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Physics : Recent Questions and Answers (Page 727)

Find answers to your questions about Physics or help others by answering their Physics questions.

Query in inner product axioms in QM

In inner product spaces in $mathbb R$ we have an axiom stating that:$$ langle x, xrangle geq 0 text{and} langle x, xrangle...

Asked on 12/19/2020

2 answer

What's the difference between a linear operator and a tensor?

In Quantum Mechanics we mostly use linear operators which often represent a physical observable,In relativity we mostly work with tensors to describe how things change. But both objects are...

Asked on 12/19/2020 by Coderboy

3 answer

Weinberg’s proof of Wigner's theorem

I'm working through the proof of Wigner's theorem in Weinberg's The Quantum Theory of Fields Volume 1 Chapter 2 Appendix A pp. 91. Consider the following steps of the proof...

Asked on 12/18/2020

1 answer

Bath-Scales weight or mass?

I read that bath scales measure body weight and not mass which means they measure m*g and not m.If I got a reading of 50 kg, does that mean that...

Asked on 12/18/2020

2 answer

Do metals have negative permittivity(real part) at microwave frequencies?

I have been studying metamaterials from "ELECTROMAGNETIC METAMATERIALS:TRANSMISSION LINE THEORY AND MICROWAVE APPLICATIONS" by Caloz and Itoh. They have commented that metals at optical frequencies have negative permittivity. My question...

Asked on 12/18/2020

0 answer

What exactly is varied in the left-hand-side of Schwinger's quantum action principle?

Schwinger's quantum action principle states, that if you "vary the field Operators" $$hat{phi'}(x') = hat{phi}(x) + delta hat{phi}(x)$$ (which changes the Action Operator), then "the variation...

Asked on 12/18/2020

1 answer

Seemingly contradictory situation in electrical system loss

In a power supply system, we know that we decrease the current and increase the potential difference. If we decrease the current by a factor of 10 and increase potential...

Asked on 12/18/2020 by Swapnil MZS

2 answer

Centripetal Force Acceleration

In uniform circular motion, acceleration is $frac{v^2}{r}$ and time which it acts $rightarrow 0$. So $Delta v = 0$, but then why/how does direction change, when the...

Asked on 12/18/2020 by user23503

7 answer

Time ordering operator if commutator is $c$-number function

I have a question concerning the time ordering operator. Let's suppose we have a time evolution generated by some Hamiltonian $H(t)$ given by$$U(t)=T_leftarrowexpleft(-mathrm{i}int_0^tmathrm{d}s,H(s)right)tag{1}.$$In Breuer...

Asked on 12/18/2020 by randomdude

2 answer

Does an overcast sky alter the sound waves coming from above it (like the sound of an airplane)?

This morning, in our little backyard, I heard an airplane that was flying above the clouds, which were completely and uniformly covering the blue sky, as if they formed one...

Asked on 12/18/2020

0 answer

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