# Questions tagged [energy]

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 the [energy-conservation] tag if it is specifically about its conservation.

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### Energy stored in the electric field of an electron

Energy stored in the electric field or self energy of a solid sphere of radius $r$ and uniform charge distribution $q$ would be $$\frac{3}{5}\frac{1}{4\pi\epsilon_0}\frac{q^2}{r}$$ This result could ...
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### Relativistic energy and Momentum understanding

After discussing with some people, it appears to me that the way to define quantities like "energy" and "momentum" in general, is to just treat them as "conserved quantities&...
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### Significance of resemblance of Electrical energy with Potential energy of spring

In a spring-mass system the total mechanical energy is represented as: $TE= 1/2kx^2 + 1/2mv^2$ $k$ being the spring constant and $x$ being the displacement. In L.C Oscillations we find the total ...
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### Can average power be non zero, but instantaneous power be zero

Q. A wind-powered generator converts wind energy into electric energy, Assume that the generator converts a fixed fraction of wind energy intercepted by its blades into electrical energy. For wind ...
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### Kinetic energy and work-energy theorem [closed]

I don't understand how this step has done which i have marked so please help me [!]1
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### What qualifies as “Energy” in the Einsteinian sense of the word?

As an absolute beginner to special relativity (and all the 1900s Einstein stuff), I find it hard to grasp the real meaning of the term energy used in the popular equations. I’ve heard it is possible ...
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### Energy conversion of electrons in cathode rays

From the principle of conservation of energy, for each electron: Electrical potential energy = Kinetic energy $$eV = \frac{mv^2}{2}$$ $$v = \sqrt\frac{2eV}{m}$$ where e is the charge of an electron, V ...
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### Does an infinite wire of charge have an infinite potential energy per unit length?

I was doing a physics problem in Purcell's E&M book when I encountered a problem that asked to find the work needed per unit length to assemble an infinite wire charge of radius $a$, by bringing ...