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May 5, 2016
Posted by **noah** on Wednesday, February 22, 2012 at 1:27am.

- college physic -
**Kty**, Wednesday, February 22, 2012 at 3:07amFirst you get to know the surface area of a sphere, that is A=4*pi*r^2

All the info listed down:

Emissivity,e=1 (blackbody has a good emissivity)

radius,r=0.30m

Temperature, T2=77K T1=4.2K

Latent heat of vaporization,L=2.1*10^4 J/kg

Time,t=1hour=3600sec

First, use the Steven-Boltzman Rule,

Power,P=Q/t=e*sigma*A*(T2^4-T1^4)

Thus, we get

P=1*(5.67x10^-8)*4*pi*(0.30)^2*(77^4-4.2^4)

P=2.254 J/s

Then as we found Power,and time=3600sec

Substitute into the formula, Q=Pt

Thus, we get

Q=2.254*3600 =8115.16Joule

Refer to the question the Latent heat is given, we calculate for the mass with the formula, Q=mL

m=Q/L =8115.16/(2.1*10^4) =0.386kg

hope i do get it right. :) - college physic -
**noah**, Thursday, February 23, 2012 at 4:07amoo

thx dude