Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

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Can two different objects or system of molecules have different temperatures, but having same internal kinetic energy?

If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and ...
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Is all energy quantised?

I'm wondering if all energy is quantized.Can a particle with kinetic energy have any value of kinetic energy or is kinetic energy also quantized?My reason for asking this is that if a particle is ...
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What happens to the average kinetic energy if you double the temperature?

I've always wondered what would happen to the average kinetic energy if you double up the absolute temperature of an ideal gas. My hypothesis is that, since the temperature is proportional to the ...
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How is the energy spectrum of a gamma ray in a material?

I'm trying to solve the following problem for a course in radiation physics. A thin ray of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity and the energy of the ...
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How do they find the energy of a photon?

Is the actual energy of a photon ever measured? How is it done? I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ...
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Energy, Power, normalized time-series [on hold]

Given the following (productino of an energy-plant): Total energy production for a year (in Wh) Normalized hourly production ( 0 - 100%): For every hour a value: 100% means full production; 0 % ...
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Calculating engine starter’s energy use

During a discussion on start-and-stop vehicle technology some bloke began pushing the point that re-starting the car uses stored energy from the battery, which needs to be replenished by increased ...
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4answers
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Understanding mathematically the free expansion process of an ideal gas

I'm trying to understand mathematically that for the free expansion of an ideal gas the internal energy $E$ just depends on temperature $T$ and not volume $V$. In the free expansion process the ...
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1answer
122 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
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2answers
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Where does the energy of a lightning strike go?

Lightning contains a lot of energy, so where does this energy go after lightning has hit the ground? Does it travel all the way to the core? What happens after that?
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1answer
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What information does kinetic energy and work give us about a body?

When I studied momentum I learned that momentum says about a body how hard is it to stop it. In addition, I learned that impulse tells us in some way how much time would I need to stop the object. If ...
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What is temperature dependence (Schottky defects)?

The problem requires us to use the following property to determine the temperature dependence: For a system in thermal equilibrium in a heat bath at temperature $T$ the Helmholtz free energy is a ...
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0answers
14 views

Energy losses of a ball, hitting the ground due to elastic and accelerating processes

There is a question about gravitational force and irreversibility. In my answer I pointed towards the phenomenon of photon emission during accelerations and by this of energy loss. My last sentence ...
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2answers
53 views

What was the initial source of energy?

According to law of conservation of energy; "Energy can neither be created nor be destroyed but may change it's form" Where did the energy come from which led to the creation of universe by big bang?
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vibrational motion in gases

In a debate, I argued that vibrational atomic movement as cause of internal energy is prominent in solids (due to their crystal structure) and it is not prominent in gases. I think this also applies ...
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2answers
25 views

Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
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1answer
225 views

What happens to gas molecules after ionization?

I know that gas molecules conduct electricity after they get ionized but what will happen if we keep increasing the voltage even after ionization? Will it explode? If it will then how much energy ...
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1answer
51 views

How do I remove the negative sign from this derivation?

A homework problem required me to show that the first equation below can be written in the form of the second equation. It was all fairly simple except for the negative sign. I'm not sure how this is ...
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1answer
19 views

0.19 kg apple falling (a problem on Work and Power) [on hold]

Problem A 0.19-kg apple falls from a branch 3.5 m above the ground. a) Does the power delivered to the apple by gravity increase, decrease, or stay the same during the time the apple falls to the ...
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1answer
612 views

Energy dispersion in graphene

Given that graphene has linear energy dispersion near the Fermi level and the dispersion is given by $E=\hbar \nu_F|\vec{K}|$, I would like to determine the density of states. I think it is equal to ...
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0answers
24 views

Specific Heat capacity [on hold]

The total heat capacity of a caloriemeter, heater, stirrer is 107 joules per kelvin. Mass of the liquid in caloriemeter is 0.241 kg. The power supplied by heater is 41.48 watts. The initial rate of ...
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1answer
39 views

How does parallel plate lose energy when deflecting charged particles

Say you have a parallel plate setup, each plate is charged with ±Q of charge, and is then disconnected from the power source and is insulated from the environment. There is no way the plates can be ...
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2answers
120 views

How does voltage divided by EMF show efficiency?

I get that electromotoric force (emf) is energy per coulomb supplied and that voltage is energy per coulomb used but I don't get what it means when we say that the voltage divided by the emf gives the ...
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Why can't we destroy energy?

From a wikipedia article: In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither ...
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1answer
23 views

How is there GPE in objects that are on top of a hill?

What I don't understand about gravitational potential energy is that objects have the greatest GPE on top of a hill and it decreases as they go down the hill. At the top of the hill, they are on the ...
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3answers
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What are high energy photons?

I have often read the term High Energy photons, does this mean that there do exist photons with low energy? Aren't they supposed to have constant energy according to $E= h\nu$?
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1answer
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Energy of electromagnetic wave

Its given here that energy density of an electromagnetic wave is $$\vec S=\frac{1}{\mu}(\vec E\times\vec B)$$ How is the above expression derived? And when did energy become a vector? I though work ...
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1answer
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Where are the electron exchanges happening in solar cell physics when considering the photon?

When considering solar panel physics, are we taking an electron from Light(photon), or is the energy of Light causing an electron to jump in said solar cells through excitation? Is the photon even ...
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1answer
40 views

Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
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1answer
39 views

Can the internal energy of an ideal gas system increase as temperature decreases?

If $\Delta U = Q + W $ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the colder gas ...
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1answer
182 views

How do I describe and calculate the effect of an impacting object?

My lab studies the physiology of impact injury on biological tissues. I use a pneumatic cylinder to impart injury into a biological sample and then assess the molecular and physiological changes in ...
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0answers
25 views

How would you calculate consecutive bounces on a trampoline to find how much energy is lost each time or what percentage is lost each time? [on hold]

How would you calculate consecutive bounces on a trampoline to find how much energy is lost each time or what percentage is lost each time?
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0answers
30 views

Calculating the data rate for a baud signal [closed]

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
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1answer
2k views

Can sound produce electricity?

Energies of wind and water can produce electricity. But, can sound energy also be used to produce electricity?
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Example of law of conservation of energy

Law of conservation of energy states that "Energy of the universe remains constant. Energy can neither be created nor be destroyed, but it can be transformed from one form to another". So I ...
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is the potential energy of a black hole infinity

It appears like black holes posses an escape velocity greater than the velocity of light. It takes an atom infinity energy to travel at speed of light.Do black holes posses that energy to retain ...
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0answers
41 views

Can the linear momentum of a system be constant, even though its centre accelerates?

My instructor says if the velocity of center or mass is constant, it means that the linear momentum of a body is conserved. So if no external force acts on a body, there is no change in the linear ...
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2answers
247 views

Will an object with a higher temperature lose its heat faster than a cooler, yet warm object

I'm after the math, which I don't understand yet and can't find elsewhere. The variables are: Two identical cups, A and B The same volume of fluid is contained in each cup, test fluid is water. ...
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1answer
199 views

Physical interpretation of distances

Suppose we have a universe with only two distinguishable particles, neglecting gravitation. These particles start off next to each-other, ostensibly "touching" each-other and at rest. If it takes ...
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1answer
26 views

“Carbon capture into fuel” - where does the energy come from?

I recently found an article titled "Scientists find a way to convert Carbon Dioxide from air into fuel" (here), and my immediate reaction was "surely not - the energy balance would kill you right ...
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1answer
33 views

Why am I not shocked when I touch a tree, and the tree touches a power line? [closed]

Why am I not shocked when I touch a tree, and the tree touches a power line?
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1answer
109 views
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1answer
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How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel ...
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If a system has an internal energy equal to 0, does this mean it doesn't exist?

Enthalpy is a measure of energy in a thermodynamic system: It includes the internal energy, which is the energy required to create > a system, and the amount of energy required to make room for it ...
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3answers
643 views

Why is salt so hard to remove from water?

Water molecules and various salt molecules are very different. However, it seems very difficult to separate the two. Once a salt is dissolved in water, an energy or chemical intensive method (like ...
6
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1answer
39 views

If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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2answers
143 views

Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...