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Absorption spectrum of white light of the Sun

so how does that light still appear 'white', although some of its constituents are missing? (bold mine) It is called perception of color and is tied to biophysics and complicated plots. Note that ...
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2 votes

Absorption spectrum of white light of the Sun

If sunlight is "white", then it is white by definition. A simple glance at the solar spectrum shows that it is neither flat (which would be one definition of a "white" spectrum), ...
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Absorption spectrum of white light of the Sun

As the other folks have said, the absorption lines are quite narrow and the total "amount" of light absorbed is small. But we could actually expand your question. The spectrum of light ...
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1 vote

Absorption spectrum of white light of the Sun

The absorption lines (where constituents of the hot gas surrounding the sun absorb certain wavelengths of the sun's spectral output) are 1) narrow, so in absolute terms not much of the sun's light ...
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2 votes

Why does a spring have potential energy compared to a rod?

In practice there is no such thing as a perfectly rigid rod. All rods compress to some extent, so they are like extremely stiff springs, but they are such stiff springs that you can ignore the ...
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What is the correct derivation of energy stored in parallel plates capacitor?

I'm not sure what you are saying, but the two derivations are equivalent with respect to the the total work required (total potential energy). In the first derivation the work per unit charge must be ...
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What is the correct derivation of energy stored in parallel plates capacitor?

You know that the electric field is conservative, so moving charges from infinity into two parallel plates separated by a given distance should require the same energy regardless of how you move the ...
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2 votes
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Physical interpretation of negative total energy

The total energy can be negative because, away from infinity, the potential can be negative. If the total energy is negative, then regions with zero potential are unaccessible for the particle, since ...
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1 vote
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Explaining internal energy from a macroscopic perspective

What you need really is a proper starter-course in thermodynamics, with a good textbook (and reader can guess which one I recommend!) The logic goes as follows. Various experiments (especially those ...
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1 vote

Explaining internal energy from a macroscopic perspective

The concept of internal energy is introduced in the first law of thermodynamics, based on Joule's work. Based on his experiments with heating and mixing water with a paddle wheel, he realized the ...
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Mass-energy equivalence and gravitational potential energy

When one mass is at some distance from another, we may say there is gravitational potential energy in the system. But where is this energy physically located? It is not inside one mass or the other. ...
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1 vote

Mass-energy equivalence and gravitational potential energy

An object doesn't increase mass when its energy increases. The rest mass is the rest mass. Even with kinetic energy. If an object is moving, its mass doesn't increase. You can associate a mass to the ...
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1 vote

Mass-energy equivalence and gravitational potential energy

In the view of general relativity, gravity in reality does not have any form of well-defined potential that can be considered "energy" in the same sense as the components of the stress-...
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Mass-energy equivalence and gravitational potential energy

Well, I would say object has less mass when at lower altitude. As an example, it's easier to accelerate two boulders when they are close to each other. I mean accelerate to the same direction. If ...
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4 votes

How is energy "stored in an electric field"?

The stress-energy tensor At every point in space there is a density: Build a sphere (or any shape) of gravity sensors and measure the net acceleration into the sphere (technically the surface integral ...
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2 votes

Explaining internal energy from a macroscopic perspective

The Joule historic experience measuring carefully how mechanical work can raise the temperature of water is the basic idea of internal energy in my opinion. We know from mechanics that the work of the ...
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3 votes

How is energy "stored in an electric field"?

If you look at our equations for energy, you will see that they typically settle into two major categories: Energy associated with intrinsic properties of a "thing" Energy associated with ...
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Explaining internal energy from a macroscopic perspective

What came up in comments to this answer to the question quoted in the OP, is that one has to distinguish, on the one hand, phenomenological vs. microscopic models/theories and on the other hand, ...
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-1 votes

How is energy "stored in an electric field"?

The energy is not really anywhere. It's like saying where is the momentum? it's not something you can see or touch; it just happens to be a conserved quantity that is useful. There are many gimmicks ...
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1 vote

How is energy "stored in an electric field"?

If we transfer one small $dq$ charge from one capacitor plate to other, then we need to do some work. Repeat the process like this again and again; this leaves a net negative charge on the first plate ...
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Why energy bands are flat at the edges of the 1BZ?

This is due to Bragg reflection at the zone boundary. I'll stick to a 1D treatment for simplicity in my answer We know that the potential is periodic, i.e. \begin{equation} V(x) = V(x + a) \end{...
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5 votes

How is energy "stored in an electric field"?

Very incorrect and oversimplified but somehow intuitive: Nature tries to "equalize" many "things". For example temperature. Water in every place within a bucket will eventually be ...
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Change in kinetic energy when force is perpendicular to velocity

It is said that when force is applied perpendicular to velocity, there is no change in kinetic energy since there is no change in speed. Exactly what happens when there is uniform circular motion. ...
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12 votes
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How is energy "stored in an electric field"?

What "is" an electric field? One way to look at the world is to see it as a cellular automaton; something resembling Conway's game of life. Of course it's not so simple — the playing field ...
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2 votes
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Change in kinetic energy when force is perpendicular to velocity

The perpendicular component of a force will never change the speed. This is true. What is happening in your case is at the instant that the force along the y-axis is applied, it will, for that short, ...
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-1 votes

What would "break" in reality if I had a perpetual motion device?

If you could have devices having 100% or even more than 100% energy efficiency , then you can easily break the first as well as second law of thermodynamics and cool your ice-cream while sitting ...
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Combustion test of gases for boiler use

Usually people use mass flow controllers, sometimes it is also useful to use a pressure controller. Basically you have cylinders for the gasses you want to mix, at the outlet of the cylinders you ...
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34 votes

How is energy "stored in an electric field"?

This question is deeper than you might expect. Neither energy nor an electric field is exactly what you might expect. First, physics is a description of the behavior of the universe. It is not the ...
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18 votes

How is energy "stored in an electric field"?

The idea is that all energy, including kinetic energy and EM energy (such as that stored in the capacitor) is localized in space, i.e. given any region of space, one can assign net energy to it, and ...
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13 votes

How is energy "stored in an electric field"?

It's a model, created to capture what is seen in experiments. If we attribute the energy of an electromagnetic interaction to the fields, we get the right answer. We don't have an alternative that ...
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Is there an official name for "Lorentz Pairs" like energy and momentum?

What you might be looking for is the concept of Lorentz covariance. A Lorentz covariant quantity is a (finite collection of) quantities which are taken to linear combinations of themselves under ...
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2 votes

Why I cannot write the time evolution operator $e^{-i(T+V)t}$ as the product of operators $e^{-iTt}e^{-iVt}$

When we put the Hamiltonian $H$ in an exponential like this, we are not assuming the $H$ represents a scalar value. The exponential notation used in this case is just shorthand for the Taylor series ...
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May the chemical energy of combustion be wholly released as photon only?

Normally when a molecule gets oxidized, besides electrons moving about (producing some electromagnetic waves) the main effect is that the involved molecules change shape/type. This typically involves ...
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7 votes

Why I cannot write the time evolution operator $e^{-i(T+V)t}$ as the product of operators $e^{-iTt}e^{-iVt}$

Let $t$ be a dummy variable to keep track of orders in a series expansion: $$e^{tA} e^{tB} = \Big(1 + tA + \frac{1}{2} A^2 t^2 + \mathcal{O}\left(t^3\right) \Big) \Big(1 + tB + \frac{1}{2} B^2 t^2 + \...
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1 vote

May the chemical energy of combustion be wholly released as photon only?

Chemical reactions that directly emit photons do exist, see Chemiluminescence or search for "chemically pumped lasers". Note that these generally release heat as well. In order to implement ...
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15 votes
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Why I cannot write the time evolution operator $e^{-i(T+V)t}$ as the product of operators $e^{-iTt}e^{-iVt}$

This is because of the BCH formula $$\begin{align}e^Z~=~&e^Xe^Y \cr\Downarrow~&\cr Z~=~&X+Y+\frac{1}{2}[X,Y]+{\cal O}(X^2Y,XY^2),\end{align}$$ or equivalently, the Zassenhaus formula. But ...
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Initial velocity of a body when the distance travelled by it in the last second before reaching its maximum height is $5\ \textrm{m}$

We know $$S=ut+\frac{1}{2}at^2$$ Substitute $S=h$, $t=t_{f}$ $$h=ut_{f}+\frac{1}{2}at_{f}^2$$ Use the quadratic formula, to solve for t setting the discriminant to be zero, since because this is the ...
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1 vote
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Initial velocity of a body when the distance travelled by it in the last second before reaching its maximum height is $5\ \textrm{m}$

The question has either an infinite number of answers, or no answer. It's convenient to follow the motion for the one second AFTER the ball reaches the peak of its trajectory. (Or run time backwards ...
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1 vote

Initial velocity of a body when the distance travelled by it in the last second before reaching its maximum height is $5\ \textrm{m}$

Assume that the velocity of the body right before the last second starts is V. It decreases to zero in 1s with an acceleration of g, about $10m/s^2$. So, V must be 10 m/s. Alo, the time to drop from ...
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What creates motion at microscopic level?

In the quantum realm there is no "motion" in the same sense as in classical mechanics. A wavefunction can never be in a position eigenstate, so its position will always have a non-zero ...
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2 votes
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Can a magnet repel a ferromagnetic sphere?

A ferromagnetic object in a non-uniform magnetic field will always feel a force in the direction of increasing magnetic field. If you want it to feel a force in the opposite direction then you will ...
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What creates motion at microscopic level?

Question: What creates motion at microscopic level (instead of sending any external force/ perturbation like heat or light)? What creates motion at the macroscopic level? According to the first law ...
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Initial velocity of a body when the distance travelled by it in the last second before reaching its maximum height is $5\ \textrm{m}$

Supposing the ball is thrown up vertically (otherwise the answer is undefined because the problem has not been given enought parameters): Acceleration along $z$ is $a=-g=\ddot z$ where $g\approx 9.806$...
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1 vote

The Hamiltonian of a system under only the effect of an electric field

This answer is meant to address your comment to Roger Vadim's answer (which is clear and correct). Newton's 2nd law for a charge in a uniform electric field says that \begin{align} q \mathbf{E} = m \...
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1 vote
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The Hamiltonian of a system under only the effect of an electric field

The question is unrelated to quantum mechanics, and even to classical mechanics (dealing with Lagrangians and Hamiltonians), but rather to the basic Newtonian mechanics: Indeed, when a particle is ...
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Unit of measurements of energy of particles

The unit of measurement for the energy is $eV$ (electron-volts). Its interpretation is simple: it's the total amount of energy that a particle of charge equal to the measure of the electron charge ...
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Deriving Work-Kinetic Energy Theorem

We start with the definition of work: $$W = \int_{x_{i}}^{x_{f}} F\cdot dx$$ From Newton's second law: $$W = \int_{x_{i}}^{x_{f}} m\frac{dv}{dt}\cdot dx$$ $$W = \int_{t_{i}}^{t_{f}} m\frac{dv}{dt}\...
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1 vote

Deriving Work-Kinetic Energy Theorem

$$\begin{aligned} W_{\text{ext}} &= \int_{x_i}^{x_f} \sum F \ dx \\ &= \int_{x_i}^{x_f} ma \ dx \\ &= \int_{x_i}^{x_f} m \frac{dv}{dt} \ dx \end{aligned}$$ From this point, we note that $x ...
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Deriving Work-Kinetic Energy Theorem

You have overcomplicated your derivation by trying to derive within the integral. Start with the differential forms first then integrate at the end $$W = Fdx$$ $$W = m \frac{dv}{dt} dx$$ $$W = m \frac ...
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