Re: Thomas Young's experiment

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

At 21:48 -0800 10/30/03, Ludwik Kowalski wrote:
> Yes, using sun rays (reflected into a room by a mirror) would
> increase the intensity a lot. But was the real experiment
> performed by using the sun or a flame? That is the question.
> Also was it a set of slits or a set of pinholes?

I couldn't find a reference to answer that definitively. Asimov's
Biographical Encyclopedia says it was slits, but that is not
necessarily an authoritative source, especially on small details like
that. But it does seem that a flame of the type available by the
early 1800s, focused by a concave mirror, would have given sufficient
intensity. Do you have some knowledge that the slits were about 50 cm
from the source hole, or are you guessing? I don't think that
distance would have been necessary, as long as the distance was large
compared to the source hole size. A few cm should have been enough,
and would have increased the final intensity considerably, compared
with a 50 cm distance. And if the two slits were close enough
together, one could be much closer to the slits than a meter, still
further increasing the intensity. So keeping the scale of the
experiment down to about 10 cm instead of 150 cm, could result in an
intensity gain of about a factor of 200, which might be enough to
make the interference pattern visible even in the feeble light of a
candle.

I have demonstrated the effect using a laser on a double slit
arrangement and been able to see the effect quite easily only two or
three cm away from the slits. Of course that isn't much good for
demonstrating it to a class full of students. But ti would be
acceptable if he had only one or two viewers other than himself.

Hugh
--

Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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