Sandy asked in Science & MathematicsPhysics · 7 months ago

Wavelength vs. Frequency?

Since white light is made up of all of the rainbow colors, when it enters a prism and the light bends, the white light spreads out into the different colors of the rainbow, which is of course known as dispersion.

My confusion is this:

When the light wave goes from one medium to another, the frequency of the wave remains UNCHANGED. However, the wavelength CHANGES, causing the wave to change speed as it moves from one medium to another. The larger wavelengths have a greater speed (red and orange), and the smaller wavelengths have a lower speed (blue and violet). Since they have different speeds through the prism, they bend by different amounts as they exit the prism.

To sum up my question: Doesn't the SAME wave in the spectrum have to have the SAME FREQUENCY, and therefore the SAME WAVELENGTH? For example, as the spectrum below indicates, Red has one single wavelength with its corresponding frequency. So how can you reconcile this with an UNCHANGED frequency but a CHANGED wavelength? That won't be Red anymore! Would it?

What am I missing/misunderstanding here?

Can't wrap my head around this at all!

Thanks for your help!

Attachment image

8 Answers

  • D g
    Lv 7
    7 months ago

    you are not seeing the light  inside the  other medium 

    you see the light after it has LEFT  the medium and come back into our  medium of air..

    the  white light goes in  and each frequency bends at slightly different amounts  based on its frequency ..

    then when it reaches the other side of the  prism it is  bent  so far that  when it comes back into our medium it only bends a TINY  bit back  and does NOT  completely go back to the original place it was before  when it entered 

    it is now  far separate from the other colors so it makes an individual color   of each colour 

    you must also know that  say you are in water 

    and you look at a red light shining into the water  you will see red  because the wavelength   has a relationship with   C to produce  a  energy of a certain frequency

    you do not perceive wavelength  you  perceive the effect the light has hitting the cell in your eye ... and I think this  has  to do with  energy   and frequency  

    if the change in wavelength is great enough the color of the light  does change this is what is called  red shifting or  blue shifting  ..  similar to doppler shift with sound  the  light we perceive can be changed because the speed of the object is so large that it moves from one color to the next in the  color chart

  • Steven
    Lv 7
    7 months ago

    The speed of light is slower in the glass so parallel rays have to travel more perpendicular to the surface of the glass in order to remain in phase, ie the phase difference between two points on the glass surface remains the same inside and outside.  The wavelength is smaller inside the glass. The color is a function of frequency and each color is a range of frequencies, not a single frequency.

  • goring
    Lv 6
    7 months ago

    Color is a function of Power of light radiation,the higher the frequency to more Power. Ultra violet light shows more power than light in the red spectrum.

    Solids indicate a continuous spectrum. we must burn a solid in order to get discrete frequency.

    Hence solids reflect different frequency which we see as a color.Different materials different colors.All gases indicate a discrete spectrum.The human eye can only detect certain frequency.  Animals are able to detect infra red and ultraviolet light.When light goes thru the gases of the atmosphere it cause the sky to fluoresce as blue and at night a very dark blue.Light slows down while moving inside a medium of  glass prism and exists at its normal speed.Hence at different mediums the light speed changes.Wavelength is really the spacing  for each string of photons which indicates how many particle of light in the radiation ray.

  • Zirp
    Lv 7
    7 months ago

    What am I missing/misunderstanding here?

    light that comes from air or vacuum and goes into a prism of glass will suddenly have a lower speed. Frequency stays the same, frequency times wavelength still equals speed, so wavelength is down

    red light gets slowed down more than blue light

  • How do you think about the answers? You can sign in to vote the answer.
  • 7 months ago

    Color is determined by frequency only (frequency determines energy determines which molecules in your retina are brought to an excited state).

    Wavelength depends on frequency and wavespeed but does not determine color, so it can change without affecting color.

  • 7 months ago

    What you are missing  is The speed of light IS NOT CONSTANT. Each color has a RANGE of wavelengths and frequencies and is bent at different angle which changes the speeds of light and red shifts the range of wavelengths for each color.

    White light going into a prism has different wavelengths and frequencies, each color is refracted at a different angle and each color has a different speed. The the frequencies do not change but the wavelengths become longer and the speeds become slower. What you are missing is each color is bent at a different angle AND has a RANGE of wavelengths and frequencies, not a single wavelength and frequency. Some of the red light goes into the short infrared wavelengths and frequencies. The speeds become Lowe and different for each range of frequencies bent at slightly different angles.

    Triclinic minerals can have three indices of refraction. There are seven different atomic lattices.

    Just because humans can't see infrared or ultraviolet doesn't man it doesn't exist. Cats and dogs see further into the infrared than humans. Bees and other insects see ultraviolet light. Humans are blind to most of the electromagnetic spectrum. It's like we are deaf and can hear only one octave of sound.   

  • Anonymous
    7 months ago

    Since in a vacuum (which is what that spectrum is based on though it's not stated), the speed of light is fixed.  A change in wavelength, necessary for different colors means a change in frequency.

  • Jon
    Lv 6
    7 months ago

    What you're missing is that charts such as this are meant to describe the relationship of wavelength and frequency for light in a vacuum, or in a particular medium. They're not meant to describe all possible relationships between frequency and wavelength.

Still have questions? Get your answers by asking now.