Calculating energy of photon of light

[newtochem]

I am new to chemistry and i am stuck on something easy i am sure, i think that i am missing something. So anyone please help i have a major test tommorrow.

 

THe question is helium has a wavelenth of 589nm. Calculate the energy of this photon of light. Now i do know that(1nm=10 -9m) this is the part that i dont understand. how to covert to the 2nd part of the wavelength i think.

If someone could help me breakdown this problem i would be grateful. :)

[Essay]

Isn't there some equation like Energy = h times gnu.

 

h is Planks constant, I think.

...and nu is the wavelength.

 

just make sure the units match up correctly.

...and that you cancel the units correctly (if your answer has the right units, then you probably did it right).

 

Good luck (or hopefully someone will correct this if needed).

 

~ :)

 

p.s. ...or is that the question: how to get to the right units?

[modest]

You are correct that 1nm = [imath]10^{-9}[/imath] meters. You can use this relationship to express your wavelength in meters.

[math]589 \ nm \left( \frac{10^{-9} \ m}{1 \ nm} \right) = 5.89 \times 10^{-7} \ meters[/math]

If you have the wavelength of a photon expressed in meters (which we just found) then you can find it’s energy by using this equation:

[math]E = \frac{h \times c}{\lambda}[/math]

where

• E is energy in Joules
  
• h is Plank’s constant in Joule-seconds or [math]6.626 \times 10^{-34} \ J \ s[/math]
  
• c is the speed of light in meters/second or [math]3 \times 10^8 \ m/s[/math]
  
• [math]\lambda[/math] is the wavelength in meters which we found above: [math]5.89 \times 10^{-7} \ m[/math]
  

 

In other words, multiply Plank's constant and the speed of light then divide by the wavelength. Be sure to express everything in Joules, meters, and seconds and you're answer will be the energy of the photon in Joules. Try it out - I'll check your answer.

 

~modest

[Essay]

Aha! Thanks for jumping in with a more complete (and correct) explanation.

I was close, but just mixed up frequency and wavelength, eh?

freq. (nu) = c/wavelength (lambda)

right?

Thanks mucho,

;)

 

You are correct that 1nm = [imath]10^{-9}[/imath] meters. You can use this relationship to express your wavelength in meters.

[math]589 \ nm \left( \frac{10^{-9} \ m}{1 \ nm} \right) = 5.89 \times 10^{-7} \ meters[/math]

If you have the wavelength of a photon expressed in meters (which we just found) then you can find it’s energy by using this equation:

[math]E = \frac{h \times c}{\lambda}[/math]

where

• E is energy in Joules
  
• h is Plank’s constant in Joule-seconds or [math]6.626 \times 10^{-34} \ J \ s[/math]
  
• c is the speed of light in meters/second or [math]3 \times 10^8 \ m/s[/math]
  
• [math]\lambda[/math] is the wavelength in meters which we found above: [math]5.89 \times 10^{-7} \ m[/math]
  

 

In other words, multiply Plank's constant and the speed of light then divide by the wavelength. Be sure to express everything in Joules, meters, and seconds and you're answer will be the energy of the photon in Joules. Try it out - I'll check your answer.

 

~modest

[modest]

Aha! Thanks for jumping in with a more complete (and correct) explanation.

I was close, but just mixed up frequency and wavelength, eh?

freq. (nu) = c/wavelength (lambda)

right?

Thanks mucho,

;)

 

Yes. Sorry, I missed your post or I certainly would have acknowledged you were on the right track. The frequency is c divided by wavelength as you say.

[math]E= \frac{hc}{\lambda} = h \nu[/math]

 

~modest