# Tag Info

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Sure, this definition is useful for any kind of cyclic phenomenon, why not? Think for example of 'phases of the moon'. In the case of fourier analysis however, 'phase' usually means: phase of a sinusoidal component, not the phase of the waveform that is being analyzed.

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All of this is all right, but the problem is that I'm taking a course on electrodynamics and the teacher said that the work $W_{\mathrm{ext}}$ done by one force external to the system is $$W_{\mathrm{ext}} = \Delta K + \Delta U,$$ that is the change in the total energy of the system. I don't know where this comes from It follows from the work-energy ...

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the fermi energy is such that all states with a energy same or lower are occupied at zero temperature. You have gaps in the spectrum leading to a wider range of "possible" fermi levels. Take the first case (assuming e_3>e_2=e_1): at zero temperature the states e_1 and e_2 are occupied and e_3 is not. Meaning e_f must not be smaller than e_1,e_2 and must be ...

1

Probability is the chances of occurrence of an event, say for example the event is to find an electron around the nucleus of an atom. If the atom has an electron around the nucleus then the probability of finding the electron around the nucleus is one(1). but if the electron is to be sort some place away from the vicinity of the nucleus then the probability ...

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According to here, there was no precise definition before this group redefined what it meant for a group of galaxies to constitute a supercluster--before their redefinition, it seems it was just loosely defined as "extended regions with a high concentration of galaxies." They now define a supercluster to be a volume in which "the motions of galaxies are ...

2

From the Wikipedia article "Escape velocity": Defined a little more formally, "escape velocity" is the initial speed required to go from an initial point in a gravitational potential field to infinity with a residual velocity of zero, with all speeds and velocities measured with respect to the field. Additionally, the escape velocity at a ...

1

It would be perfectly possible to reach a distance from the Earth where the sum of an object's (space ship) kinetic energy and its gravitational potential energy is equal or larger to zero, with a continuously powered (thrusted) vehicle, as long as during flight the vehicle’s thrust always overcomes the gravitational attraction exerted by the Earth. But for ...

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The earth is at the bottom of a gravity well. The amount of kinetic energy you need to escape that well depends on how far down you are in it. At the surface of the earth, or rather in low earth orbit above the atmosphere, escape velocity is about 25,000 mph. That means if the rocket accelerates to that speed, it will go up out of the well, and eventually ...

3

Yes, it's an initial velocity in a ballistic trajectory in a vacuum. The escape velocity is derived using conservation of energy at two different points in time, as $\frac {1}{2} mv_0^2-\frac {G M m}{r_0}>0$. $v_0$ means initial velocity. In practice you haveto worry about the atmosphere and all that.

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The Fermi energy, $\epsilon_F$, is only equal to the chemical potential, $\mu$, when the Fermi gas is at zero temperature. The Fermi energy basically means, "chemical potential at zero temperature". At any other temperature you could find $\mu$ via one of the standard thermodynamic relations (i.e. as the appropriate derivative of a free energy).

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Jean Bouridan, rector of the University of Paris around 1350, was the first philosopher, to my knowledge, who specifically stated the current concept of momentum. He said that impetus was proportional to the product of weight and speed. Momentum is considered to be the product of mass and velocity (velocity has direction as well as magnitude). Momentum is ...

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You've got it a little backwards - physicists first defined the quantity $m \cdot v$ because it quantified the amount of "motion" an object possessed. They named it "momentum". Modern physics is primarily concerned with the quantity $m \cdot v$ (and the updated versions of that quantity in more recent frameworks of physics) because it is conserved. This ...

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The main purpose of microscopy is to observe things that cannot be or are hardly observed by naked eye. To justify the purpose one can utilize everything that suits the purpose. For example, it can be different light paths coming from different parts of a sample or different reflection from different parts of a sample etc. Or in terms of AFM it can be ...

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