which was last topic (9.2), or in any diffraction that occurs through two or more slits, which will be discussed in this topic, 9.3.

see an example of interference below the cut! (as well as a review on superposition!)

this is a perfect visual representation of interference. why is this occurring? let this serve as your last review of superposition for the remainder of these lessons.

S U P E R P O S I T I O N

superposition is the theory/principle that serves as a basis for this topic. the theory simply states that if two waves were to overlap and/or interact, the two waves would then combine. 

if the two identical waves are 180 degrees or π radians out of phase, as seen in the left-side column, the waves will superimpose, and because the troughs and crests stack atop each other, the wave will completely cancel out.

 if the two identical waves are perfectly in phase, the amplitude will double, as troughs stack atop troughs and crests stack atop crests.

 if the two identical waves are out of phase but aren’t 180 degrees out of phase, superposition will still occur, and the resultant superimposed wave will be how the two original waves added onto each other would look like. 

what would these wave look like, superimposed, when they meet?

watch this video to check your answer!

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quick announcement.

this blog is, yes, a physics blog. that is true. however, that does not make it any less of a blog. this is tumblr, a site that i have been on since 2017. i have grown immensely on this website, and the things ive read and seen spread around have opened my eyes in so many ways that i cant even count anymore. ive grown as a person and as a global citizen, and it would be wrong of me to not try and inspire the upcoming ib students to do the same. as an ib student, you’re expected to be a good global citizen, to be a good person, to be a good human being- not just a good student. in between these lessons i’lll keep reblogging a few eye opening posts that can serve as “rest reads.” while you’re taking a break from the physics, take the time to read up and educate yourself on the global situation. don’t go silent- let your voice be heard. speak up. use the privilege you have for good. 

as an ib student, you've been able to live a life with education. you've been able to be educated, been able to reap the benefits of education. use that privilege, don't let it rot in silence. do your research, form your own stance, speak out against injustice. use the tools your teachers and schools have instilled in you and use it not to keep yourself ignorant and indifferent from the global climate- no, use it to help in whichever way you can and become an advocate for a free world, an advocate for a world where we can all live in peace and comfort in our own skin.(edited)[3:26 AM]

don’t breed hatred in you, breed love. breed love for humanity, love for this world, love for one another as equals. help fight for this love to stay, for a world where oppression can no longer take us by the throats and silence us. we must be better, and to be better we must learn. we must change. we must educate. we must start. and you can start here.