Tagged Questions

Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework questions.

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Entropy with infinite baths

I'm struggling with the following problem: (Stephen J. Blundell, Concepts in Thermal Physics S. 154 Problem 14.5): A block of lead of heat capacity 1kJ/K is cooled from 200K to 100K in two ...
128 views

2D. Force applied at angle to body, where translational vector will be directed?

I'm not a physicist and just making some research by the way of creating simple physics simulator, because of that, sorry if this is very dumb question, but I really need help with it. Let's assume ...
87 views

Super-dense coding protocol with a key

I have this assignment: Show that super-dense coding protocol with the key in the state $\frac{|00⟩⟨00|+|11⟩⟨11|}{2}$ is equivalent (in a sense of transmission rate and security) with ...
403 views

Deriving expression for motional emf

I'm having a trouble deriving the expression for emf caused by the Lorentz forces in a moving conductor. Consider the following classical example of a slidewire generator which consists of U-shaped ...
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Emf of a rod sliding on two conducting rails [closed]

The following is the question. Actually, I do not know how to find the answer. I have tried to find out the solution or hints from the lecture note given to me but it is quite difficult to ...
413 views

Lie derivative of Riemann tensor along killing vector ( = 0 )

I'm currently learning the mathematical framework for General Relativity, and I'm trying to prove that the Lie derivative of the Riemann curvature tensor is zero along a killing vector. With the ...
361 views

Diffraction Grating Spectrometry Question [closed]

Yes, this is a homework question, but I've already failed to solve it enough times that the online system hosting it isn't going to give me any marks, so I figure it's a good time to stop hitting the ...
80 views

A change in the mass of the moon [closed]

Would a change in the mass or radius of the moon have any effect on its speed? When asked this question in an assignment, I stated that it did not. My reasoning being that a change in the mass or ...
256 views

Let's have interaction between gravitational and scalar real fields. For an action of gravitational field in vacuum I add term $S_{m} = \int d^{4}x\sqrt{-g}L_{m}$, where $$L_{m} = \frac{1}{2}g^{\mu ... 1answer 65 views Optics & Law of Cosines I'm supposed to use law of cosines on S_1S_2P in the following diagram that relates to a lens: To arrive at the following equation:$$ \frac{r_2}{r_1} = [1 - 2(\frac{a}{r_1})sin(\theta) + ...
36 views

a mass hangs from three ropes (as shown in the Picture) can someone pleas help me with this?
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Finding possible values of $L_x$ given $L^2$

Here's a homework problem I'm working on. I am not asking for the answer, but any guidance or comments on the approach are appreciated. Given that a measurement of $L^2$ for a free particle has ...
231 views

About partially polarized light and the degree of polariztion

When I was taking Optics course, I found there were several questions about polarization of light. I use the textbook of Hecht. It seems that the definition of degree of polarization may be not so ...
127 views

What happens when you give excess energy to an atom?

So this is my question: An electron in a hydrogen atom in its ground state absorbs energy equal to the ionisation energy of $Li^{2+}$. The wavelength of the emitted electron is? I started off by ...