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# Physics : Recent Questions and Answers

## Where are the electrons of a cathode ray tube coming from when using AC?

I see in this picture a beam of electrons leaving the cathode. But I read before, that the electrons can flow out of a copper wire only, if they are...

## Is it resistance of filament or current thorugh it which determines brightness of bulb?

SO brightness of bulb. Does it depend on the resistance or current in it?I have two bulbs keeping everything same except resistance. So Bulb A - high resistance Bulb...

## Shouldn't $CO_2$ forcing depend on the surface temperature?

When I read about radiative forcing due to CO2 it says:"Radiative forcing is a measure of the influence a factor has in altering the balance...

## If the fictitious forces (ex: centrifugal) help the observer feel stationary, why does the person feel a force in the opposite direction?

I searched and viewed similar questions on here but still am very confused. Is it because of the observer's inertia? If so, shouldn't we feel a 'push' towards the point...

## Confusion with redshift

I got confused while reading about the cosmological redshift. Take an expanding Universe. If you look a galaxy moving with the Hubble flow, you will see the light...

## Why is there a factor of $hbar$ in the physicists' $mathfrak{su}(2)$ Lie algebra?

The standard (mathematicians') basis for the $mathfrak{su}(2)$ Lie algebra is:$$X_j = -ifrac{sigma_j}2$$ where $sigma_j$ are the Pauli matrices. In physics, observables correspond to real numbers, so...

## 2D ising model explains phase transition (Para-ferro) in 3D space How?

2D ising model explains phase transition (Para-ferro). How come a 2-D model explain a system where spins are distributed in all three directions?...

## What is the connection between the Poynting vector (EM transverse wave) and the description of photons with $E=h*f$ and $c=f*lambda$?

I think for radio antenna transmitters, if the AC current's frequency is at the frequency of radiowaves, EM waves in the radio frequency will be emitted? Then the frequency has...

## Magnification in Holographic Microscopy

The book "Introduction to Optics" by Frank, Leno, and Leno Pedrotti, Ed 3, makes the claim that It can be shown that if the reconstructing light of wavelength $lambda_r$ is...

## Momentum Space Representation of the Tight Binding Hamiltonian

I am trying to represent the tight-binding Hamiltonianbegin{equation}hat{H}_{TB} = sum_{sigma} sum_{alpha,beta} sum_{mathbf{R}_1,mathbf{R}_2}t^{alpha,beta}_{mathbf{R}_1,mathbf{R}_2}hat{c}^{dagger}_{alpha,mathbf{R}_1,sigma}hat{c}_{beta,mathbf{R}_2,sigma}label{eq:Htb}tag{1}end{equation} in the momentum space, and it is not clear this...