# Search results

1. ### Metal sheets of various mass left out in the Sun

Yes that makes sense, thanks again. You've been very helpful so I am going to push my luck and ask if you have any criticism of my logic for part b)?
2. ### Metal sheets of various mass left out in the Sun

Ok great, thanks. That has cleared it up for me - but just to fully make sure I have another hypothetical for you if you don't mind: Now we have one thin sheet and one cube, again the same type of metal. The front surface areas of both are equal which means the same amount of radiation is...
3. ### Metal sheets of various mass left out in the Sun

So let's assume they have been left in the sun for a long time and are in equilibrium. Each sheet will be at the same temperature right? But the amount of heat hitting each sheet (therefore the amount of heat lost to the surroundings) is also the same. So the air on the surface of each sheet...
4. ### Metal sheets of various mass left out in the Sun

Actually thinking about it a bit more, for a) if the sheets have the same dimensions therefore the same exposed surface area, would the amount of heat Q hitting the sheets be constant? Because the same amount of radiation will be hitting each one? Edit: I think I'm confusing myself. The...
5. ### Metal sheets of various mass left out in the Sun

These are questions I've made up to try and wrap my head around the topic, so the theory within the questions themselves might be flawed. 1. Homework Statement There are a number of metal sheets that are similar in every way except they each have slightly different masses. The temperature of...
6. ### Which of the SEMF terms account for low A binding energy?

Homework Statement Which of the semi-empirical mass formula terms accounts for a drop in stability at low A and why? Homework Equations B = avA - asA\frac{2}{3} -acZ(Z-1)A\frac{-1}{3} -aa(A-2Z)2A-1 ± apA\frac{3}{4} The Attempt at a Solution I'm struggling getting my head around this one. The...
7. ### Working out magnetic moment and electric quadrupole moment

I think I may be wrong about the electric quadrupole moments, it's possible that only protons contribute to Q. So because the only thing that changes with oxygen isotopes is neutron number Q will be 0 for all of them? EDIT: scratch that neutrons do actually contribute as they attract the...
8. ### Working out magnetic moment and electric quadrupole moment

Could somebody check if I have done this correctly please? 1. Homework Statement Draw the shell filling for oxygen isotopes and make predictions of their nuclear spin, parity, magnetic moment and electric quadrupole moment. Homework Equations Magnetic moment μ = gj j μN Electric quadrupole...
9. ### Equation for neutron proton-fusion, and deuterium photodiss.

Forgot I had posted this question. Thanks!
10. ### Equation for neutron proton-fusion, and deuterium photodiss.

Homework Statement Write the equations for neutron and proton fusion to form deuterium and for deuterium photodissociation. Homework Equations The Attempt at a Solution There is plenty on proton-proton fusion to form deuterium, but not much on proton-neutron. Is it simply p + n -> D ? Is...
11. ### Using nuclear shell model to determine parity and spin

Great, thanks for the help.
12. ### Using nuclear shell model to determine parity and spin

I'm pretty sure we'd only be working with the first one, the Nilsson diagram looks more advanced. Going off the first diagram it looks like our lone neutron would be in the 1f\frac{7}{2} shell where nuclear spin j = \frac{7}{2} and parity = (-1)3 [to the power 3 because it is in the f shell] =...
13. ### Using nuclear shell model to determine parity and spin

Homework Statement Use the shell model to determine the parity and spin assignments for all the stable isotopes of calcium. Homework Equations n/a The Attempt at a Solution The stable isotopes seem to be 40Ca, 42Ca, 43Ca, 44Ca, 46Ca, and 48Ca I believe all of those isotopes except 43Ca are...
14. ### Calculating irradiance from lux of a halogen lamp

Hi all. We're currently working on a project and need to know the irradiance hitting a steel sheet some distance away from a halogen lamp. The setup looks like: The problem is we can only measure the lux at the surface of the steel sheet, and I believe in order to convert lux to irradiance...
15. ### No idea how to word this. Finding the gradient with vector?

Hmm I think I may have to post the question in full. My original post is just a small part of a bigger question (about Gauge transformations) so I am probably going about it wrong.
16. ### No idea how to word this. Finding the gradient with vector?

Sorry it is a vector. I was trying to mimic exactly how it is written in front of me.
17. ### No idea how to word this. Finding the gradient with vector?

Homework Statement I need to find Λ using the equation below (I think). Homework Equations A [/B]+ ∇Λ = 0 where A(x,y,z,t) = B\begin{pmatrix} x+y\\ x-y\\ 0 \end{pmatrix} The Attempt at a Solution Is this at all possible?
18. ### Compare & contrast properties of strong & weak interactions

For those who might read this in future, my lecturer came back to me with a few things more that should be said: Gluons are massless, leading to a long-range force. They couple to colour (carried by quarks) and also carry composite colour, so can interact with each other, which leads to...

Bump
20. ### Compare & contrast properties of strong & weak interactions

Hi all - in the question below I could do with some help on the "..explanation for the relative strengths..." bit, as I can't think of anything to say. 1. Homework Statement Compare and contrast the properties of the strong and weak interactions. Include in your account an explanation for the...
21. ### Calculate the wavelength of the n= 4 -> 3 transition in He

I had no idea the equation would differ. Just looked up 'Rydberg formula' and a Z2 appears. Big thanks, I was beginning to pull my hair out.
22. ### Calculate the wavelength of the n= 4 -> 3 transition in He

Homework Statement Calculate the wavelength of the n = 4 → 3 transition in 4He+ to an accuracy of 4 significant figures. (R∞=109 737 cm-1.) (Fine structure effects can be neglected.) Homework Equations \frac{1}{λ} = \frac{m}{m_e} R_∞ (\frac{1}{n_1^2} - \frac{1}{n_2^2}) where λ is wavelength...
23. ### Can't get my head around reduced mass (particle physics)

I will create a new thread with proper formatting, and pose the question as a whole - so could you delete this thread please? Edit: properly formatted thread at https://www.physicsforums.com/threads/calculate-the-wavelength-of-the-n-4-3-transition-in-he.791525/
24. ### Can't get my head around reduced mass (particle physics)

Hi Orodruin I'll give you the full question to give a better understanding- Calculate the wavelength of the n = 4 → 3 transition in 4He+ to an accuracy of 4 significant figures. (R∞=109 737 cm-1.) (Fine structure effects can be neglected.) Now the equation that I'd use for this is...
25. ### Can't get my head around reduced mass (particle physics)

I know it's probably simple but I just don't understand reduced mass. I am trying to work out the reduced mass of 4He+. m = memN / me + mN Can somebody please just explain step by step what I do. This is only a segment of a 1 mark question and I'm getting my knickers in a frustratingly twisty...
26. ### Lennard-Jones Potential: Derive an expression for equilibrium constant

Finally found a similar question in the depths of the internet and looks like it is right, so all is good here.
27. ### Lennard-Jones Potential: Derive an expression for equilibrium constant

Edit: well this is frustrating, not sure why the itex things aren't working.. Edit2: I've attached a picture of the question at the bottom as well. Homework Statement The cohesive energy of a solid noble gas may be written as (See picture below) Derive an expression for the...
28. ### Entropy change of melting ice cube initially at -5°C

Great, thanks
29. ### Entropy change of melting ice cube initially at -5°C

Homework Statement Calculate the entropy change of an ice cube of mass 10g, at an initial temperature of -5°C, when it completely melts. cice = 2.1 kJkg-1K-1 Lice-water = 3.34x105 Jkg-1 Homework Equations dQ = mcdT dS = \frac{dQ}{T} ΔS = \frac{Q}{T} Q = mL The Attempt at a...
30. ### Diffraction with a large array of slits

I've had a look all round but can't seem to find anything that helps, unless I'm missing something obvious. I've played around with a few applets as well. The things I found focused on the first equation, and the questions would often be "find the #th maxima" with slit width etc given. The 90...
31. ### Diffraction with a large array of slits

From the second equation it looks like as the slit width increases the angle between maxima will decrease. Am I able to set the two equations equal to each other? If so as slit width approaches slit separation the diffraction order will go to 1. Thanks for the reply btw.
32. ### Diffraction with a large array of slits

Hi all, exams soon and I'm stressing out over this small question. If anyone could guide me through, explaining why you're doing what you're doing that'd be beyond great. I posted this in the introductory thread but with no replies thought I should move it here (unsure of how to delete the other...
33. ### Diffraction with a large array of slits

Hi all, exams soon and I'm stressing out over this small question. If anyone could guide me through, explaining why you're doing what you're doing that'd be beyond great. Homework Statement Light of wavelength λ is incident normally on a screen with a large array of slits having equal widths...
34. ### [Statistical Physics] Microstates in a large system/Boltzmann entropy

Ah that's good then. I just thought it was an unreasonably large number. JK^{-1}
35. ### Thermal conductivity and Debye temperature

Hi all Homework Statement The Debye temperature of argon is 92 K and that of silicon is 345 K. Rank the following in order of thermal conductivity (largest value first): (i) A 1 cm3 cube of silicon at 6 K (ii) A 512 mm3 cube of silicon at 2 K (iii) A 1 mm3 cube of argon at 4 K (iv)...
36. ### [Statistical Physics] Microstates in a large system/Boltzmann entropy

Maybe a mod could move this into the Advance forum?
37. ### [Statistical Physics] Microstates in a large system/Boltzmann entropy

Shameless bump
38. ### [Statistical Physics] Microstates in a large system/Boltzmann entropy

Homework Statement For a box containing 1m^{3} of nitrogen at S.T.P., estimate the number of microstates which make up the equilibrium macrostate. Homework Equations S = Nk_{b}(ln\frac{V}{N} + \frac{5}{2} + \frac{3}{2}ln\frac{2πmk_{b}T}{h^{2}}) where the entropy of a volume, V ...
39. ### [Statistical Physics] No. of dice rolls so prob of getting a 6 is >90%

"At least"... such a rookie mistake missing something like that. It's unreal how much time I've just wasted. Thanks, I've got it now.
40. ### Stuck on an equation involving powers - I only have 1 unknown

Thanks but I have probably just messed up somewhere, as I don't think it will be that much hassle. https://www.physicsforums.com/showthread.php?p=4716123#post4716123
41. ### [Statistical Physics] No. of dice rolls so prob of getting a 6 is >90%

This question is really wearing me out, any ideas? Homework Statement How many times must I throw a fair dice in order to make the probability of getting at least one ‘6’ greater than 90%? With this many throws, what is the probability of getting three ‘6’s? It's the first part I'm...
42. ### Stuck on an equation involving powers - I only have 1 unknown

It represents the rolls of a dice. I'm going to post the full question over in the physics homework subforum.
43. ### Stuck on an equation involving powers - I only have 1 unknown

Ah I guess I've gone wrong somewhere. Yes the N's are the same.
44. ### Stuck on an equation involving powers - I only have 1 unknown

Sorry I meant how do I simplify the inequality, ie N > #
45. ### Stuck on an equation involving powers - I only have 1 unknown

Hi all sorry the title couldn't be more descriptive. I'm having a bit of a brain block with this equation (it's the very end of a problem). N(\frac{5}{6})^{N-1} > \frac{27}{5} My line of thought was to get the first N in terms of the power N-1.. How do I find N?
46. ### [Statistical Physics] Probability of finding # photons in the mode

Ooh thanks for pointing that out, I accidentally put a minus in there.
47. ### [Statistical Physics] Probability of finding # photons in the mode

Ok think I've got the relevant equation for a) and b) now. For any future readers: P(n) = \frac{1 - exp(-\frac{ħw}{kT})}{exp(\frac{nħw}{kT})} where n is the number of photons in the mode.
48. ### [Statistical Physics] Probability of finding # photons in the mode

You've just made me realize the equation should have a -1 on the bottom. Can't edit my original post for some reason.
49. ### [Statistical Physics] Probability of finding # photons in the mode

Ah ok, so the mean number of photons might still be ok. How do I go about answering a and b?
50. ### [Statistical Physics] Probability of finding # photons in the mode

Homework Statement A cavity contains black body radiation at temperature T = 500 K. Consider an optical mode in the cavity with frequency ω=2.5x10^{13} Hz. Calculate a) the probability of finding 0 photons in the mode b) the probability of finding 1 photon in the mode c) the mean number...