- #1
hokusai
- 4
- 0
Light as a "wave"? Of what?
If I watch waves traveling through water (say, a pond) I can see that the actual water molecules are moving, transversely to the direction of the wave; To put it simply, a given water molecule will be closer to the bottom of the pond at a wave-trough than at a wave peak. The distance between peaks (or troughs) gives the 'frequency' of the wave, and the distance between a molecule's position at a peak and at a trough gives its amplitude.
Am I right so far?
Similarly, 'if I 'observe' a sound wave (in air) , I shall find that air molecules are more closely compressed, hence bunched together, at some times (the 'peaks') than at the troughs; the sound wave is thus a compression, or fore-and-aft, wave. Yes?
The 'direction of motion' of such a wave -- the way it spreads across a pond, for instance -- doesn't in fact imply the physical movement of anything in the direction of the wave. But, none the less, something is moving, transversely to, or fore-and-aft with respect to, the wave, and the movement of those 'somethings' -- water molecules, air molecules, or whatever -- can be observed with respect to their movement.
My question is this :- What is it that is moving in the case of a light wave? The wave, too, has a frequency (which, over some range, determines its 'colour') and an amplitude, which determines its brightness. And, since light can be polarised, we can determine 'the transverse direction of its amplitude' (if you see what I mean).
But WHAT is it that is moving transversely to its direction of propagation?
And, if the answer is "Nothing" -- then what do we mean by saying that light has -- or, at least, can sometimes have -- the attributes of a wave ?
Martin Woodhouse [ http://www.martin-woodhouse.co.uk ]
If I watch waves traveling through water (say, a pond) I can see that the actual water molecules are moving, transversely to the direction of the wave; To put it simply, a given water molecule will be closer to the bottom of the pond at a wave-trough than at a wave peak. The distance between peaks (or troughs) gives the 'frequency' of the wave, and the distance between a molecule's position at a peak and at a trough gives its amplitude.
Am I right so far?
Similarly, 'if I 'observe' a sound wave (in air) , I shall find that air molecules are more closely compressed, hence bunched together, at some times (the 'peaks') than at the troughs; the sound wave is thus a compression, or fore-and-aft, wave. Yes?
The 'direction of motion' of such a wave -- the way it spreads across a pond, for instance -- doesn't in fact imply the physical movement of anything in the direction of the wave. But, none the less, something is moving, transversely to, or fore-and-aft with respect to, the wave, and the movement of those 'somethings' -- water molecules, air molecules, or whatever -- can be observed with respect to their movement.
My question is this :- What is it that is moving in the case of a light wave? The wave, too, has a frequency (which, over some range, determines its 'colour') and an amplitude, which determines its brightness. And, since light can be polarised, we can determine 'the transverse direction of its amplitude' (if you see what I mean).
But WHAT is it that is moving transversely to its direction of propagation?
And, if the answer is "Nothing" -- then what do we mean by saying that light has -- or, at least, can sometimes have -- the attributes of a wave ?
Martin Woodhouse [ http://www.martin-woodhouse.co.uk ]