Understanding wavelength and frequency.

[sphyics]

"when light enters from one medium to other its frequency remains same whereas wavelength changes."
i'm not able to understand this relation as frequency has a inverse relation to wavelength
please help me to understand it thoroughly.

 

[f95toli]

Yes, but what IS the relation between frequency and wavelength?
Have you looked at the formula?

 

[sphyics]

Yes, but what IS the relation between frequency and wavelength?
Have you looked at the formula?

frequency is inversely proportional to wavelength
and that's where my problem is if wavelength changes how come the frequency remains constant.

 

[DocZaius]

wavelength * frequency = speed

If frequency remains the same and wavelength changes, then speed must change (this isn't a statement of causality, it's just a look at the equation). Light has different speeds in different mediums so it makes sense that it could change.

 

[sphyics]

wavelength * frequency = speed

If frequency remains the same and wavelength changes, then speed must change (this isn't a statement of causality, it's just a look at the equation). Light has different speeds in different mediums so it makes sense that it could change.

i understand, why can't it happen other way frequency changes and wavelength remains same. (and this is what i was pondering about

 

[DocZaius]

i understand, why can't it happen other way frequency changes and wavelength remains same. (and this is what i was pondering about

Good question! I would be interested in the answer too. I have learned that frequency is determined by the source and wavelength by the medium, but I have not learned why each of those properties are tied to each of those factors.

 

[f95toli]

Well, one "handwaving" argument is that the energy of light is proportional to frequency (E=h*f) and since energy has to be conserved it is the wavelength that must change.

I am sure one can think of a simpler reason, but this is probably as good as any.

Also, remember that -as with everything in physics- this is ultimately an experimental fact, we do know that light travels at different speed in different media, and we also know the if we send in a wave with a given frequency into a medium the wavelength changes whereas the frequency does not.

 

[sphyics]

i was jus trying to picturise the statement
"when light enters from one medium to other its frequency remains same whereas wavelength changes."
http://en.wikipedia.org/wiki/Frequency see the first right hand diagram titled

"Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time."

by using defeniton of wavelength (one crest & one trough) I'm not able to conceptualize the idea of frequency remaining same and wavelength changes.

 

[mikelepore]

The reason the frequency has to be constant when crossing a boundary is because a frequency is a count of individual events, which are, in this case, cycles. It's like if you have birds flying through an open window at a rate of ten per minute, that rate as counted from the outside and that rate as counted from the inside have to be the same.