In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.
Hey all, am new here so please go easy on me.
This regards observation of Markarian 501 with the MAGIC telescope. Gamma rays appear 4 minutes after the visible light. That high energy photons (gamma rays) travel more slowly through the "quantum foam" has been suggested, and even more mundane...
Howdy,
Can anyone explain qualitatively (without using any maths) why a particle with a smaller mass has a greater probability of tunneling through a potential barrier than another particle with a larger mass but of the same total energy?
Thanks
Homework Statement
Suppose that a particle of mass m is confined to move in the x-y plane in a 2-dimensional box of length Lx = L and LY = ½ L. Calculate the energies of the six lowest states.
Homework Equations
not sure to set up this problem?
The Attempt at a Solution
the most...
Homework Statement
Problem 9. Evaluate the matrix elements \langle n + \nu|x^2|n\rangle and \langle n + \nu|p^2|n\rangle in
the harmonic oscillator basis, for \nu = 1, 2, 3, 4 :
1. Using the closure property and the matrix elements.
2. Applying the operators x^22 and p^2 , expressed in...
If a diatomic molecule's vibrational energy is increased to the dissociation energy of that molecule, will that cause the molecule to rip itself apart? Is it the change in vibrational energy that causes the molecule to dissociate?
Hi,
Considering a pn-junction at thermal equilibrium, why does following count
EFp=EFn-eVd=EF,
where EFp and EFn are the quasi-Fermi energies in the neutral p- and n-type regions before equilibrium is established, with EFn>EFp, EF is the Fermi energy after equilibrium is established...
Homework Statement
What multiple of the energy needed to escape from Earth gives the energy needed to escape from (a) the Moon and (b) Jupiter? Use the Table (link below) if necessary
http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c13/fig13-19.gif
Homework Equations...
I have a question which may seem stupid, but I think I missing something here.
I see 2 equations describing allowed energies for electrons in hydrogenic atoms, being:
E = -\frac{hcRZ^2}{n^2}
And
E = -\frac{RZ^2}{n^2}
I assume that both are correct, but what makes the difference? Is it the...
Homework Statement
A stationary uranium-238 nucleus undergoes alpha-decay. What is the ratio of the daughter nucleus to that of the alpha-particle?
P.S. It's a practice problem for which I had the final answer, but I'm not sure how to reach it.
Homework Equations
I guess it's based on...
if i calculate the change in binding energy in a decay process such as B-decay using SEMF, and then i calculate the same difference in binding energy using the difference in atomic masses and electron masses. why are they different?
Homework Statement
A meson (elementary particle) decays into two photons, each of energy 150MeV in its rest frame. Find the mesonic kinetic energy in the case of a symmetric decay in flight with an angle of 60degrees between the photon momenta (30 degrees for each particle on each side of the...
Question about internal energies... PLEASE HELP ME!
What must be true for two objects of the same material to have the same internal energies?
(Choose all that apply)
a. The masses of both objects must be equal
b. Both objects must have the same density
c. The temperatures of both...
I am an A-level teacher so I don't want an answer in terms of anything too complicated (for my students!)
The hydrogen atom has a ground state energy of -13.6eV. I am happy with this.
This means that the electron needs 13.6eV of kinetic energy in order to become free of the nucleus...
Career in alternative energies engineering...
I have a BS in Mechanical Enineering with several years experience with general ME practices (i.e CAD design of parts and systems, CAM and machine work, project management). I am looking to start a carrer in alternative energy engineering. I am not...
Homework Statement
Initially, a 10 kg block is sliding along the floor at a speed of 5 m/x. The coefficient of friction between the block and the floor is 0.5.
What are the KE, PE and total energies of the block after sliding 2.0 m?
What is the block's speed after sliding 2.0 m?
I...
The succesive ionization energies in kj/mol of an element x found in period 3 of the periodic table are: 1800,3000,3600,5800,13200. With the aid of a periodic table,what is element x?
What do the phenomenologists of unified theories (strings, loops etc) try to match at lower energies when there are so many conflicting theories lying around at these energies?
I understand that certain things should be there in any model - like chiral matter, three generations etc - but a lot...
just a question about the energies associted wuth the schrodinger equation> are the energy values always positive values. I thought that since when the eigenfunctions exist the particle is in a bound state, that the energy should be less than that required to escape a bound state and should be...
I have to find the kenetic energy lost in the problem. I have both initial and final kenetic energy, how do i calculate the percent loss? I tried final over initial times 100 but that is not correct.
This question is not a homework question. I am having a little trouble with the ionization
energy graph. I understand that the noble gasses are the most stable
and hence require the most energy to be ionised, but why is it that after you
add even number of electrons the ionization energy...
Homework Statement
So the question asks me to find the energies of the 2nd, 3rd, 4th, and 5th excited states in a three dimensional cubical box and to state which are degenerate.
Homework Equations
-\frac{\hbar^{2}}{2m}\nabla^{2}\Psi + V\Psi = E\Psi
The Attempt at a Solution
so I...
Homework Statement
A hydrogen atom is in the n=6 state.
a) Counting all possible paths, how many different photon energies can be emitted if the atom ends up in the ground state?
b) Suppose only\Deltan=1 transitions were allowed. How many different photon energies would be emitted...
Homework Statement
What is the calculated binding energy of the electron in the ground state of (a) deuterium, (b) He^{+} and (c) Be^{+++}?
Homework Equations
For the hydrogen atom, E_{n} = - E_{o} / n^{2}
E_{o} = me^{4} / 2hbar^2(4\piEo)^2
The Attempt at a Solution
Not sure...
Homework Statement
A simple pendulum has a length equal to 0.6 m and has a bob that has a mass equal to 0.5 kg. The energy of this oscillator is quantized, and the allowed values of energy are given by En = (n + 1/2)hf0, where n is an integer and f0 is the frequency of the pendulum. Find n...
Homework Statement
I got ask the following question, and i don't know the answer.
Why in a rdioactive decay of 232Th by alpha emission, the alpha particle can have energy 4.01 Mev and 3.95 Mev?
Homework Equations
The Attempt at a Solution
I look up this website and i found...
Hi, first time poster.
Quick question:
Why is the bond energy for a bond that contains a more highly substituted (tertiary) carbon weaker than the bond energy of a bond that contains a less substituted (primary) carbon?
Let me clarify with an example. Say Bond A is a single bond between a...
Hi guys... I have a small question on potential energies:
I have got two potential energies:
\begin{equation}
U_1=-\frac{k^2}{2}+\frac{w\sqrt{3}}{2}\sin^2\theta \cos 2 \phi
\end{equation}
and
\begin{equation}
U_2==-\frac{k^2}{2}+\frac{w\sqrt{3}}{2}\sin^2\theta \sin 2 \phi...
Homework Statement
i) Explain why in alpha decay short half lives correspond to large disintegration energies.
ii) Determine the energy release during the alpha decay of 238U to 234Th. The mass of 238U is 238.0508mu, the mass of 234Th is 234.0436mu, and the mass of 4He is 4.0026mu...
Homework Statement
a wrecking ball, with a mass of 315kg, hangs from a crane on 10.0m of cable. if the crane swings the wrecking ball so that the angle that the cable makes with the vertical is 30', what is the potential energy of the wrecking ball in relation to its lowest position?
What will...
Not sure if this should go here or in the relativity forum... let me know if I need to move it.
I was reading something, and it said this:
"A photon also has a rest mass, which is zero, even though a photon is always moving at the speed of light, and so is never at rest. But if an observer...
Where in quantum field theory does it say that probing something at high energies is equivalent to probing it at small distances? Most of the time things are done in momentum space (such as the Feynman rules) so we have no clue about distances and location.
The only time I even remember using...
Homework Statement
Prepare a table of spectral lines by color, with correct wavelengths, and corresponding energies for every line spectrum you observed. Pick one line spectrum and explain the order of color from least to most energeticHomework Equations
I'm not quite sure what to do here. I...
I have to graph changes in energies. And I have a question - so I have a battery that supplies power to a motor and some sensors. I have to assume it starts with 36000J of energy (chemical energy, right?). Then, pretend a motor uses 22J and shuts off. Now I would have 35978J of chemical left...
Hello, I'd like to ask a question about the electron binding energies of oxygen atom. As is known, when an oxygen atom gains one additional electron to form an anion with charge -1 it gives some 1.4ev, while it gives nearly 7.8ev if two additional electrons are bound to it. Considering that the...
Homework Statement
Suppose that a positron traveling at a speed of 0.93c collides head on with an electron traveling at the same speed.
What is the sum of the energies of the two photons?
Homework Equations
mass of an electron = 9e-31 kg
E=\gammamc2 - mc2
The Attempt at a...
1. The problem statement, all variables and given known data
Hi all.
Lets I have a system, whose Hamiltonian is given by H = p_1 + p_2, where pi is the momentum of i, where this i can be whatever, e.g. momentum in some particular direction. When the Hamiltonian is given on this form, do I know...
Homework Statement
The masses of the javelin, discus, and shot are 1.0 kg, 2.0 kg, and 8.0 kg, respectively, and record throws in the
corresponding track events are about 98 m, 75 m, and 25 m, respectively. Neglecting air resistance,
(a) calculate the minimum initial kinetic energies...
Homework Statement
Consider the box potential
V (x) = 0 0 < x < a
1 elsewhere
a) Estimate the energies of the ground state as well as those of the First and second
excited states for
i) an electron enclosed in a box of size a = 10E-10 m. Express your answer in...
Homework Statement
Two bullets have masses of 4.7 g and 11 g, respectively. Each is fired with a speed of 39.0 m/s.
a) What is the kinetic energy of the first bullet? Answer in units of J.
b) What is the kinetic energy of the second bullet? Answer in units of J.
c) What is the ratio K2/K1 of...
Homework Statement
What are the energies of the ground state and the first two excited states of the He+ ion?
Homework Equations
En= - Eo/n2
The Attempt at a Solution
n=1 for this problem (since there is only 1 electron) so the ground state would have the electron...
Compton scattering and the energies of incident and scattered photons...?
[b]Hey guys! I'm alittle stuck...Hope you can shed light on this for me!
The question is: 'In a head-on compton encounter, the total energy (i.e the rest mass plus the kinetic energy) of the scattered electron is...
So I was doing physics homework today, and wound up spending a couple hours on wikipedia, browsing through topics far out of my league- particularly nuclear physics. I'm left with an aching question that I hope someone here can help me out with.
In a nuclear reaction that requires a certain...
Hi guys,
I hope you can give me any idea about:
After a long molecular dynamic simulation of a polymer under periodic boundary conditions, dihedral and total energies are lower than zero, (negative). do you know the physical meaning of that result?
thanks for reading and for your help...
I'm reconsidering the problem of resonance states.
We know that the resonances in QM are described as the complex energy poles in the scattering amplitude. In the version of QFT, the resonances are described by the complex mass poles of the scattering matrix.
In QFT, I can understand that...
i have two questions...
does an electron have a continuous range of energies? I think the answer is no. am i right?
and also... what does the solution of the schrodinger's equation provide?
"Consider an infinitely sharp pin of mass M and height H perfectly balanced on its tip. Assume that the mass of the pin is all at the ball on the top of the pin. Classically, we expect the pin to remain in this state forever. Quantum mechanics, however, predicts that the pin will fall over...
Homework Statement
A photon of initial energy .1 MeV undergoes Compton scattering at an angle of 60degrees.
Find:
The energy of the scattered photon
The recoil energy of the electron
the recoil angle of the electronHomework Equations
\Delta\lambda= (h/mc)(1-cos\theta)The Attempt at a Solution
I cannot see how the two can be mutually inclusive. If you super impose particles with potential energies that fall off as 1/r that are homogeneously distributed through space then take the gradient of them, I hardly believe that they will result in the exactly the same thing than if you take...