# All Questions

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11 views

### A Hotwheels Problem

I have a Hotwheels track set. It has a looped structure such that at some point in the car's trajectory, it becomes upside down. But in such a situation, it doesn't fall to the ground. I understand ...
33 views

### Measuring the energy of a photon with E = mc²

Clearly light has energy because the photoelectric effect or photosynthesis would not work. The formula E = mc² doesn’t work for measuring the lone energy of light as a massless particle, but it works ...
234 views

### What happens if I send light from two light sources through a single slit?

I have two identical point light sources A & B emitting the same frequency. They are equidistant from the single slit and from the line passing perpendicularly through the middle of the slit ...
56 views

### Are black holes 4-dimensional balls of spacetime? If so, will they have 3-sphere surfaces?

If black holes are 4-dimensional balls of spacetime, they will have a 3-sphere surface with a 3-dimensional volume. Would this allow infalling matter to remain within this surface?
29 views

### Determining Whether a Collision is Elastic or Inelastic

I am having a lot of trouble with this problem. The answer key says that the collision is inelastic, but I am not sure how they came to this conclusion given that there is no indication of whether ...
159 views
+50

### What is the meaning of $\vec H$ with respect to the total field?

Now before saying anything, I have seen the similar questions in this page regarding $\vec H$ but no one has fully convinced me yet, since I will try to give another perspective to this question. We ...
5 views

### How,in induction of electric charges, the field developed due to separation of charges exactly cancels out the external field?

I have been learning electrostatics, and I didn't quite understand why charges reside only on the surface. The charges are moved until they reach the surface after which they cannot move further and ...
8 views

### Predicting atomic dipole transition properties (reference request?)

At the moment, I'm interested in the question of how to predict the strengths of atomic transition dipole elements for atomic transitions. A quantum 101 approach to solving this problem involves ...
2k views

### Sun light collimation

Is it possible to make sun light collimated in such a way, to increase energy density and keep it more less parallel? like on the Earth we have intensity of sun approximately 1300 watt/m2. If we use ...
1 vote
16 views

### Conflicting lensmaker's equation representation

I keep finding these two conflicting forms of the lensmaker's equation. I understand that (n2-n1)/n1 is the same as (n-1) if referring to a lens in air, but I can not make sense of why the reciprical ...
1 vote
16 views

### Transformation rules for components of tensor fields

In general relativity, when asked to prove that an object is (resp. is not) a tensor, we are often expected to show that its components follow (resp. don’t follow) the so-called tensor transformation ...
28 views

### Ejected bodies, dynamical friction and dark energy?

I have a question after reading a couple of papers (https://arxiv.org/abs/1707.06220 and https://www.arxiv-vanity.com/papers/1102.0007/). Here, the authors seem to indicate that when bodies like stars ...
1 vote
338 views

### Transformation of states and operators under Quantum Lorentz Transformation

For any Homogenous Proper Orthochronous Lorentz Transformation $$x\to\Lambda x$$ , there is a unitary linear operator $$U(\Lambda)$$ [Bogoliubov(1980),Srednicki(2007),Weinberg(1995)] which can be ...
13 views

### Buckling Question from Hibbler Textbook

Hello! I have a question from the Hibbler Textbook on Mechanics of Materials! The exact statement of the problem reads: "A W150 * 24 steel column is 8 m long and is fixed at its ends as shown in ...
22 views

### When do pairs of quarks form jets vs mesons?

For certain processes with low momentum transfer, such as the Kaon decay shown below, quarks will form bound states of mesons. Whereas for higher momentum-transfer processes, such as the decay of an ...
40 views

39 views

### Circuits: Determining the voltmeter in physics [closed]

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193 views

### Why Curie temperature is bigger for smaller lattice in 2D Ising model

Using Metropolis algorithm, Curie temperature was calculated for square lattices with different sizes 4x4, 8x8, 16x16 and 32x32. Here Curie temperature was estimated as temperature of maximum of heat ...
47 views

### Why temporal and spatial term is multiplied to get the wave equation?

When deriving the wave equation we have: $$y_{spatial} = A\exp(ikx)$$ $$y_{temporal} = A\exp(-i\omega t).$$ Then the overall wave equation is obtained by multiplying both time and spatial component. ...
201 views

### What does elasticity with torque and twist depending on normal strain and normal stress look like?

A twisted rope has a relation between normal stress, along the rope, and twist of the rope. If a rope is twisted more it becomes shorter. If it is untwisted it becomes longer. Likewise for coils and ...