[The Fifteenth Blog] Quantum Physics.

I realize that I made a ridiculously stupid mistake on the physics test today. Rah. How frustrating. >_< And more sad news (or not, haha): this will be my last physics blog post. Aww... :[

     I don’t really know how to relate quantum physics to everyday life, though, except by likening the photoelectric effect to photosynthesis, which is quite important in our lives, I'd say (biology and physics in one post?!? o_O). And of course I don't really know anything about photosynthesis anymore because I don’t even remember what I (should have) learned yesterday, let alone information from 9^th grade biology. So let’s get cracking.

     The photoelectric effect is the ejection of electrons due to light striking a material. An increase in light intensity results in more electrons being released because more intense light => more photons => more electrons emitted. However, the light must be greater than a certain frequency, otherwise no electrons will be emitted at all, regardless of the intensity, since low frequency => less energetic photons => not enough energy to free electrons. An equation we can relate to the photoelectric effect is E = KE + ø, where E is the energy of the photon (also equal to hf), KE is the kinetic energy of the released electrons (0.5mv²), and ø is the work function of the material (the minimum amount of energy needed for an electron to be ejected from it). 

     Photosynthesis is like the photoelectric effect because in both cases, light striking a material results in the emission of electrons. When sunlight shines on a plant, chlorophyll molecules absorb it and they become excited, releasing electrons. (Some complicated processes occur here to transport electrons...).  And by the end, the electrons have been converted to ATP, and photosynthesis has successfully converted light into sugar. :]

[The (Late...) Fourteenth Blog] Light Interference.

[Bubble Pop by Hyuna]
An appropriate song, given the topic of this blog post. I don't actually like this song, but I had to. Hehe.

And to start this off, I apologize for this blog being so late. >_< [Hopefully it won't happen again.]

Now for the actual post:

Here we have a lovely picture of a gigantic bubble. [And an excited (or frightened...) child standing there on the side. Haha.] My friends took it when they went to the Children's Discovery Center way back when in...eighth grade.


As you can see, not only is the bubble enormous, but it is also adorned with pretty, shiny colors. Now, prior to being in physics class, I would see the colors and be captivated by them but not give them a second thought. I had no reason to know why they were there or how I could see them - they just were and I just could. [I never have been a very curious child...] But now I am able to explain to you the physics behind the appearance of those colors [or so I hope]. 


This color-producing phenomenon is known as thin film interference. When a beam of light travels from the air to the thin layer surrounding the bubble, it is reflected off of both the outer and inner surfaces of the bubble. When light rays are transmitted through the film before being reflected off of the inner surface, they travel a farther distance than rays reflected directly off the outer surface, resulting in a difference in wavelength between the two reflected beams. These beams interfere with each other, both constructively and destructively, resulting in the display of colors that we see. If the wavelengths are in phase, then constructive interference occurs and the color of that particular wavelength is reinforced. If the wavelengths are out of phase, the opposite holds true - destructive interference occurs and the color of that wavelength is destroyed. The colors that are seen are very much dependent upon the thickness of the film, given by the equations 2nt = mλ (constructive) and 2nt = (m+1/2)λ (destructive). With thicker films, longer wavelength colors (red) are cancelled out and blue-green colors can be seen, but as the film gets thinner, the shorter blue-green wavelengths cancel and yellow hues are more prominent. Eventually the film gets to be so thin that no colors can be seen and then pop! the bubble is gone. But it makes for a pretty sight while it lasts. :]

This will be late...

       If you are seeing this before I get around to posting my actual blog, sorry that I was unable to get it done on time. Wahhh. :[

[The (Lucky?) Thirteenth Blog] Optics.

       Since it was exceptionally rainy this week (such lovely weather we had...), I was bound to see some rainbows. I live in Manoa, though, so rain and rainbows are not that big of a deal. However, as I was coming home from school on Tuesday, through the pouring rain, I saw something I've never seen before... A DOUBLE RAINBOW! [I tried to take a picture with my phone (because of course I was thinking hmm, maybe I can use this for a physics blog), but it didn't turn out so nice... Eh. Well you can sort of see the second rainbow right above the tree if you look reeeeeally hard (unless I'm just imagining things. O.O Highly likely.)]

But anyway, since my picture was not very clear, here is a better one:

       And now I will attempt to explain how this double rainbow phenomenon comes to be. Being able to see a rainbow all depends on where you are relative to rain and the sun. Rain must be going away from the sun and the sun must be shining from behind you. The formation of the rainbow itself is due to two processes: refraction and reflection. When the white light (a mixture of all colors) from the sun comes into contact with a raindrop, the light bends and breaks into its constituent colors (dispersion) based on their wavelengths. This process of light bending as it enters a new medium (air --> water) is called refraction.  Red, with the longest wavelength, refracts least, while violet, with the shortest wavelength, refracts most. The light then continues to travel in a straight line until it reaches the inside surface of the raindrop, at which point it internally reflects. After being reflected, the light refracts again when it leaves the raindrop and enters back into the air. 


       However, the array of colors that we see does not come from a single raindrop. From some we see the red, from others we see the orange, the yellow, and so forth. This is because the angle at which the light refracts  in a raindrop only allows us to see a single color from that particular one - colors refracted above would be above our eyes, and colors refracted below would be below them. Now that is how the first rainbow is...born...but what about the second? Well, the secondary rainbow is the result of two internal reflections. Instead of reflecting once then exiting the raindrop, light reflects a first time and then a second before it leaves. Because some light is lost during each reflection (since it is not totally internally reflected), the secondary rainbow appears more faint than the primary. The second reflection also reverses the order of the colors, resulting in a rainbow with violet on the outside and red on the inside. Lastly, the rainbow is curved as a semicircle because the set of raindrops that have the right angle between us, the sun, and the raindrops lies on a cone in which we, the observers, are looking from the point directed toward the sun. Of course we only see one half of it because the ground gets in the way, so that's why it looks like a semicircle. Phew. Who knew that this seemingly magical phenomenon was simply a matter of physics! :]

[The Twelfth Blog] Magnetism.

I wouldn't consider myself a very curious person, naturally, so I have probably never thought about it (although I don't think I would have noticed in the first place... :|), but after this lesson in physics, I know why so many different objects can be powered/charged by being plugged into wall outlets. It can't be that all objects require the same voltage, right? So there must be something that is able to convert the wall outlet's 120 volts into the proper voltage for each individual appliance... And this trusty tool is the AC adaptor! These are so common that many people probably don't even think about them. In fact, I'm making use of one right now, as I charge my laptop whilst writing this blog.


How it works: 
- Within the adaptor, there is a ferromagnetic core (say of iron) around which two coils (primary and secondary) are wound
- The primary coil receives the alternating current from the wall outlet, which creates an alternating magnetic flux 
- This alternating magnetic flux leads to a varying magnetic field in the iron core
- When the secondary coil is brought within the varying magnetic field, an alternating current is induced within it
- Since V₁/N₁ = V₂/N₂, V₂ is determined by the ratio of the primary coil's loops to the secondary coil's loops
- To reduce the voltage that leaves the adaptor, the secondary coil should be made of fewer loops accordingly


Well we sure do seem to learn new things every day, even things that we may never have thought about if not for physics class. :]

[The Eleventh Blog] Current Electricity.

I try not to turn on the lights in our house as often as possible, relying instead on the natural light from outside (my mother is not very approving of this, but that doesn’t stop me... :P). However, when it’s rainy and the sky is gray, or when I’m up studying in the wee hours of the night, the lights become necessary. In my room, I have a light fixture above my bed that looks like this:

[It’s kind of ironic how nice the plants look behind my window, since it has basically
been raining the entire day. Not the best weather to motivate me to do my homework. -.-]

As they are, the lights seem to be in series. However, the circuit that they are a part of is actually in parallel. Which is good, because a parallel circuit is much more efficient than a series circuit. In a series circuit, when one bulb goes out, the others go out too, because the current can no longer flow through the entire circuit. But since my lights are wired in parallel, even if one bulb goes out, current still continues to flow to the other bulbs to keep them lit. Also, the total resistance of the circuit is much lower in a parallel circuit than it would be in a series circuit, allowing more current to flow through it. In a series circuit,  R_total = R₁ + R₂ + R₃, while in parallel, 1/R_total = 1/R₁ + 1/R₂ + 1/R₃. Lastly, the bulbs will shine brighter in a parallel circuit than in series. In series, the voltage is split between the bulbs, whereas in parallel, (theoretically) all the voltage supplied by the source goes to each branch of the circuit. Since power can be defined as P = V²/R and the voltage supplied to each bulb in a parallel circuit is greater than that supplied in a series circuit, the bulbs in parallel will be brighter.

[The Tenth Blog] Electrostatic.

Today I went to a first birthday party for my mother's co-worker's daughter. Her name is Leura (after the city in Australia) and she's really cute. :] But anyway, since it was a birthday party, there were lots of balloons, which of course reminded me of...physics!

Objects can become charged by friction if they are rubbed together. I would not have done this at the party (sorry, not even for physics) because I would have looked ridiculous as well as made my hair all frizzy and such, so I'll just speak theoretically. If I had rubbed the balloon against my hair, both my hair and a balloon would have become charged. Since the rubber balloon has a greater electron affinity (Yay for chemistry. :P) than hair, it would pull electrons away from my hair (It is always the electrons that move! :]), making the balloon negatively charged and my hair positively charged.  Also, since charge is conserved, the net charge would be constant throughout the process. The balloon and my hair were both neutral at the beginning, and since electrons are simply transferred to make one object positive and the other negative, the total number of electrons and protons remains the same (equal), so the net charge is still zero. Now that we have created two objects of opposite charge, guess what? They'll attract! Because opposites don't only attract in real life; opposites attract in physics too. :] We would actually be able to calculate the electrostatic force that my hair would exert on the balloon using the equation 
F = kQ₁Q₂ /r² where k is equal to 8.99 x 10⁹ N • m²/C², Q₁ and Q₂ are the charges of my hair and the balloon, and r is the distance between them. I actually recall doing this as an experiment back in elementary school, but only now do I actually know the physics behind it (after, like, six years... Haha.)

[The Ninth Blog] Thermodynamics.

Since finals ended, I haven’t really thought about school. At all. Even though it’s only been, like, five days since we’ve been in physics class, I’ve basically forgotten everything. Well, not everything, but quite a bit. I’m forgetful, what can I say? :] 

I baked some pumpkin muffins this weekend. For Christmas, one of our neighbors gave us a jar of pumpkin bread/muffin mix with raisins in it that I finally decided to use on Saturday. They actually turned out to be pretty good. And the process involved physics, so all the better, right?

From the very beginning, physics was at play: when I set the oven to 350°, heat was added to the system in order to bring it up to temperature. Such a process is isochoric, as the volume of the oven cannot be changed. According to the ideal gas law PV = nRT, as temperature rose, so too did pressure. Also occurring due to the added heat was an increase in the system’s entropy.

Once the oven had reached 350°, it was time to put in the muffins. Since heat readily flows from hot to cold, heat was transferred from the surrounding air to the muffins, causing them to undergo a temperature and phase change. At this point, the muffins were taking part in an isobaric process. As the temperature of the muffins increased, it caused them to rise as they baked, with temperature and volume varying but pressure constant. Once the muffins were brought up to the same temperature as the oven, they finished baking in an isothermal process. [I think...] The muffins dropped slightly in height (volume decreased) as they continued to cook, since pressure was increasing as the batter became more dense, completing its change from a liquid-like substance to a solid, and temperature was being held constant.

And voila! The result: delicious pumpkin-raisin muffins and a nice lesson in physics. :]

 

[What Was Supposed To Be...The Eighth Blog] Sound.

Wow, it’s been a while... So here’s the response on sound from December that I just never got around to posting:

Values/Calculations

Instrument

Violin

Properties

Chosen string: D

- Frequency: 294 Hz

- Vibrating length: 0.32 m

- Mass density: 9.375 x 10^-4 kg/m [mass = 0.30 g]

- Tension: 33.191 N

      

Frequencies Of Next Highest Harmonics

- Second harmonic: 588.00 Hz

- Third harmonic: 882.00 Hz

    

Analysis

Fingering Positions

The fingering positions correspond to where the frequencies for the next notes can be found.  When you press the string down with your finger, it decreases the vibrating length of the string.  This shorter length results in a higher frequency.  When placed in the correct position, the new frequency is that of a new note.  For example, in first position, placing your first finger on the D-string gives the note E while your second finger can give either the F♮or F#, depending on where it is placed.

To play an E on the D-string, the vibrating length is reduced by about 0.03 m, making the new length 0.29 m.  So when the new frequency is calculated, it comes out to 324.412 Hz (which is fairly close to the established 329.63 Hz...).

Plucking/Bowing Location

The plucking/bowing location is close to the bottom (by the bridge) node of the string.  At this location...all (or most of...many of...) the harmonics are likely to be heard! :]

Plucking Versus Bowing

When a string is plucked, energy is only applied for an instant so the sound diminishes quickly.  When it is bowed, energy is constantly applied so the note can be heard for a longer period.  After the initial sound of a plucked note is heard (with all of its frequencies), some of the higher frequencies are lost so only lower and fundamental frequencies can be heard until the sound is stopped altogether.  However, when a note is bowed, all frequencies are being heard together continuously, giving it greater depth.