Physics Help Forum Homework questions on quantum theory (blackbody radiation)

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 Oct 4th 2008, 10:42 PM #1 Junior Member   Join Date: Oct 2008 Posts: 1 Homework questions on quantum theory (blackbody radiation) Hello.. i need help with two homework questions if anyone would be so kind. I do not know where to begin on solving these questions. The questions are as follows: 1. If the angular frequencies of waves in a three-dimensional box of sides L generalize to: Ω = πc/L (nx²+ny²+nz²)^1/2 Where all n are integers, show that the number of distinct states in the frequency interval f to f + Δf (f=Ω/2π) is given by (where f is large) dN = 4π(L^3/c^3)f²df 2. Let the energy density in the frequency interval f to f + df within a blackbody at temperature T be dU(f,T). Show that the power emitted through a small hole of area ΔA in the container is c/4dU(f,T)ΔA THANK YOU!
 Oct 28th 2008, 03:31 AM #2 Junior Member   Join Date: Oct 2008 Posts: 2 Hi, I may help you with the first task. We have f=c/2L (nx²+ny²+nz²)^1/2 (1) So with common f we have a (1/8) of a sphere with radius r = (nx²+ny²+nz²)^1/2=(2L/c)f the area of this (1/8) of a sphere is πr^2/2 = (1/2)π(f 2L/c)^2 Now, as we want to count the triples (nx, ny, nz) for which f given by (1) falls between f and f+df we need to to find the "thikness" of the sphere, which is dr=(2L/c)df. Thus we get number of states = πr^2/2 dr = (1/2)π(f 2L/c)^2(2L/c)df = 4π(L/c)^3f^2df best regards Last edited by katastrofa_nadfioletu; Oct 28th 2008 at 10:34 AM. Reason: lots of spelling errors
Oct 28th 2008, 01:55 PM   #3
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I decided to enclose a picture of the situation . Hope this help as well as equations!
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 Dec 20th 2008, 06:43 PM #4 Junior Member   Join Date: Dec 2008 Posts: 1 Radiation Physics Glance at: Radiations -- Abdurrazzak.
 Feb 17th 2009, 03:52 AM #5 Junior Member   Join Date: Feb 2009 Posts: 6 Assignment help , homework help , Project help , online homework. Here is the address for the site: Assignment help We have passionate and dedicated subject experts who takes care of all worries, with an affordable solution. At Assignment Help. Help with examination preparation SAT PSAT LSAT ACT AP CLEP Key Stage 1-4 GCSE AS / A Levels Mathematics, Physics, Chemistry, Biology, Statistics, Managerial Accounting and Computer Science. Engineering (Computer, Electrical, Mechanical, civil ,Chemical, Textile and Fashion technology) Accounts / Finance, MANAGERIAL ACCOUNTING, Economics, Statistics, Market Research, Data analysis, Report formatting, Consumer NPV, IRR, YTM,survey, Content development, Operational Research, Business case studies. Advanced level stats, ARCH , GARCH , TIME SERIES, ARMA, ARIMA, MULTI VARIATE ANALYSIS , AUTO REGRESSIVE MODEL Papers and essays. We help in following areas: Cash Flow Statement Funds FlowFutures, Options, Swaps Financial Statement Analysis / Reporting Capital Budgeting Security Analysis. Cheers! willy

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