# Recent content by krhisjun

1. ### Thermodynamics, two equal volumes of gas at STP mix, entropy change?

As far as ive researched it is infact zero due to the fact that the molecules are indistinguishable from each other, the partition can just be reinserted and the thermodynamic state is the same so it hasnt changed in entropy.
2. ### Thermodynamics, two equal volumes of gas at STP mix, entropy change?

but how do i go about proving entropy change is zero
3. ### Thermodynamics, two equal volumes of gas at STP mix, entropy change?

Homework Statement Calculate entropy change if two equal volumes of gas (1 cm3) at standard temperature and pressure are separated from each other by a partition which is removed to create twice the volume at standard temperature and pressure Homework Equations dS = k.N. dV/V + C/T dT...

5. ### Characterize a co2 TEA class 4 laser

Homework Statement Im working on a lab experiment in my undergraduate physics degree requiring the use of a class 4 laser, i need to characterize this in terms of its power, coherence, pulse duration, wavelength and irradiance. This is a pulsed laser with rough parameters of 1-2J pulse energy...
6. ### Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

Thats a good link but doesnt explain the significance of the areas of the umbra and penumbra areas shamefully....
7. ### Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

Can anyone explain the significance of the umbra and penumbra areas?
8. ### Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

Ive jsut spoken to a friend that used photoshop and the lasso tool to outline the areas then using one of the options it will give a pixel count. i can understand how this will give me the area, and thus the ratio, but not how i could quantify any errors in this calculation.. Thanks for the reply
9. ### Easy Question, Sunspots Astronomy Umbra and Penumbral sunspot areas

Didnt know if this is the write palce to put this, but im stuck on this assingment and i think it must have an easy solution so if someone could point me in the right direction then it would be much appreciated. Homework Statement Using an appropriate software package, quantify the...
10. ### Calculating values of electric and amgnetic fields of laser beam

Ok, didnt realise that equation, so using those values E = \sqrt{2S\mu c} ? Therefore E = 119959.9933 V m^-1 ? H = E/c\mu ? Therefore H = 318.4160428 A m^-1 ? I tried to confirm the equations using dimensional analysis: E = V m^-1 mu= kg·m·s−2·A−2 C = m S^-1 S = J s^-1 m^-2 I cant get that...
11. ### Calculating values of electric and amgnetic fields of laser beam

for fear of asking the obvious, S being?
12. ### Calculating values of electric and amgnetic fields of laser beam

Sorry, i mean to say i dont know how i would get H B or E. i can see easily how with any of the variables allows the other for calculation but im at a loss to get any.
13. ### Calculating values of electric and amgnetic fields of laser beam

Bu then HHow do i calculate H?
14. ### Calculating values of electric and amgnetic fields of laser beam

Homework Statement A continuous wave laser beam in free space carries a power of 15w and has a circular cross section with diameter 1mm. Calculate peak values of the oscillatory electric and magnetic fields Eo and Ho repectively. Homework Equations Eox = (\mu/\epsilon)^1/2 Hoy \pir^2...
15. ### Calculate capacitance to adjust current in ac circuit

Homework Statement A Purely resistive resistive 100w, 110v lamp is to be supplied by an a.c. source of 230v r.m.s at 50Hz. what value of pure capacitance could be put in series to adjust the current flow to a suitable value? Homework Equations p=iv q=cv v=ir i know a number of other...