[A5HLEY]

Hey guys, I'm stuck on a question for test review, and I wanted to get some input.

The question is:

What frequency of radiation has photons of energy 1.97E-19 J?

Now, I know that c = (lambda)(v),  E = hv, and c = 3.0E8, but I'm not sure how to fit the numbers together. Any help would be appreciated!

[enahs]

Why are you trying to combine equations?
You said you know that:
E=hv

You know E (given in problem), h is just a constant, therefor you know v.

[A5HLEY]

Why are you trying to combine equations?
You said you know that:
E=hv

You know E (given in problem), h is just a constant, therefor you know v.

Thanks, I don't know why I must try to make everything so complicated... 

[ARGOS++]

Dear A5HLEY,

I got 1008 nm.   But I calculated it as I usually do, - with “Einstein”

1.00 Einstein of wavelength λ is defined as:
 

ΔE = 2.86 * 10⁴ / λ  [kcal/mole] = 119’719 / λ [kJoule/mole]   - if λ in [nm]

   
With N_A = 6.022 * 10²³ “Particels” / mole you get:
   

λ = 119’719 / (ΔE_P * N_A) = 119’719 / (1.97 * 10^-19  *   6.022 * 10²³) = 1008 nm

It is based on the same Formula as yours:

ΔE = h * v       -  with  v in [cm^-1] and h as the Plank’s Constant

If  you incorporate  λ = c / v you will result in:

ΔE = h * c  / λ      ===>    λ = h * c / ΔE

If you do so, you should get the same as I.
(-Take care for the correct units!-)

“Einstein” and the corresponding nice Diagram you may find under the Question:

What is the Relationship between Wavelength and Energy

on the “Spectroscopy FAQ / Beer-Lambert Bouguer Law FAQ” Page.

Good Luck!

                    ARGOS⁺⁺