Recent content by Jenkz

Homework Statement Hello, I'm trying to use a solarimeter (thermopile) to measure the direct flux of solar radiation, in clear conditions, over varying solar zenith angles. The equipment has an output of volts, but I need to convert this to Lux and then convert this to watts per meter...

Homework Statement The equation of state PV= U/3 applies to a photon gas at pressure P, volume V and internal energy U. By using the 'energy equation', show that the internal energy of a phont gas is proportional to the fourth power of temperature (i.e U \proptoT^{4}). You can assume that...

Ok thanks, but I still don't understand how what to do for this question. :S

Is my answer in my first post incorrect? "I know that dQ = 0 as this is an adiabatic expansion. Meaning dU = dW = - NKbT ln (V2/V1)" as dU= dW = (integrating from V1 to V2) - pdV where P = NKbT / V

Homework Statement Derive an equation for the change in entropy that occurs in an isolated (micro-canonical) system containing N particles, if an adiabatic expansion from volume V1 to volume V1 takes place. Show that the number of microstates is given by V^N.Homework Equations Entropy S =...

Homework Statement Show that ln[ (N + M - 1)! /M! (N-1)! ] is equal to N ln((N+M) / N) + M ln((N+M) /M). Homework Equations Using stirling's formula ln N! ~ N lnN - N The Attempt at a Solution ln[ (N + M - 1)! /M! (N-1)! ] (a) = (N+M...

Oh yeah.. that doesn't really make sense :/ Thank you for your help : D!

Also this one please? 1. Homework Statement Assume the Earth's human population increases at 1.25% a year from its present 6.5 billion and reaches 15 billion people (instead of the maximum 12 billion projected by the UN). How many years will that take? The Attempt at a Solution 8.5...

Homework Statement In 1996 the total energy used in the world was 400 million terajoules = 400 exajoules (EJ)= 4 x 10^20J . Projections for energy use vary, but generally it is expected that between 20 and 30TW will be needed by 2025. (a) What percentage growth in energy consumption on an...

Yah.. I just did something silly. All works now! :D

Ooo nvm. Thanks!

I'm still not really getting anywhere with the answer :s so far all I've got is: sinx / x = 1/ √ 2 = 1 - X²/6 + X^4 / 120 - ... Truncating the series and some re-arranging I get 1.752 = X² (1- X² /20 ) But I end upwith something completely wrong... :/

Homework Statement Sin x / x = 1/ (2)^1/2 how do I solve for x? I know x is 1.392 The Attempt at a Solution I thought I might be able to use some series expansion, but it gets quite messy. Help please?

Nevermind, I've got it now. Just a stupid mistake.

Homework Statement http://img228.imageshack.us/i/cimg5162f.jpg/ This isn't the usual format, so I hope it's still ok. It's just easier than writing it out on here. I can't work out how to form a simultaneous equation from (1) and (2). When solved it should form the du/dx and dv/dx...