why do we use these equations?

[connie 2C]

for problem 1B.7, why do we use both c=v/wavelength and E=hv and combine it into one equation? why does using the combined equation give us the energy and not the E=hv equation?

[Jainam Shah 4I]

Both give you energy. In E=hv you would need the frequency. Some times you are given wavelength, thus you use c/wavelength(lambda) to find this frequency. The equation E=hc/lambda is simply a substitution of c/lambda for the original v (frequency).

[connie 2C]

so if you are given frequency, then you would use the equation c=v*wavelength to find the wavelength and then use that to find the energy?

[connie 2C]

also to correct myself in the first post, i meant the equation c=v*wavelength not c=v/wavelength! sorry!

[Ying Yan 1F]

Just from doing some problems, I believe the reason we combined the two equtions is solely dependent on the amount of information given in the problem. For instance, when we are solving for the energy of the photon, we have to combine the equation because we need/ were given wavelenght and thus need to used it to find frequency, etc. (I hope that helps a bit!)

[kendal mccarthy]

Based on the question and the given information, it's kind of like a puzzle where you can use certain equations or combine them to get the information you are looking for!