Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jbvaliquette on September 24, 2007, 07:36:56 PM
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if the specific heat of water is 4.184 J/g degrees celcius how many photons of blue light (410nm) are required to raise the temperature of a 5 gallon bird bath 3 degess celcius assuming complete transfer of energy to the water and no influence from the bird bath container.
i just dont know the steps and how the gallons and degress effect it.
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Changing the font colour does not make it a different post...
But I suppose I'll still help:
Use specific heat, change in temp and mass to calculate energy needed (if this doesn't help review what specific heat is).
Energy of photon=hf=h*c/(410*10-9) for photons of the blue light. How many photons are therefore required?
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i still do not understand how the gallons or degrees will effect the answer need step by step info in a plug and chug format if not willing to give answer.
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got answers of .000723 and 4.84829*10^-37 not sure on my answers any help
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No, neither are right, you should only have 1 answer as well. The number of photons should definitely be greater than 1.
What did you do?
Use E=m*C*delta T to find the Energy that is needed to raise the 5 gallons of water by 3 degrees.
(For m, convert 5 gallons to grams)
Number of photons needed= this value/energy of the photons (see my last post)
I think confusion lies with Specific Heat...
C=specific heat=4.184. This means that it takes 4.184J of energy to raise the temp of 1g of water 1 degree. For every gram of water you need 4.184J to raise it's temp by 1 degree, (4.184*2)J to raise its temp by 2 degrees and so on.
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how do you convert gallons to grams when one is a volume and the other is a mass? and what is delta T?
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so 5 gallons equal 18143.6948 grams but what is delta t
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delta t is change in temperature (delta means change)
So in your problem, this is 3.
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so 18143.6948*4.184*3=227740 is that the answer doesnt seem right
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or is the answer 3.8283*10^-10 if so what in what unit
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Your second answer is wrong - it is much to low.
Assuming your conversion from gallons is right (I don't know it off the top of my head - you could probably google it), what you have posted directly after my last reply is the Energy that is required to raise the temp of the water by 3 degrees. You still have to find out how many photons are needed to do this. The number of photons needed will be this value divided by the energy of the photons. Do you know what the energy of the photons are? I put it in one of my earlier posts...
Energy of photon = h*c/wavelength
= 6.626*10-34*3*108/(410*10-9)
(h= Planck's constant, c= speed of light in vacuum)
You are finding out how many photons are needed - the unit for your answer is therefore photons.
*Also, after doing this calculation, convert your answer to the next integer (whole number). Can't have a fraction of a photon.
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if the specific heat of water is 4.184 J/g degrees celcius how many photons of blue light (410nm) are required to raise the temperature of a 5 gallon bird bath 3 degess celcius assuming complete transfer of energy to the water and no influence from the bird bath container.
i just dont know the steps and how the gallons and degress effect it.
Please read forum rules (http://www.chemicalforums.com/index.php?page=forumrules). Don't abuse colors, use informative thread subjects, post your questions only once.
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i got 4.84829^-37 or 4.69732^41
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dont i have to make the 410nm into meters?
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After doing the calculations I described in my last post your final answer is 4.6976 x 1023 photons which resembles your second answer.
Yes, for the Energy of photon equation, wavelength is in meters. If you see my previous post, I have 410*10-9 for wavelength.
(nano=10-9)
Hope that helps!
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so my final answer to the problem is 4.6976 x 10^23
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Yes, assuming your conversion from gallons to grams is ok.
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Yes, assuming your conversion from gallons to grams is ok.
It wasn't
1 US gallon = 18927.06g
1 UK gallon = 22730.46g
1 gallon = 8 pints
1 pint US = 473.176ml
1 pint UK = 568.261ml
for 5 US gallons 4.90x1023 photons
for 5 UK gallons 5.89x1023 photons