Tips on how to study a STEM subject, from a physics student
1. Go to class
Going to class and paying attention is key in this kind of subjects. I used to think that if I just read the notes I would understand the same, but this is a mistake. It took me way longer to grasp the concepts than if I had simply listened to my professor.
2. Understand the theory
I thought that jumping straight into doing exercises was easier to do and would prepare me for the exam, but this is a mistake. I found myself struggling with most problems just because I hadn’t understood the theory behind them.
3. Exercises
When you feel that you get the concepts you can jump into the exercises. Do as many as you can, and try to really understand where you make mistakes and how your teacher’s solutions differ from yours. I recommend you do them when the exam is close, so you have all of them fresh in your memory.
4. Practice exams
This is the last thing you should do before the exam, and it is optional, just do it if you are really pushing for that A. Pretend it’s a real one and it will really make you feel confident when the actual day comes.
Leiden physicist Milan Allan and his group have discovered an apparent paradox within a material that has zero electrical resistance. They report trapped charges, although charges should, in theory, keep flowing in the absence of resistance. The discovery could provide a missing piece of one of the big puzzles in physics today—high-temperature superconductivity. The results are published in Nature Physics.
A material can either be insulating or conductive. In an insulator, an extra electron will get trapped. Thus, no electric current flows in insulators. In a conductor, extra electrons will immediately flow. The more conductive the material is, the faster the electrons will flow.
The research group of Leiden physicist Milan Allan was therefore surprised to discover charge trapping in a material with zero resistance. Charge trapping is supposed to be a telltale sign of an insulator. Together with Leiden theoretical physicist Jan Zaanen, Allan’s group found that the phenomenon could unravel a longstanding mystery about charge transport in a family of materials called cuprates. These poorly understood materials have no resistance, even at relatively high temperatures, and are therefore labeled high-temperature superconductors. The mechanism behind those is one of the big mysteries in physics today.
When seeing this picture you may think wow that’s gotta’ be painful! and you’re right! It is indeed painful but it’s bearable. Why?
Well, pressure is defined as the ratio of force to the area over which that force is distributed.
P = F/A
One can also say that pressure is force per unit applied in a direction perpendicular to the surface of an object.
Looking back at the picture, we can see that the area is spread out enough so she can balance. If we pressed one single finger down on one spike, it would hurt much more than when we use our whole hand. Then again, both of those options would be painful and probably not the brightest thing to do!
‘Pressure’ is a key term in Thermal Physics, along with ‘Temperature’ and ‘Heat’. Thermal physics is the combined study of thermodynamics, statistical mechanics and kinetic theory.
We’re pretty much obsessed with Temperature, it’s an important part of our lives. I don’t know about you, but when I wake up to see it’s -10 Celsius outside it certainly makes me grumble. We’re so used to just looking at a thermometer that we might not stop and just wonder, howdoes that actually work?
Well, when two objects are in contact with each other, they will eventually both have the same temperature. This can be explained by the zeroth law of thermodynamics/Law of equal temperatures: An object that cannot change it’s own temperature, will eventually reach the same temperature as its surroundings. This is the idea behind our thermometers.
If you’re not familiar with Celsius than you may be familiar with Fahrenheit instead. However, most of us, if not all, are familiar with Kelvin. Absolute zero is defined as a temperature of 0 Kelvin, which is equal to -273.15 Celsius or -459.67 Fahrenheit.
So let’s say you’re more fortunate than I am, with a thermometer that shows a higher temperature. You might say you’re “warm”. In Physics this word is used differently, it’d be more accurate to say: “I’ve got too much internal energy right now!“ In my case it’d be "I really really reaaaallly need more internal energy, help”.
Picture above: A map of global long term monthly average surface air temperature.
What CAN we say about heat, what IS heat?
Heat is defined as energy transferred from one body to another by thermal interactions. Heat has the symbol Q and the SI-unit (for those who don’t know what that is: http://en.wikipedia.org/wiki/International_System_of_Units) J for Joule.
Heat flows from systems of higher temperatures to systems of lower temperatures. When two systems come into thermal contact, they then exchange energy through the microscopic interactions of their particles.
Heat is also necessary when we use the first law of thermodynamics. Which states: The increase in internal energy of a closed system is equal to the difference of the heat supplied to the system and the work done by it:
ΔU = Q - W
Now that we’ve established that heat flows from systems of higher temperature to systems of lower temperatures, can it be reversed? That’s where the Second law of Thermodynamics comes in: Heat cannot spontaneously flow from a colder location to a hotter location.
We also know that energy cannot be created nor can it disappear. So what happens? We have different energy qualities. High energy qualities and low energy qualities. The problem is that a low energy quality cannot turn into a high energy quality, what can happen is that energy is used and transformed and after a while turns into energy with a lower quality. It does not disappear but after a while it pretty much becomes unusable. This is one of the theories of the Universes ‘death’, that in many many maaaany years to come, there will not be any high quality energy left, only unusable energy with a too low quality.
Aren’t all of them the same? No, they’re quite different actually. The confusion lies mostly around the fact that both Speed and Velocity are measured by m/s (meters per second) and Acceleration measured by m/s^2. This does not mean they’re the same though.
Speed is the rate of motion/rate of change of position. It doesn’t have a specific direction. Therefor, speed is a scalar quantity expressed as distance moved per unit of time. Speed is the magnitude component of velocity. Velocity contains both the magnitude and direction components and is a vector quantity.
When we talk about how fast something moves, we mean how far it can move in a given time, whilst when we talk about acceleration, we mean how the velocity changes in a given time.
How do we measure speed?
Galileo Galilei is said to be the first to measure speed by considering the distance covered and the time it takes. He defined speed as the distance covered per unit of time. As an equation:
Here, v is velocity, d is distance and t is time.
This equation is simple but very useful. You can find the velocity, distance and time by using this equation (providing you know 2 of the components). However, as this equation is simple, the velocity has to be constant (the speed is always the same). This might seem unrealistic, but it’s very precise.
Picture above: A graph showing the distance, time and constant speed. The time is on the X-axis, whilst the distance is on the Y-axis. We usually use m/s for velocity (meters per second).
Velocity as you most likely know, cannot always be constant. This is when instantaneous speed comes in. Instantaneous speed is the velocity of an object at a certain time. The graph below is an example of measuring instantaneous speed.
In the picture above there are tangents drawn across the points in time, in order to find the speed. You then calculate (for example, here they divide Delta Xp with Delta Tp on both tangents) the slope for the new tangent(s) you have drawn and get the instantaneous speed. There are faster ways to calculate the instantaneous speed but those require more advanced equations and mathematics.
When the speed varies with time, the movement is accelerated. You can have both positive and negative acceleration. For example, when a car stops, the velocity sinks and therefor the acceleration becomes negative. When a car increases it’s velocity, the acceleration becomes positive.
In Physics, we also use constant acceleration. This equation can be used to find the acceleration, start velocity, end velocity and time:
Usually there is a line above the “a” to point out that it’s the constant acceleration.
Picture above: Here we see the different types of graphs for Position, Velocity and Acceleration.
One of the greatest questions of all time, has to be “whatIStime?”.
Is time defined by what we see on our mechanical clocks? Does time stop? Does time have a constant speed? Does time have a beginning and end? There are countless questions we can ask about time but what are the answers?
We are all familiar with time, our whole lives revolve around it. Yet, we don’t know everything there is to know about it. We can start by measuring time.
Hours, minutes and seconds were first adopted by the Babylonians, some say they even invented time. However, they could have never actually invented time but they made a system for time. The days were 12 hours and the nights 12 hours. The hours were broken down into 60 minutes and those that needed even more precise numbers, they broke down those 60 minutes into 60 equally big parts (60*60=3600 seconds).
To measure the time they used the human heart-beat, one second was the duration of time between the two heart-beats of a healthy human (in a relaxed state).
The first mechanical clocks were invented in the 1200s. They had a pendulum that swung back and forth. There are different types of clocks and therefor the clocks we use in our everyday lives are referred to as mechanical clocks. Biological clocks are quite important to us, the heart-beat is an example of a biological clock and even a woman’s menstrual cycle is a biological clock (probably not the kind of clock you’d want to watch).
Today we also use atomic clocks, they’re so precise that they will either speed up or slow down by one second in a million years. They’re based on specific type of radiation from the Cesium atom. The Second is now defined by this radiation and perhaps in some years we’ll invent even better clocks with yet another definition of time. However by current definition, a second is the duration 9,192,631,770 cycles of radiation in a transition, or energy level change, of the Cesium atom.
Picture above: A pendulum showing the acceleration (a) and velocity (v) vectors.
Is time a vector or scalar quantity?
Firstly, scalars are quantities that are fully described by a magnitude alone (Time and Mass) Vectors are quantities that are fully described by both a magnitude and a direction (Velocity and Force).
Time is said not to have any direction, only magnitude. Therefor it is a scalar quantity.
Another question that tends to puzzle humanity is about space and it’s length. Is space endless? Has it always existed? Is space just the distance between two objects or is it something more? If you took away ever last atom and object, would there still be space or would there be nothing? Even then you can ask, what IS nothing? Does ‘nothing’ exist?
One thing is for sure, we can measure length. There are many different measurements for length all over the world; Feet, yards, centimeters, etc. However the result is always the same, no matter how you measure. The distance that is there, is there and will not change no matter which measurement you decide to use. However, the international measurement tends to be in meters. The meter is defined by the movement of light.
A meteris the length of light moving in free space during a time interval of 1/299 792 458 of a second.
Why do we use light to define certain measurements? The light speed in a vacuum is the same no matter when or where we measure and it doesn’t even matter if the light source is moving relative to us.
It’s extremely hard to be 100% precise when talking about length and all length measurements are a little uncertain. Your height for example, let’s say your height is 162 cm. That means you’re between 161,5 cm and 162,5 cm. However, we’re getting better and better at being even more precise and inventing new measurements that will help us in the future.
The muon and tau are second and third generation, respectively, leptons and fermions. There are a total of 6 leptons in the standard model. The electron, muon, and tau are the three which have electric charge while the others, the neutrinos, do not. Both the muon and tau are much more massive than the electron and decaydue to the weak interaction. The muon decays on average 2.2 microseconds (2.2*10^-6 s) into usually an electron and two neutrinos of different types. The tau decays much quicker in 2.9 * 10^-13 seconds into hadrons(composite particles made of two or more quarks, e.g. proton). The tau is the only lepton able to decay into hadrons because it is the only one with sufficient mass.
The muon was discovered by Carl D. Anderson and Seth Neddermeyer in 1936 by studying cosmic radiation and observed particles which deflecteddifferently than electrons in a magnetic field. The radius of deflection depends on mass and charge. Since the charge is the same the difference must be accounted through a greater mass.
The tau was theoretically predicted in 1971 by Yung-su Tsai and experimentally detected between 1974-1977 at the Stanford Linear AcceleratorandLawrence Berkeley National Laboratory.
Probably the most well known experiment that involves muons is the Muon g-2 (”g minus 2″) experiment at the Fermi National Accelerator Laboratory or Fermilab. The goal is to measure the magnetic dipole moment at a very high precision because there is a slight deviation from g=2 (hence g minus 2) known as the “anomalous” part predicted by the Standard Model theory. A large enough difference between the experimentally measured and theoretically determined values could point to the existence of more undiscovered subatomic particles. Read more about the Muon g-2 experiment below:
The electron is a first generation fermionand a lepton. Fermions are particles with have half-integer spinthat follow Fermi-Dirac statistics and obey the Pauli exclusion principle. The Pauli exclusion principle states that two identical fermions can’t occupy the same quantum state (i.e. have the same quantum numbers within a quantum system). Leptons are a subcategory within fermions that can exist independently (without binding together) and do not interact through the strong force unlike quarks. Lastly the generations of the fermions loosely refers to the higher masses for particles in higher generations.
The existence of electrons was first discovered by J.J. Thompson in 1897 when he experimented with cathode ray tubes like the one depicted above. By applying electric and magnetic fields across the cathode ray Thompson was able to determine the mass-to-charge ratio of the particles in the cathode ray. With this he found that the particles were much smaller than any atom and by testing different sources, these negatively charged particles exist in every element.
Electrons are one of the primary charge carriers in atoms alongside protons but are the primary contributors to electric current. Electrons also have an intrinsic property known as spin which contributes to paramagnetismin certain materials.
Above is a video of an electron riding a light wave. The video was taken using a stroboscope which captures. More on it here (article)andhere (video).
Research involving electrons covers almost every corner of modern physics from high energy particle physics to condensed matter physics and even quantum computing. I have linked articles on recent research with a focus on electrons below for further reading.
Why is breath sometimes cold and sometimes warm? (”hoo vs. haa”)
Hold your hand about a half foot (15 cm) from your mouth and open your mouth wide and blow air like you are fogging up a mirror. (”haa”) Your breath should feel warm. Now purse your lips and blow out. (”hoo”) Your breath should now feel cold. If you bring your hand closer to your mouth by about a centimeter away and blow out through pursed lips then your breath should feel warm again. Why is this?
The air from your exhale is generally warmer than the ambient air outside your mouth. When your lips are pursed then the air is moving at higher speeds than with your mouth open. At these higher speeds the air from the exhale drags along the cooler still air due to friction. The breath air thus is doing work on this cooler so it also looses energy resulting in lower temperature. So overall the added cooler air and decreased temperature makes your breath feel cooler.
At distances closer to your mouth the warm breath air has yet to lose enough energy or drag along any cooler air so the breath still feels warm. With your mouth open the air is slower and takes up a larger volume so the majority of the air that reaches your hand is warm.
University of Chicago scientists are part of an international research team that has discovered superconductivity–the ability to conduct electricity perfectly–at the highest temperatures ever recorded.
[…]
Using advanced technology at UChicago-affiliated Argonne National Laboratory, the team studied a class of materials in which they observed superconductivity at temperatures of about minus-23 degrees Celsius (minus-9 degrees Fahrenheit)–a jump of about 50 degrees compared to the previous confirmed record.
Though the superconductivity happened under extremely high pressure, the result still represents a big step toward creating superconductivity at room temperature–the ultimate goal for scientists to be able to use this phenomenon for advanced technologies. The results were published May 23 in the journal Nature; Vitali Prakapenka, a research professor at the University of Chicago, and Eran Greenberg, a postdoctoral scholar at the University of Chicago, are co-authors of the research.
Many of you may recognize this photo of the x-ray diffraction pattern of DNA found by Rosalind Franklin and her PhD student, Raymond Gosling. But, you may wonder how one could figure out from this image that DNA is structured as a double helix and even how x-ray crystallography works.
X-Ray Crystallography
X-ray crystallography is a method of determining the positions and arrangements of atoms in a crystal. Crystals are usually defined to be a highly ordered and repeating microscopic structure of a solid rather than the macroscopic crystals we know like quartz which actually tend to be “polycrystals” because at a microscopic level they do have the highly ordered structure required. Ice is also a polycrystal composed of many smaller ice crystals.
1.) X-ray beams are shot at the crystals
The x-rays interact with electrons of the atoms. This interaction or collision is typically modeled by Thomson scattering where the energy and thus frequency of the x-rays do not change after diffraction. This is similar to light going through a diffraction grating.
2.) Beam is diffracted
The x-rays are diffracted based on the crystal lattice structure of the substance. This is dependent on the characteristics of the bonds between atoms like the bond angles and bond lengths. Also the spacing between molecules also determines the diffraction.
3.) Diffraction pattern
The diffracted x-rays are light waves so they interfere both constructively and destructively. The resulting intensities of the x-rays are recorded on a screen behind the sample to create a diffraction pattern. The sample is rotated to take more data. After sufficient data is taken a model for the crystal structure for the sample can be developed. With a diffraction pattern an electron density map can be made which depicts the location and size of electron clouds in the substance.
One hundred years ago, Einstein’s theory of general relativity was supported by the results of a solar eclipse experiment. Even before that, Einstein had developed the theory of special relativity — a way of understanding how light travels through space.
Particles of light — photons — travel through a vacuum at a constant pace of more than 670 million miles per hour.
All across space, from black holes to our near-Earth environment, particles are being accelerated to incredible speeds — some even reaching 99.9% the speed of light! By studying these super fast particles, we can learn more about our galactic neighborhood.
Here are three ways particles can accelerate:
1) Electromagnetic Fields!
Electromagnetic fields are the same forces that keep magnets on your fridge! The two components — electric and magnetic fields — work together to whisk particles at super fast speeds throughout the universe. In the right conditions, electromagnetic fields can accelerate particles at near-light-speed.
We can harness electric fields to accelerate particles to similar speeds on Earth! Particle accelerators, like the Large Hadron Collider and Fermilab, use pulsed electromagnetic fields to smash together particles and produce collisions with immense amounts of energy. These experiments help scientists understand the Big Bang and how it shaped the universe!
2) Magnetic Explosions!
Magnetic fields are everywhere in space, encircling Earth and spanning the solar system. When these magnetic fields run into each other, they can become tangled. When the tension between the crossed lines becomes too great, the lines explosively snap and realign in a process known as magnetic reconnection. Scientists suspect this is one way that particles — for example, the solar wind, which is the constant stream of charged particles from the Sun — are sped up to super fast speeds.
When magnetic reconnection occurs on the side of Earth facing away from the Sun, the particles can be hurled into Earth’s upper atmosphere where they spark the auroras.
3) Wave-Particle Interactions!
Particles can be accelerated by interactions with electromagnetic waves, called wave-particle interactions. When electromagnetic waves collide, their fields can become compressed. Charged particles bounce back and forth between the waves, like a ball bouncing between two merging walls. These types of interactions are constantly occurring in near-Earth space and are responsible for damaging electronics on spacecraft and satellites in space.
Wave-particle interactions might also be responsible for accelerating some cosmic rays from outside our solar system. After a supernova explosion, a hot, dense shell of compressed gas called a blast wave is ejected away from the stellar core. Wave-particle interactions in these bubbles can launch high-energy cosmic rays at 99.6% the speed of light.
Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.
As someone who used to play the bass guitar, I can’t believe I didn’t know how a guitarpickup works. The basic idea is actually relatively simple but the complexity comes when engineering the sound we hear from Jimi Hendrix, Jimmy Page, and B.B. King.
The mechanism is centered around Faraday’s Law of Induction. The guitar pickup in its simplest form is a permanent magnet(s) wrapped in a coil of wire. A permanent magnet is made from a ferromagnetic material (like iron) which is a special type of material where the “magnetic domains” are aligned with an external applied magnetic field.
The role of the permanent magnet is to magnetize the guitar string because it is also a ferromagnetic material like nickel or steel. When you pluck the string it vibrates and results in an oscillating(changing)magnetic flux through the coil. Because of Faraday’s Law of Induction this induces a signal(changing voltage) and thus current which is read by the amp to reverse engineer it into sound. Check out thisappletfrom the National High Magnetic Field Laboratory for a visual.
Since the string’s movement determines the signal picked up, the pickups receive a strong signal when directly under a part of the string moving with a large amplitude and frequency. So when it is directly under a node(where the string doesn’t move) like in the above picture (for the 7th harmonic), one of the pickups gets a very weak or possibly no signal. So in a way the pickups act as filtersfor the different harmonics depending on their placements which is key to the sounds we hear in the music. So as you can see the exact engineering can become extremely complicated
Scientists from Lawrence Livermore National Laboratory (LLNL) used giant lasers to flash-freeze water into its exotic superionic phase and record X-ray diffraction patterns to identify its atomic structure for the very first time—all in just a few billionths of a second. The findings are reported today in Nature.
In 1988, scientists first predicted that waterwould transition to an exotic state of matter characterized by the coexistence of a solid lattice of oxygen and liquid-like hydrogen—superionic ice—when subjected to the extreme pressures and temperatures that exist in the interior of water-rich giant planets like Uranus and Neptune. These predictions remained in place until 2018, when a team led by scientists from LLNL presented the first experimental evidence for this strange state of water.
Now, the LLNL scientists describe new results. Using laser-driven shockwaves and in-situ X-ray diffraction, they observe the nucleation of a crystalline lattice of oxygen in a few billionths of a second, revealing for the first time the microscopic structure of superionic ice.
Richard P. Feynman an astounding theoretical physicist and professor
∆ Quantum mechanics & particle physics
∆ Quantum electrodynamics (QED) for which he shared a Nobel Prize
∆ Superfluidity of liquid helium
The diagram above is of a vector boson fusion producing a Higgs boson. Feynman developed this method of representing particle interactions which have been important to the understanding of work in particle accelerators such as the Large Hadron Collider.
The following is a wonderful video of Feynman talking about light
By drilling holes into a thin two-dimensional sheet of hexagonal boron nitride with a gallium-focused ion beam, University of Oregon scientists have created artificial atoms that generate single photons.
[…]
The artificial atoms - which work in air and at room temperature - may be a big step in efforts to develop all-optical quantum computing, said UO physicist Benjamín J. Alemán, principal investigator of a study published in the journal Nano Letters.
“Our work provides a source of single photons that could act as carriers of quantum information or as qubits. We’ve patterned these sources, creating as many as we want, where we want,” said Alemán, a member of the UO’s Material Science Institute and Center for Optical, Molecular, and Quantum Science. “We’d like to pattern these single photon emitters into circuits or networks on a microchip so they can talk to each other, or to other existing qubits, like solid-state spins or superconducting circuit qubits.”
