# What is Particle: Definition and 997 Discussions

In the physical sciences, a particle (or corpuscule in older texts) is a small localized object to which can be ascribed several physical or chemical properties such as volume, density or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans moving in a crowd or celestial bodies in motion.
The term 'particle' is rather general in meaning, and is refined as needed by various scientific fields. Anything that is composed of particles may be referred to as being particulate. However, the noun 'particulate' is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

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1. ### Probability of finding a particle in the right half of a rectangular potential well

Hi guys it's me again. I need help with this exercise which reads: a particle of mass m, placed in an infinite rectangular one-dimensional potential well that confines it in the segment between ##x = -\frac{a}{2} and x=\frac{a}{2}##, is at instant ##t=0## in the state: ##|\psi \rangle =...
2. ### Instantaneous Acceleration Given Equation for Velocity

This is from an old exam. The velocity of a particle moving along a straight line is v = 4 + 0.5 t. What is the instantaneous acceleration at t=2? The solution is supposedly 2 because a = dv/dt = t. But I thought dv/dt here would be 0.5. What am I missing? Thanks.
3. ### Wave function of infinite potential well

Hi guys i have this exercise: A particle of mass m, confined in the segment -a/2 < x < a/2 by a one-dimensional infinite potential well, is in a state represented by the wave function: 1. Determine the constant N from the normalization condition. To do this, I have to integral the square...
4. ### B The Origins of the Wave Particle Duality

https://bigthink.com/starts-with-a-bang/surprising-origins-wave-particle-duality/
5. ### Final speed of particle far away from rings with opposite charges

When I submitted it, this answer was incorrect.
6. ### I Why do we say that wave amplitude tells us where we are likely to find the particle?

Why do we say that wave amplitude tells us where we are likely to find the particle versus where we are likely to find the wave from the particle? Isn't the later a more accurate description of the QM math?
7. ### I How often would a ϕ meson decay to a electron-positron pair?

I know the mass of J/ψ to be 3097 mev and the mass of phi to be 1018 mev. I know that J/ψ decays to electron and positron 5% of the time. I also know the full width of j/psi to be 0.092mev and that the phi meson lives 50 times longer than J/ψ . My professor claims that if I am given that info...
8. ### Plotting the trajectory of a particle in polar coordinates

Hi, Unfortunately, I am not quite sure whether I have solved/plotted the following task correctly I started by resolving the expression ##\phi=2 \pi t## to t so that I can represent ##\rho(t)## with ##\rho(\phi)## The vector ##\vec{e}_r## was written in my lecture as follows...
9. ### Find the linear speed of the particle when system rotates about axis

Question image: The question should be solved by conservation of mechanical energy.( I assume surface density##\sigma## and acceleration due to gravity##g=const.##)Therefore: $$PE_i+KE_i=PE_f+KE_f$$ The axis of rotation ##PQ## is line of zero potential. Then 1) ##PE_i=\int Fdy## Since...
10. ### How to convert to the number of sand and Nylon particles from mass

I calculate 4.8x10(^10) particles /kg of sand in the sample. Do you find the same ? Is my solution correct ? How many particles do you find ? Thanks in advance !
11. ### I Relativistic Lagrangian of a particle in EM field

I'm following the derivation in Lancaster and Blundell. First, the Lagrangian for the free particle is ##L=-\frac {mc^2} {\gamma}## and the action ##S=\int -\frac {mc^2} {\gamma} \, dt##. Then, EM is "turned on" with the potential energy ##-qA_{\mu}dx^{\mu}##. Then, they say, the action becomes...
12. ### Particle experiencing only an angular force, determine the r dot

Hey, I've been working on this for a couple hours, and still no luck. Since the force in the radial direction is zero, I set r'' = rθ'^2. Then since Fθ = m r' θ' and, since it's in polar coordinates, Fθ = m(2r'θ' + rθ''). Setting these two equal, I get: -r'θ' = rθ'' At this point, I'm...
13. ### Particle moving from one potential to another

Attaching the image of the problem as an image. Somehow text is not copied from the book. Somehow, I can't imagine the picture in my head. We can do it in 2D plane. I know, it mentions the solution, but need to see the drawing, otherwise, my logic fails. I thought that maybe, first half space...
14. ### Calculate Distance Traveled: Instantaneous vs. Average Velocity

edit: I don't know why my latex isn't rendering, any help would be appreciated. Edit 2: The question was due to a misunderstanding I had, I thought integrating instantaneous velocity would give me average velocity. I have attached what I have tried so far. I had a doubt. Can you calculate the...

26. ### B How to show that particle spin includes angular momentum?

I understand how a massive, electrically charged spinning ball would have both angular momentum and a magnetic dipole, and i can see how the Stern–Gerlach experiment shows that the magnetic dipole of an electron is quantized. What kind of experiment demonstrates a connection between electron...
27. ### B What exactly is spin? Does the standard model work without spin?

I did some research online and found that "When certain elementary particles move through a magnetic field, they are deflected in a manner that suggests they have the properties of little magnets." To explain this phenomenon, physicists invented the concept of spin. So far so good. What I...
28. ### Why a particle with spin=0 can't posses a magnetic dipole moment?

Hi, I would like to know why a particle with spin=0 can't posses a magnetic dipole moment? Using Wigner-Eckart theorem for ##\langle j,1,m,0|j,m \rangle## I get ##\langle j'|| \vec{J}|| j \rangle = \hbar \sqrt{j(j+1)} \delta_{jj'}## It seems like the right hand side is the magnetic dipole...
29. ### B Magnetic Field & Particle Spin: Does It Matter?

Does the magnetic field caused by moving particles depend on the particle spin value? Eg a stream of say protons spin 1/2 is creating a magnetic field. If the particles are (say) lithium nuclei spin 3/2 instead, does that create the same strength field ? (same conditions of course)
30. ### MCNP6.2 - Source particle started in a cell of zero importance

Hi everyone, My plan is defining a surface source on a cylindrical object (cylindrical surface+top end+bottom end) and I am interested in what happens outside the cylindrical body. To avoid distortions of particles starting on the surface, directed inwards and emerging on the other side of the...
31. ### A particle in an infinite square well

What I am lost about is b, rather the rest of B. I am not sure what it means by probability density and a stationary state.
32. ### A Symmetries of particle interacting with external fields (Ballentine)

I am following along with Ballentine's (in his *Quantum Mechanics: A Modern Development*) construction/identification of symmetry generators as operators representing the standard observables (observables here being used in the sense of a physical concept which have operators representing them)...
33. ### I Free particle probability distribution

Abstract: If a laser shoots photons at a pinhole with a screen behind it, we get a circular non-interference pattern on the screen. Is this distribution Guassian, and if not, what would its wave function be? ===================== Assume a double-slit like experiment, but instead of double...
34. ### Problem 2 in "Quantum Theory for Mathematicians", Solving for the travel time of a particle in a potential

I’ve been trying to solve this for ages. Would really appreciate some hints. Thanks
35. ### Electric Flux through a semi-spherical bowl from a charged particle

I believe this does has a couple of Calculus aspects to it but I don't really know how I'd find the surface area of inside the bowl. The answer sheet says the answer is 252 with a margin of error of +/- 1
36. ### Determine the Lagrangian for the particle moving in this 3-D cos^2 well

Hi, I am not quite sure whether I have solved the following problem correctly: I have now set up Lagrangian in general, i.e. $$L=T-V=\frac{1}{2}m(\dot{x}^2+\dot{y}^2)-mgz$$ After that I imagined how ##x##,##y## and ##z## must look like and got the following: x=\beta \cos^2(\alpha r)...
37. ### A Exploring Secondary Particle Generation from X-Ray Collisions in Geant4

Hello, I need some articles and pictures about secondary particle generation when x-ray(with different energy) collides with silicon and aluminium materials. I am simulating this phenomenon in geant4. I just want to validate my result.
38. ### Time Independence of the Momentum Uncertainty for a Free Particle Wave

Mine is a simple question, so I shall keep development at a minimum. If a particle is moving in the absence of a potential (##V(x) = 0##), then ##\frac{\langle\hat p \rangle}{dt} = \langle -\frac{\partial V}{\partial x}\rangle=0## will require that the momentum expectation value remains...
39. ### B Particle creation and annihilation

I read somewhere that when, say, an electron and positron annihilate, they create two photons which travel in opposite directions in order to conserve linear momentum. Is this true? What about pair production. Do you likewise need two photons to do this? Or, can you do it with one photon...
40. ### Finding a Parametric Solution for Particle Trajectory in Magnetic Field

This is a solution to a problem inspired by another thread. It is posted here to separate it from the multiple choice question which was the subject of that thread. A parametric solution for the trajectory can be found quite easily if the motion is modeled as a particle with charge ##q##...
41. ### I Proving Behavior of Particle in Infinite Potential: Wave Function?

Hello, guys! I have a question. How can I prove the behavior of a particle subjected to an infinite potential? Will the wave function exist?
42. ### Hamiltonian of a Point particle on a frictionless plane

I am stuck on Question e and then how to proceed to f. I cannot seem to show this using the steps in the prior questions. My answers are: a) b) c) c) continued - and d) at the bottom of the page d)I am not sure where I have gone wrong, as I am not sure how to apply the relevant...
43. ### Kinetic energy of an alpha particle

Kindly help me solve this question. The only thing so far that I know in this question is that energy is conserved and the momentum of Alpha particle will equal momentum of Thorium.
44. ### I Removing a proton with a particle accelerator

What would it look like if I used a particle accelerator to remove a proton from a particular element? What would the physical change in the element look like if observed? Would the element appear to "magically" change into something else right before your very eyes, as if by some kind of spooky...
45. ### I Is the superposition of mesons (such as pion) a new particle?

There are 36 hadron composites composed of 2 quarks selectable from the set ##[u, d, c, s, t, b, \bar u, \bar d, \bar c, \bar s, \bar t, \bar b]## satisfying the condition of having total charge = ##[-1, 0, 1]##. However, the superposition states of pure hadrons are sometimes also listed as new...
46. ### B Quantum field theory and wave particle duality

I recently watched this lecture "Quantum Fields: The Real Building Blocks of the Universe" by David Tong where the professor provides a succinct explanation of QFT in about 6 minutes around the midway mark. The main point being that there are fields for particles and fields for forces and the...
47. ### Particle transporting (FLIBE) -Geant4

How can I define FLIBE as a target in Geant4? Extended examples in TestEm11
48. ### Use the energy method to find the distance moved by particle

This is from an examination paper -A level. My interest is on part (ii). Ok my take; i. ##KE_{initial} = \dfrac {1}{2} mu^2= \dfrac {1}{2}× 0.4 ×12^2=28.8## Joules. ii. ##\dfrac {1}{2} mv^2=\dfrac {1}{2} mu^2-mgh## ##0=28.8-(0.4×10×h)## where h is the vertical perpendiculor distance...
49. ### I Shankar on constraints and free parameters for a particle in a box

On page 160 in Shankar, he discusses how we get quantized energy levels of bound states - specifically for the particle in a box. We have three regions in space; region I from ## \ - \infty, -L/2 ##, region II from ## \ -L/2, L/2 ##, and region III from ## \ L/2, \infty ##. For the...
50. ### I How fast does the particle go through spacetime?

This is a very basic question, and I am not sure I have the answer. A photon goes from point A to point B, only 1 meter distance apart from each other. A spacetime diagram would show a line connecting points A and B at a 45 degree angle. This can be a right triangle with equal sides, with...