Boom!

A random image of a nuclear power plant. Source: http://blog.panampost.com/wp-content/uploads/smiley-nuclear.jp

 

I have gone these past 18 years of my life thinking that anything that has to do with the word “nuclear” or “atomic” must be a bad thing. After learning about Hiroshima and Nagasaki, two atomic bombs that the United States dropped in Japan during World War II, anything “atomic” or “nuclear” could not be good for our world. As I learned more about nuclear physics, however, I discovered that nuclear fission, the process by which atomic bombs explode, actually has some good practical uses.

In recent years, the world has come to depend on nuclear reactions for fourteen percent of its electricity. If harnessed correctly, nuclear fission can be a great source of electrical power. At many power plants across the world, nuclear reactors split atoms in controlled nuclear fission reactions to generate power. Before we discuss how nuclear reactors control the reactions to generate electricity, we must answer an important question: what is nuclear fission? Put simply, nuclear fission, the splitting of an atom, occurs when neutrons are fired at a nucleus. Despite the strong force holding the nucleus together, neutrons are able to split it. When an atom splits, an extremely large amount of energy is released. The split parts of the atoms then crash into other nearby atoms, resulting in more nuclear fissions, a chain reaction so to speak. This is the same process which results in the large explosions present in atomic bombs.

If nuclear fission results in atomic bombs, surely power plants would not be able to handle such a process, right? Wrong. Nuclear reactors in power plants are able to control nuclear fission through numerous control measures. Control rods made of cadmium, hafnium, or boron, for example, are able to absorb neutrons so that they will not reach the atom in the first place. The nuclear reactor, thus, is able to control how many nuclear reactions take place and can prevent excessive chain reactions from happening, all while producing electrical power from nuclear reactions. Amazing, huh?

 

Blinded by Light!

A photo that I took looking out to Diamond Head while I was on my boat.

When I was out on my boat last week watching the sunset, I witnessed the scene above and felt that I needed to take a photo of it to capture the moment. Despite the fact that the photo does not look very bright, the light reflected off of the water was actually quite blinding. It was hard to focus on taking the photo with the large amount of glare, so my friend lent me his polarized sunglasses. Upon putting them on, the glare from the water decreased drastically and I was able to take the photo. Looking at the above scene, we can witness many different concepts related to the wave nature of light such as the Rayleigh Criterion, Brewster’s Angle, Interference, etc. For the purposes of this blog, however, I want to hone in on a topic that was essential for my friends sunglasses to block the glare from the water: polarization.

Before we begin the sunglass discussion, let’s answer the following question: What is polarization and what does it mean for light to be polarized? Light is a transverse electromagnetic wave that vibrates in multiple directions. Light in its natural state, emitted from the sun or a classroom light, is said to be unpolarized because its electric and magnetic waves are vibrating in multiple directions. The interesting thing about light is that, although it is originally unpolarized, light can be polarized through a variety of methods. That is, light can be manipulated such that it can vibrate in a single plane rather than in multiple planes. In this blog post, I will analyze the photo I have posted above to explain how light can be polarized by reflection and the reason why polarized sunglasses block glare.

It is common for light to be polarized after reflecting off of non-metallic surfaces like water. Non-metallic surfaces naturally reflect light in a way such that the majority of the waves reflected are polarized in a direction parallel to the surface. The light waves in the posted photo, therefore, are mostly vibrating in a horizontal orientation. Now that we understand how light is polarized by reflection, how do sunglasses drastically cut glare? Glasses use polarization filters which are able to select which type of polarized light to allow through. If the polarization filter is perpendicular to the direction of the polarized light, no light will be allowed through. If the polarization filter is parallel to the direction of the polarized light, all of the light will be allowed through. Given that the light from the water was mostly polarized in the horizontal direction and that my friend’s sunglasses cut a large portion of the glare, we can reason that the polarization filter in the sunglasses must have been somewhat angled against the polarization direction but not completely perpendicular to it.

This blog post is only a brief description of polarization and how it relates to the wave nature of light. The topic is so large and undoubtedly impossible to cover in one short blogpost, but I hope that I was able to better your understanding of physics!

Infinity Mirrors!

A panoramic shot of my bathroom.

The picture above is a photo of my house’s main bathroom. Exciting, right? It may not seem so exciting at first glance, but once you realize that there are two plane mirrors in the room, things start to get pretty crazy. What could be so exciting about two plane mirrors placed across from each other? Won’t you just see the image of the other mirror? Not quite. In fact, it gets much more complicated than that and the image calculations almost become impossible to perform.

A photo taken of the main plane mirror that allows me to see the oval-shaped mirror.

There are two mirrors in my bathroom: the large plane mirror on the main wall and the small oval-shaped plane mirror above the toilet. While brushing my teeth tonight thinking about what I should write for my physics blog about optics, I realized something strange about the two mirrors. As I was looking into the main plane mirror, I noticed that the oval-shaped mirror in the back seemed to show me a reflection of my back. That observation was intuitive, but what really intrigued me was the fact that there seemed to be an infinite series of mirrors in which I could see a small portion of my bathroom. The picture to the left shows a photo that I took of the main plane mirror. The photo of the main plane mirror allows me to see the oval-shaped mirror and an infinite series of oval-shaped mirrors inside of it.

How and why does this series of infinite mirrors appear? The reason lies behind arguably the most basic fact about plane mirrors: plane mirrors produce virtual images that seem to appear “behind” the mirror. Because the oval-shaped mirror and the large plane mirror are located across from each other, they keep making images of each other. Let’s follow the light path for a few steps so we understand how this happens. Light from in front of the main plane mirror travels to the plane mirror and produces a virtual image that appears “behind” the plane mirror. At the same time, light in front of the oval-shaped mirror (which is coming from the image of the main plane mirror) travels to the oval-

A photo taken of the oval-shaped mirror.

shaped mirror and produces a virtual image that appears “behind” the oval-shaped mirror. Essentially, the two mirrors in this situation and producing images of images. Inside those images are two mirrors, the main plane mirror and the oval-shaped mirror. This sequences of events happens over and over again, forming an infinite amount of mirror images. That is, the mirrors are making images of images, and the images that the mirrors form go on to make further images of the formed images! Phew, that was a mouthful.

Infinity mirrors are an interesting application of optics. Although infinity mirrors are not extremely useful for us in our day-to-day lives, they can produce stunning designs. Check out the image below of an artificially made infinity mirror placed above a bathroom sink. Without physics, bathrooms would be extremely boring.

Infinity mirror in a bathroom.

Saved by Magnetism!

A side view of my MagSafe charger plugged into my laptop.

Last weekend my sister left her MacBook Pro connected to its charger on our kitchen table. While I was sitting on my couch observing the physics-filled world, I heard my mom exclaim, “Why does she always leave her laptop here? One day someone is going to trip over that cord and the laptop is going to fall to the ground!” I corrected my mom about this statement for two reasons: one, because I am aware of Apple’s MagSafe technology that is related to the magnetism unit I just learned, and two, because I  am a die-hard Apple supporter and will do anything to praise their products. Building off of the iDevice charger blog post that I made last week, I thought that I would continue with a discussion about the design of MacBook Pro chargers.

FYI: The above photo is an up-close view of Apple’s new MagSafe 2 charger. The middle node notifies the charger that it is connected to the laptop, the inner-middle nodes transfer power to the laptop, and the outer nodes are ground connections so that you do not get shocked when you touch the charger.

So, what does Apple’s MagSafe charger technology have to do with physics anyway? In two words: a lot. For this blog post, we will focus primarily on the magnetic design features of the MagSafe chargers. When you bring the end of the MagSafe charger near the charging port of the MacBook Pro, the charger becomes attracted to the charging port, snaps into place, and begins to transfer charge to the laptop. What causes the attraction between the charger and the laptop boils down to the basics of magnetism. Magnets have two ends called north and south poles. Similar to electric charge, likes repel and opposites attract. That is, north and south poles will attract each other while like poles will repel each other. Given this information, what can we conclude about the poles of the charger and the laptop charging port? Because the two attract each other, the poles must be opposite: one must be north and the other must be south. The idea to create a magnetic charger was extremely profound. Through Apple’s practical application of magnetism, they were able to create a charger that would save humans (from tripping) and Macbook Pros (from falling) alike.

This discussion of chargers leads me to another profound application of physics on Apple’s part. Apple’s MacBook Pro chargers output only 18.5 volts, yet the voltage supplied in a typical American power outlet is 120 volts. How does such a large voltage drop occur? Amazingly enough, Apple’s MacBook Pro chargers have tiny transformers inside of them that can transform a high voltage/low current situation into a low voltage/high current situation. Transformers achieve this phenomenon through alternating current and varying magnetic fields, which allows them to adjust voltage and current accordingly to suit the device’s power needs.

Who knew that magnets had better uses other than being toys for children who try to stick their same poles together? If you did not already know of some of their practical uses, I hope I have now educated you. If I have not, feel free to continue sticking like poles of magnets together to see how that works out for you.

The Physics of iDevice Chargers!

iPhone charger (left) and iPad charger (right).

A few days ago before I went to bed, I could not find my iPad charger for the life of me. Although I did not have an iPad charger handy, I found an extra iPhone charger on the floor of my room. Perfect, I thought, surely there is not that much of a difference between the two chargers. To my surprise, I was wrong. When I woke up the following morning I found that my iPad was only fifty percent charged. Why is it that my iPad can charge in about a night on the iPad charger but not on the iPhone charger? The simple answer comes down to basic current electricity.

Source	Voltage (V=IR)	Current (I=V/R)	Power (P=IV)
USB Port	5 volts	0.5 amps	2.5 watts
iPhone Charger	5 volts	1.0 amps	5 watts
iPad Charger	5 volts	2.0 amps	10 watts

The table above shows the values of voltage, current, and power for three different types of chargers that can be used to charge an iPad. Although voltage may be the same, current differs, which is the main value we are concerned with when it comes to charging our precious iDevices. From a quick glance at the table, we see that the current of the iPad charger is twice the current of the iPhone charger. After this observation, the reason why my iPad took so long to charge with the iPhone charger becomes clear.

Let us assume that I can normally charge my iPad from 0%-100% in about five hours using the 2amp iPad charger. If we decrease the current and power by half by connecting the iPad to the iPhone charger, the iPad takes about twice the amount of time to fully charge (about 10 hours) than it would take on the iPad charger. Even worse, if I decided to charge my iPad through my computer’s USB port, it would take about four times the amount of time to charge (about 20 hours) than it would take on the iPad charger because USB current is only 1/4 that of the iPad charger.

If the iPad charger is the clear winner in terms of charging time, why not use the iPad charger for all of your iDevices? Theoretically, you could. Apple uses the same voltage on almost all of their iDevice chargers so that people can use them interchangeably. So, why not just buy all iPad chargers? In short, it is not necessary. Why waste money on electricity to charge your iPhone with a 10amp iPad charger instead of a 5watt iPhone charger when your iPhone would finish charging at relatively equal times with both? Supplying more current to the iPhone will not make it charge faster. Although the iPad charger has twice as much current as the iPhone charger, the iPhone battery circuit only takes the amount of current that it needs (around 1amp) so that it does not overheat. In many devices nowadays, oversupplying current is not a problem. Undersupplying current for rechargeable devices, however, can dramatically increase charging time.

Now that you have basic knowledge about iPad and iPhone chargers, you may want to think twice before using them interchangeably.

Eraser Shaving Magic!

A photo of my AP Economics text book with eraser shavings on its cover. Little did those eraser shavings know that they would soon be flying to my pencil!

In AP Economics last week, Justin Park and I were sitting next to each other working on a worksheet that Colonel had given us. After realizing that we had made a mistake, I used my eraser to correct the error and then brushed the eraser shavings onto the table. Having just learned about static electricity, I was curious to see whether I would be able to magically pick up the eraser shavings with my pencil by using statics. As I was rubbing my mechanical pencil through my hair, Justin looked at me as if I were crazy. Confused, he asked me, “What are you doing?” I explained to him that I was experimenting with static electricity and then asked him if he remembered anything about statics from AP Physics B. When he replied, “No,” I saw a perfect opportunity to re-educate him.

I began my explanation to Justin about static electricity by telling him that it is possible to charge two items by friction. What does this mean, you ask? It means that it is possible to rub two objects together to cause one to be charged positively and the other to be charged negatively. Charging by friction works because electrons have a tendency to prefer one type of object over another, a strange and amazingly useful phenomenon really. How did I know that rubbing my mechanical pencil in my hair would cause one object to become positive and the other to become

A sample Triboelectric Series. Items on top have a tendency to charge positive while items on the bottom have a tendency to charge negative.

negative? I know because of a handy list called the Triboelectric Series, a list that ranks the tendencies of objects to become negative or positive when charged by friction. The photo to the left is a Triboelectric Series and shows that, when two objects are rubbed together, the object on top will become positive (lose electrons) while the object on the bottom will become negative (gain electrons). This list also shows a pattern: objects on the top tend to be natural objects (air, human skin, hair) while objects on the bottom tend to be artificial or synthesized (PVC, polyester, teflon).

Now that we have a basic understanding of static electricity and the Triboelectric Series, we can explain why I was able to pick up the eraser shavings with my pencil. When I rubbed my hard-plastic mechanical pencil through my hair, my hair became positively charged and my pencil became negatively charged. After charging my pencil, I waved it over the eraser shavings and witnessed the shavings levitate off the table and stick on and bounce off my pencil. The fact that I was able to move the eraser shavings may seem strange at first because I only charged the pencil, not the shavings. Justin seemed confused, so I explained to him that the eraser shavings need not be charged because they are neutral. If a charged object comes in close contact with a neutral object, they will still attract because the neutral object has an abundance of both protons and electrons. In this case, the protons in the eraser shavings were attracted to the negatively charged mechanical pencil, causing the entire eraser shaving to fly up and stick to my pencil.

Justin confided to me that he does not remember much about electricity and magnetism because they were very difficult topics for him. I told him not to worry, I will always be here to re-educate him about electricity and magnetism whenever he wants as I find picking up eraser shavings with my negatively charged mechanical pencil extremely fascinating.

Turn on the Radio!

A photo of my radio tuned to Power 104,300,000 Hz.

As soon as I sat down in my car today to go for a drive, I tuned my radio to Power 104.3 and heard the sweet sound of Taylor Swift’s “I Knew You Were Trouble” blasting through the speakers. Throughout all of the year’s that I’ve listened to the radio, I’ve always asked myself, “Why am I hearing this broadcast and why do I hear different broadcasts when I change the number on my radio’s tuner?” I always knew that radios worked because of transmission and reception of sound waves in the air, but, to be honest, I barely knew what a sound wave even was. Now, with sufficient knowledge of the physics of sound, I can easily explain to myself (and to all of you readers if you’d like) how you too can hear Taylor Swift blasting through your radio’s speakers.

A photo of me and a Taylor Swift life-size cut out.

When you tune your car’s radio to a radio station, for example, Power 104.3, have you ever asked yourself what those numbers actually mean? I didn’t think so. 104.3 is short for 104.3 MHz (megahertz.) That is, 104,300,000 Hz. Hertz, as we all know, is a frequency, represented by the equation f=1/T, where T is the period, the amount of time a sound wave takes to make a complete oscillation. We don’t necessarily need to know this, but the period of Power 104.3’s sound wave is T=1/104,300,000Hz=9.58×10^-9s, now that is one fast period! It makes sense that an FM radio station’s period would be so fast, it needs to transmit a lot of information really quickly in order to make a high quality broadcast. This explains why AM stations are not as high quality as FM stations, AM frequencies are only in kHZ as opposed to MHz.

Now that we’ve explained the basics of frequencies and periods of sound waves, how does your radio pick up these waves and relay their broadcast to your speakers? This is simple. Let’s use Power 104.3 as our example. Power 104.3’s transmitter’s sine wave has a frequency of 104.3MHz as previously stated. That’s great. We have a really fast sine wave moving through the air. Now what? Your car’s radio has a receiver complete with an antenna, tuner, and an amplifier. The radio receiver’s antenna picks up all of the radio sine waves traveling through the air. The tuner’s job is to then separate the one sine wave you want from all of the other sine waves. In our case, the tuner separated the 104.3MHz sound wave from all of the others. You may be asking, how does the tuner do this? That’s simple too. Tuners work using a principle called resonance. That is, the tuner resonates at one particular frequency and ignores all other frequencies in the air. Finally, the tuner sends the signal that it receives from a particular frequency to the radio’s amplifier, which ultimately amplifies the sine waves to your car’s speakers. Viola!

There you have it everyone, the physics of radios. Look above you! You see those? Those are radio waves. Thousands of them. Care to listen? Tell your tuner to resonate where you want it to!

A HOT Marathon!

Today I ran the 26.2-mile Honolulu Marathon and realized what pain is for the first time. Never before had I felt so tired, beat-down, and helpless. To my delight, everything was going just fine for the first half of the race. Then to my dismay, a couple things changed: the sun came up and I felt as if I could barely walk on my knee. What was I going to do? I really wanted to finish the marathon and wear my finisher shirt with pride, so I forced myself to keep pushing. Although it was extremely hot, there were water and ice stations throughout the race which cooled me down (stole some of my body’s heat). Having just taken my AP Physics B Thermodynamics test on Friday, I started to mentally explain to myself why I was hot and why the ice cooled me and my injured knee down. Heat is transferred by three main mechanisms: radiation, convection and conduction, all of which I experienced today. It really is just simple Thermodynamics.

A photo of me rounding a corner in Hawaii Kai.

The reason why I became hot when the sun came up is because of radiation, the movement of energetic waves or particles. The sun’s rays, forcefully beating down on me as I ran, undoubtedly heated me up a bit. The sun did not just heat me up, however, it heated up the black asphalt, which then heated me up even more.

The reason why the black asphalt heated me up is because of convection, the movement of molecules in fluids. The black asphalt absorbed a large amount of heat from the sun’s radiation and then transferred that heat in the air through convection. No wonder why it was so hot running on asphalt as opposed to when I was running on grass; grass does not absorb heat as well as asphalt!

Although radiation and convection were heating me up like crazy, I was able to cool myself down with some ice that I found at water and ice stations throughout the race. Hot, tired, and feeling dead, I grabbed a handful of ice from the aid station and rubbed it on my knee and neck. Why did I feel as if the temperature of my leg and kneck were getting lower? Obviously there was some conduction (the transfer of heat through matter) going on here. When I put the ice on me, heat immediately started to transfer from my body to the ice cube, ultimately melting the ice cube. The poor ice cube was not receiving heat just from my body, it was receiving heat from the same radiation and convection that I was experiencing too! Poor ice cube 😦

My ice cubes weren’t the only things that melted today. My heart melted when, to my surprise, Jordan was waiting for me at the finish line 🙂 Would that be radiation, convection, or conduction? I don’t know.

During the race, I wished that the laws of thermodynamics did not apply to ice cubes. If the ice never melted, I would’ve been a lot more comfortable when I was running. Oh well. Although the marathon was probably the hardest thing I’ve done in my whole life, I’m glad that I did it and I’m thankful to be sitting in my air-conditioned room as I write this week’s physics blog. Tired and worn-out, I’m having trouble thinking right now, so let’s save the discussion on air conditioning for another time.

Paddling in the Deep Blue Fluid!

A calm Saturday morning before the start of a paddling race.

Ah yes, it’s that time of year again: paddling season. A time for boys to become men, a time to take the next stroke and paddle out into the uncertain blue sea. Although `Iolani Mens Paddling does not usually place well in the races, I and the rest of my crew enjoy it and continue to paddle out every day into the world’s most vast body of fluid: the ocean. The ocean is a fluid of uncertainty, you never know what you are going to encounter and you never  know how it is going to treat you. In this large fluid of uncertainty, there is one thing that’s for sure: we’ll all float on.

What is this concept of floating? Why is the canoe “buoyant“? In the most basic terms, the canoe floats because it is less dense than water. That is, the mass of the canoe over the canoe’s volume exists in a ratio such that it’s density is not greater than 1027 kg/m^3 (the density of sea water). More technically, the boat floats because there is an upward buoyant force pushing up on the boat that is equal to it’s weight. That is, Fb = ρVg = mg, where ρ is the density of the fluid, V is the volume of the object displaced in the fluid, g is gravity, and m is the mass of the object. Wait a minute, I thought that the floating canoe depended on it’s density, not it’s volume! How come buoyant force doesn’t factor in the object’s density? In short, it does. The V in the buoyant force equation can be rewritten as m/ρ_object = V. As long as the canoe is less dense than sea water, we’ll have a buoyant force equal to our weight, keeping us happily floating along.

That’s great that the canoe has a density greater than that of ocean water! That means that we won’t ever sink in races, right? Unfortunately, wrong. As previously mentioned, density depends on mass/volume. What would happen to the canoe, for example, if a rogue wave were to fill it with water while we were paddling (unfortunately, this has actually happened before, but we ended up alright)? Let’s think about this, as the canoe fills with water, it’s mass increases. What’s happening to it’s volume? Nothing. That’s the problem. As the mass of the canoe increases but its volume remains constant, its density increases. Once the canoe becomes more dense than ocean water, it will begin to sink. In paddling, we call this getting “swamped”. Once it begins to sink, buoyant force is no longer  Fb = ρVg = mg, it is  Fb = ρVg = mg – mg_apparent. Luckily, if we flip the canoe over and empty the water out, its density will again be less than that of ocean water. Hooray! We survived 🙂 

A photo of me and Terry Lam after surviving a life threatening paddle.

Phew, thank goodness for buoyant force.

Don’t Fall, Balance!

My Precalculus book providing a negative clockwise torque.

After coming home from a long school day, I carelessly threw my Precalculus and AP Economics textbooks on my desk. They landed in a peculiar fashion in which the AP Economics book was almost all the way off the edge of the table and the Precalculus book was on top of it. That’s strange, assuming the center of mass is located at the middle of the AP Economics book, shouldn’t it just fall off the table because most of it’s mass is over the edge? Of course not! The system, because of the Precalculus book on sitting on top of the AP Economics book, is in equilibrium. With knowledge of torque and equilibrium learned in AP Physics B, a situation like the two balancing textbooks is easy to explain.

Looking at the picture to the left, we choose the point below the second “c” on the AP Economics book to be the fulcrum. We can now analyze the forces acting on either side of the fulcrum to prove that the system is in equilibrium. To the left of the fulcrum, the (mass)(gravity) of the AP Economics book’s center of mass provides a positive counter-clockwise torque. To the right of the fulcrum, the (mass)(gravity) of the Precalculus book’s mass provides a negative clockwise torque. Knowing that the system is in equilibrium just by looking at it, we can conclude that the torque to the left of the fulcrum equals the torque to the right of the fulcrum. Because net torque in equilibrium is equal to zero, the system can be represented by the following equation: ΣΤ = 0 = (mg)(d2) – (mg)(d1). Recall that torque is equal to (force)(distance)(sin(theta)). In this scenario, theta is 90 degrees so it is simply equal to 1. If we were to rearrange the equation, we can easily see that the torques equal each other on both sides: (mg)(d1) = (mg)(d2).

Look what time it is! I think it’s time for me to do my math homework. If I remove the Precalculus book from the AP Economics book, what is going to happen? Well, removing the Precalculus book will remove the negative clockwise torque, leaving only the positive counter-clockwise torque of the AP Economics book’s center of mass. Because there is nothing to balance the AP Economics book’s torque after I remove the Precalculus book, the AP Economics book is bound to fall. Indeed, after I removed the Precalculus book from the AP Economics book, the latter came crashing to the ground off my desk. Some of my friends would probably be frightened by how I can relate such a simple thing like balancing books to Physics, but that’s just the way I do things.