## Wavelength/frequency

Moderators: Chem_Mod, Chem_Admin

paulacamara1E
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

### Wavelength/frequency

Why does energy decrease when wavelength increase? My TA explained the concept in discussion but I don't think I fully got it.

Chem_Mod
Posts: 17238
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 367 times

### Re: Wavelength/frequency

When wavelength increases, the EM radiation's frequency decreases. Since energy of a photon is E = hv, energy of the photon must decrease since frequency v decreased.

Michael Park
Posts: 30
Joined: Fri Apr 06, 2018 11:04 am
Been upvoted: 1 time

### Re: Wavelength/frequency

Energy = [(Planck's Constant) x (Speed of light)] / [wavelength]

Because wavelength is in the denominator, as the wavelength increases, energy decreases.

fara valdez
Posts: 48
Joined: Fri Apr 06, 2018 11:05 am

### Re: Wavelength/frequency

I guess it's the conservation of energy, if the speed changed then this would require an acceleration which would need energy to be put in or taken out of the wave.

Chem_Mod
Posts: 17238
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 367 times

### Re: Wavelength/frequency

It is not conservation of energy.

Miya Lopez 1I
Posts: 62
Joined: Tue Nov 14, 2017 3:00 am
Been upvoted: 1 time

### Re: Wavelength/frequency

Increasing the wavelength decreases the kinetic energy of ejected electrons because when you have E=hv, and you substitute in the frequency (v) as c/(lambda) you get.. E= h * c/(lambda).

So when you increase the wavelength, lambda, it makes the fraction c/(lambda) a smaller number overall which means the energy decreases.

I hope the way I explained it makes sense and helps.

Daniel Cho Section 1H
Posts: 29
Joined: Fri Jun 23, 2017 11:40 am

### Re: Wavelength/frequency

It is good to think of it with the equation E=(Planck's constant)(frequency) and speed of light=(wavelength)(frequency). An important skill is linking these two equations together.
Let's try solving for frequency with the equation speed of light=(wavelength)(frequency) which the equation would end up being frequency=(speed of light)/(wavelength). Since E=(Planck's constant)(frequency) you can substitute frequency with the equation we just manipulated which would up being E=((Planck's constant)(speed of light))/(wavelength).

Energy increases as wavelength decrease because of the idea of these two variables being inversely proportional as demonstrated by the equation we just manipulated.

I hope this helps, correct me if I am wrong in some places.

Elana Weingord 1C
Posts: 34
Joined: Fri Apr 06, 2018 11:05 am

### Re: Wavelength/frequency

It is important to note that when the wavelength increases, the electro magnetic radiation's frequency decreases. Since energy of a photon is expressed through the formula E = hv, energy of the photon must decrease since frequency decreased.

Phil Timoteo 1K
Posts: 101
Joined: Fri Apr 06, 2018 11:05 am

### Re: Wavelength/frequency

Because E=hv and if the wavelength increases that means the frequency would decrease.

Jose Hernandez 1D
Posts: 16
Joined: Tue Nov 14, 2017 3:02 am

### Re: Wavelength/frequency

Because E=hc/lambda wavelength is the denominator and the greater the wavelength means the less energy you have since the variables h and c are constants.

KristinaNguyen_1A
Posts: 30
Joined: Fri Apr 06, 2018 11:04 am

### Re: Wavelength/frequency

Energy decreases when wavelength increases because as wavelength increases, the wave frequency decreases (due to the fact that they are inversely proportional) because larger wavelength means fewer waves. Wave frequency gives off energy so if wavelength increases=frequency decreases, then energy also decreases.

Maria Zamarripa 1L
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am
Been upvoted: 1 time

### Re: Wavelength/frequency

conceptually, I think it's because since the wavelength is longer there are fewer cycles per second so it is moving slower and has less energy.

Return to “Properties of Light”

### Who is online

Users browsing this forum: No registered users and 1 guest