Questions tagged [order-of-magnitude]

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What exactly is order of magnitude?

I am little bit confused with what order of magnitude is. In my book it says, when we write approximate values of quantities in powers of ten i.e $10^b$, then $10^b$ is the order of magnitude. But ...
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What does it mean that gravitation separated from the four forces at $10^{-36}$ seconds?

Physicists have used math to calculate that gravitation separated from the 4 forces at 10^-36 seconds after the big bang, which is even before the inflationary period. The universe was still smaller ...
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Steady Couette flow where the moving wall suddenly stops

Let it be a planar Couette flow for an incompressible fluid with dynamic viscosity $\mu$ and density $\rho$ that has reached the steady-state. Assuming that the plates are placed at the $xz$ plane, ...
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Scaling difficulty of landing a rocket

I am wondering whether it is more difficult to land (as spaceX does) a rocket of height $k L$ than landing a rocket of height $L$? Is there some scaling law? Or at least is there a way to see in the ...
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Why is $\exp(-1)$ a good benchmark in many physics? [closed]

In many subjects in Physics (not only phys though), we often encounter a value which gives $\exp(-1)$, such as a time constant in circuitry ($\exp(-t/RC)$, $t=RC$ gives $exp(-1)$), lifetime, mean free ...
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Are neurons more energy efficient than transistors?

In terms of order of magnitude, how does a the energy consumption of a typical mammalian neuron (in the brain) compare with the state of the art MOSFET?
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1 vote
2 answers
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Explain the theory behind this problem(if possible using number line or graph or any other method of pictorial representation) [closed]

In a situation in which data are known to three significant digits, we write 6.379 m = 6.38 m and 6.374 = 6.37 m. When a number ends in 5, we arbitrarily choose to write 6.375 m = 6.38 m. We could ...
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Could the ITER central solenoid lift an aircraft carrier 2 m into the air?

This claim is made in many places around the internet, presumably repeated from an ITER press release. But are there caveats? Does the aircraft carrier need to be in water (so only the no-longer-...
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How many waves are in the ocean? [closed]

XKCD #2741 mentions in the title text It's cool how, when there's a number lots of people are curious about, but which isn't easy to measure, some random guess will get cited everywhere and become ...
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1 answer
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Is it just a coincidence that the range of order of magnitude of length and time is $10^{41}$ does it have some explanation?

The ratio of the longest and shortest lengths of objects in our universe is about $10^{41}$. Interestingly enough, the ratio of the longest and shortest time intervals associated with the events and ...
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Comparing the strength of gravity and electricity

I often see and hear people claiming that "the gravitational force is much weaker than the electromagnetic force". Usually, they justify it by comparing the universal gravity constant to ...
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How to incorporate HEP into the naive picture of QM?

When I explain QM to non-physicists, I sometimes say that quantum effects are typically noticeable on very small scales. For example, a QM particle in the harmonic potential behaves mostly classically,...
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What is the smallest time that the current technology can measure?

Many physical phenomena are associated with unbelievably small time scales. Let me give a few examples. The time scale associated with visible light is $\sim$ a femtosecond ($10^{-15}$ sec), The ...
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0 answers
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What is the value of electroweak scale? Depends on literature?

Depending on the literature, we see for the electroweak scale the following typical values : 100 GeV, 125 GeV (Higgs mass), 246 GeV (vev), 1 TeV So what is really the value of electroweak scale?
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2 answers
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Order of magnitude of zero?

I was wondering what exactly the order of magnitude is of 0. Just by calculating it you obviously get $-\infty$ because of the logarithm but is this really correct?
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What does the resistance of same order means in wheatstone bridge means?

As we know that in order to increase the sensitivity of wheat stone bridge resistance are of same order but here what exactly order means can anyone give me an example of this order?
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3 answers
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Understanding importance of Planck energy

Planck length is considered to be smallest length possible in the universe. Planck time is smallest time interval possible. Similarly what is importance of Planck energy because it is neither ...
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How do physicists compare the relative strengths of the four forces?

Since the four forces are different, with different force carriers, how are they (seemingly) directly compared? I often read that the weak force, for example, is many orders of magnitude stronger ...
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Nucleus vibration

What are the frequencies of the vibrations of the atom's nucleus? Is it in the quadrillions? Vibrating molecules is not the same thing - which is addressed as phonon vibration.
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-2 votes
1 answer
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Multiple levels of expansion of space? [closed]

It can easily be seen from the plot that there are at least 3 gaps between objects in the large, there is the gap between the planets and the moons, and between the planets and stars, and between ...
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Why is quantum gravity so tough to be proved experimentally?

A great deal of particle physics experiments are going on in CERN and similar experimental labs and their study is based on quantum field theory? But I could not understand why quantum gravity is so ...
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The answer to this question is not close to the age of the universe, then why do we say it is?

I saw this question in our textbook A great physicist of the century (P.A.M. Dirac) loved playing with numerical values of Fundamental constants of nature. This led him to an interesting ...
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Why does everyone seem to assume that gravitational waves will always be very small? [duplicate]

The size or effective distortion field of a gravitational-wave perturbation at any given location in space-time is determined by the distance separating the source and that location. This describes a ...
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1 answer
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Order of magnitude radiation measures conversion?

Standard unit of ionizing radiation dose is Sievert. I can get a rough idea of how dangerous absorbing various amounts is from https://xkcd.com/radiation/ and other sources. There are many other ...
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1 answer
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Why does the universe manifest scale?

I'll try outline my question in clear terms, articulating specific aspects that are its primary motivators. I'm just beginning in my exploration of physics as a student, but a persistent question that ...
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-4 votes
2 answers
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Why do people not have gravitational attraction? [closed]

Gravitational theory says every thing that has mass attract each other. So why don't people attract each other and overlap
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2 answers
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How do you calculate Reynolds and Mach's numbers before solving the Navier-Stokes equations?

Apologies in advance if the question is trivial. I am accustomed to electromagnetics but an amateur on fluid dynamics. My understanding is that the Navier-Stokes equations are solved to determined ...
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1 answer
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Sun's energy and grand unification

According to Wikipedia, The approximate grand unification energy value is equal to $1×10^{25}$ eV or $10^{16}$ GeV This is equal to $1602176$ J. Now, The Earth receives 174 petawatts (PW) ...
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When is the order of magnitude not equal to the exponent of scientific notation?

Explain why the order of magnitude is sometimes not the same as the exponent in scientific notation. It is because of the units?
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1 vote
3 answers
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Where is the line between Quantum and Relativity?

Its often said QM is for the very small and GR for the very large. This brings to mind that there should be some limit at which one starts to apply and the other stops. Now I know there are more ...
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2 votes
1 answer
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Different approch on Order of magnitude confusion [closed]

My problem: How many orders of magnitude larger is the sun $(1.99$ x $10^{30} kg)$ than the moon $(7.32$ x $10^{22} kg)$. Justification 1: So according to my teacher, we can do this question by ...
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3 votes
2 answers
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What is the point of generalizing a more specific result to an order of magnitude?

In my textbook, an example wants me to find an estimate of the number of cells in a human brain. It gives the volume of the brain as $8 \times 10^{-3}\ \rm m^3$ which it then estimates further as $...
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26 votes
4 answers
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If an apple is magnified to the size of the earth, then the atoms in the apple are approximately the size of the original apple

Quoting from the Feynman Lectures on Physics - Vol I: The atoms are 1 or $2 \times 10^{−8}\ \rm cm$ in radius. Now $10^{−8}\ \rm cm$ is called an angstrom (just as another name), so we say they are ...
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-1 votes
1 answer
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What would happen if gamma-ray burst from a supernova burst hit the sun? [closed]

What would happen if gamma-ray burst from a supernova burst hit the sun? Would the sun explode? Would the sun expand. Have a longer lifetime? Shorter Lifetime? Because people are nit-picky about stuff ...
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Why are the Planck charge and Planck mass values so much larger than observed particles? [duplicate]

The Planck charge and mass values seem rather unusual. Is this an indicator that there is a lack of understanding in current theory, or is there a logical explanation for the magnitude of these two ...
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2 votes
1 answer
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How much bigger is $a$ than $b$ when we write $a \gg b$?

When a condition of some physical quantity $a$ and $b$ is presented, say $a \gg b$, how much bigger do we say $a$ has to be than $b$? $10$ times? $1000$ times? $10^6$ times? Some context: I am ...
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2 votes
1 answer
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How much faster is the chain reaction in a power plant than that of natural uranium ore? What about a nuclear bomb?

How much faster does the fissile uranium in a power plant 'break down' than an equivalent amount of naturally decaying U-235? How much faster is the chain reaction in a bomb compared to a power plant?...
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1 answer
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Theory on how to break the speed of light [closed]

I am 14 years old and I think I have a good grasp on physics but I have a question. Imagine you were to shrink everything in the universe (except for yourself) down to the size of an atom and it was ...
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2 votes
2 answers
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Do you create gravitational waves by clapping your hands?

I was thinking that given that GW's can be created by the merger of both black holes and neutron stars I don't see why any two colliding objects wouldn't also be able to create gravitational waves, ...
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Physical reason for light incoherence

In my physics notes it is stated that the light phase changes every 10^-8 seconds, hence light from 2 light original light sources. I understand how light from incoherent light doesn't allow for ...
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1 vote
2 answers
197 views

Confusion about uncertainty principle

A book is lying on the table. It is at rest. Its velocity is 0 and uncertainty in velocity $\Delta v$ is 0. Does this mean that uncertainty in its position is ∞?
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4 votes
2 answers
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Magnitude of Black hole entropy

I was looking with a friend of mine through time travel related stuff, and for some reason we ended up at the Hawking equation for black hole entropy which is: $$S= \frac{\pi Akc^3}{2hG}$$ where: A:...
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how long does it take for a photo-conductor to become a conductor when exposed to light?

How fast does a photo-conductor reach full conductivity when exposed to the appropriate wavelength of light? How fast does it cease to conduct when the radiation ceases? It might vary, so I could also ...
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1 vote
0 answers
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Heating a city with air conditioning units? [closed]

A couple years ago I have estimated that the heat generated by air conditining units is larger than the heat from the sun. So I assumed that there is about 1 kW of solar radiation per m². In the ...
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0 votes
1 answer
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If I have electric current going through a superconductor and cut off the power in what fraction of a second will the electrons stop moving?

If I have electric current going through a superconductor and instantly cut off the power supply(rendering the circuit open, and not at all closed), In what tiny fraction of a second will the flowing ...
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0 votes
1 answer
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Why can't we prepare the moon for colonization by shipping oxygen to its atmosphere?

Why can't we take oxygen to the moon in order to civilize it? We can store oxygen in rockets then take them to moon and release it there. Even if the moon's gravity is weak, it will hold on to the ...
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2 answers
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Order of magnitude (serway 9th) [closed]

In my text book I have following example to present computation of order of magnitude: $$0.008 \space 6\space m \sim 10^{-2}m$$ I dont understand whether I am supposed to multiply $0.008$ with $6$, ...
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1 answer
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What do we mean by order of a parameter?

This questions looks a bit stupid. But I am confused on a statement which says that the value of some xyz parameter is expected to be of order 1. Does it mean that its value is less than $10^1$ or its ...
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6 votes
3 answers
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How many photons enter our eyes per second when looking at the blue sky on a sunny day?

How many photons enter our eyes per second when looking at the blue sky on a sunny day? Say the sun is directly over head and you are looking at the blue sky on the horizon. Say that the pupil is 2mm ...
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1 vote
1 answer
179 views

Ray Optics: Reflection and Refraction

Suppose you have extremely sensitive photographic film and you can expose it in an optical system for a very long time. Will you be able to record a virtual image on film?
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