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How to understand wavelength in a simple way

  1. Mar 14, 2016 #1
    Guys, i"m only 13 and i somehow got curious in astronomy. I want to know how wavelength works in a simple way. Please help me guys :P
  2. jcsd
  3. Mar 14, 2016 #2


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    Think of a set of waves out in the ocean. It's just a series of parallel ridges and troughs. The wavelength is the distance from one peak to the next - which is the same as the difference from one trough to the next.
    Now think of a sound wave. This is a series of variations in air pressure between the source and the listener. If you draw a straight line from the source to the listener and measure the air pressure everywhere along that line at an instant in time, the pressure will vary as you move along the line, approximately like a sine wave. The wavelength is the distance from one pressure peak of that wave (a point of locally maximum air pressure) to the next.
    Now for astronomy, the waves are electromagnetic radiation, which are variations in electric and magnetic fields, rather than air pressure or water height. If you draw a straight line between the distant star and the observer on Earth, and measure the electric field at all points along that line, its magnitude will vary along the line, again like a sine wave. Again, the wavelength is the distance along the line from one point of local maximum in electrical field to the next.
    There are complications to that, involving issues like coherence, polarization and red-shift. But for a simple explanation, I think the above covers the main issues without being too oversimplified.
  4. Mar 14, 2016 #3
    It's literally just the length of a wave.
  5. Mar 14, 2016 #4


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    You know what a sine wave is from math?
  6. Mar 14, 2016 #5


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    That's an incredibly vague answer :wink:
  7. Mar 16, 2016 #6


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  8. Mar 16, 2016 #7


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    Wavelength is a property of waves. So you need to understand waves a bit.
    Though you're interested in light, I don't think that's a good place to start, as those waves are not obvious. Even sound has the same problem.

    I'd play around with ripples in water (chuck a rock in a pond or dabble your finger in a bowl of water), wobbling a skipping rope or washing line, a slinky if you've got one. The easiest waves to understand are when you wobble things at a fixed rate (frequency), which gives a fixed wavelength. Look at how things move, both overall and a single part and what a wave looks like in different places and at different times. You can make models, like a wave pattern drawn on paper and pulled behind a thin slit, or a helix drawn on a tube and look at it sideways while rotating it.

    Then when you look in books or on the internet, you can relate the diagrams to your experiences and have more chance of understanding what they are saying.
    It's not an easy subject, because waves vary in both time and space (distance) and it's easy to get confused about what aspect is being talked about. You have the advantage over me, when I learnt about this, that you can have moving diagrams on the internet rather than just snapshot line drawings.

    Probably not the sort of help you were seeking, but the essential thing for understanding(IMO) is to have physical experiences that you can relate the pictures and explanations to.
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