Frequency * wavelength ?

[VultureV1]

this may be kinda stupid but isn't frequency * wavelength = velocity ? how is λν = c , that implies that the speed of light is dependent on wavelength and frequency . more importantly . e = hf , and e = h c/wavelength . Should'nt it be e = h velocity/wavelength .

Edited November 4, 2013 by VultureV1

[swansont]

The speed of light is constant, so frequency and wavelength are not independent values — knowing one determines both.

[studiot]

 

this may be kinda stupid but isn't frequency * wavelength = velocity ?

 

 

Yes this is correct.

 

 

how is λν = c , that implies that the speed of light is dependent on wavelength and frequency .

 

 

No. the speed of light is a constant (in a given medium). 'c' is the (constant)speed in a vacuum.

 

This implies that any change to the frequency must be accompanied by a change in the wavelength to maintain that constancy.

 

 

more importantly . e = hf , and e = h c/wavelength . Should'nt it be e = h velocity/wavelength .

 

 

What's the issue here? c is constant so hc is constant so the energy is proportional to the frequency and inversely proportional to the wavelength.

[VultureV1]

Thanks for the reply

and

 

What's the issue here? c is constant so hc is constant so the energy is proportional to the frequency and inversely proportional to the wavelength.

λν = velocity , just any velocity , so why is the assumption made that that particular velocity is c , I can just keep it as e = h velocity/wavelength , why do I put in c .

[Sensei]

Thanks for the reply

and

λν = velocity , just any velocity , so why is the assumption made that that particular velocity is c , I can just keep it as e = h velocity/wavelength , why do I put in c .

 

Theory must be consistent with experimental data, not reverse.

 

If you will send blue light and red light from lasers, they will reach detector at the same moment. So regardless of photon energy, frequency and wavelength, they must have the same velocity.

 

Other example - if you have 3 km long fiber wire, and you will send data at frequency f0 and f1, you will receive data at the same moment 10 microseconds later. If their velocity would be different data would be desynchronized.

[Strange]

Thanks for the reply

and

λν = velocity , just any velocity , so why is the assumption made that that particular velocity is c , I can just keep it as e = h velocity/wavelength , why do I put in c .

 

This relation applies to any wave and you need to use the appropriate velocity for the wave you are considering. For example, if you were concerned with sound waves, you would use the speed of sound. If you are talking about light, you use the speed of light, c.

Other example - if you have 3 km long fiber wire, and you will send data at frequency f0 and f1, you will receive data at the same moment 10 microseconds later. If their velocity would be different data would be desynchronized.

 

Actually, the speed of light through a medium is wavelength dependent.There will be some dispersion of blue and red light in a fibre.