Fringe Spacing!?

Hello, Just what exactly is the fringe spacing, distance between two consecutive first order maximas or distance between two cosecutive minima's ?

Thanks a lot
From John

Reply 1

phys981

10

two consecutive first order max?

There aren´t consecutive first order max

There is a zero order, with a first order on either side, then a 2nd order.

But yes, you can measure fringe spacing between consecutive max.

Out of interest are you talking grating or two-slit?

Reply 2

F1 fanatic

16

Neo1

Hello, Just what exactly is the fringe spacing, distance between two consecutive first order maximas or distance between two cosecutive minima's ?

Thanks a lot
From John

It doesn't matter I don't think. As long as you take the distance between 2 consecutive maxima or 2 consecutive minima it should be the same. The standard definition is the distance between 2 consecutive maxima, as rsk says :smile:

It also doesn't make any difference whether it is 2 slit or grating (though the answer is different, the principle is the same), the 2 slit is just a specialisation of the N slit grating :smile:

Reply 3

phys981

10

F1 fanatic

It also doesn't make any difference whether it is 2 slit or grating (though the answer is different, the principle is the same), the 2 slit is just a specialisation of the N slit grating :smile:

In theory, no, but the reason I ask is because I think for a standard grating you get much more widely spaced bright spots, so measuring the distance between minima would be tricky as you´d have to estimate where was the centre of the minima.

With the usual 2-slit stuff the fringes are much closer and you could do it more easily.

Reply 4

F1 fanatic

16

rsk

In theory, no, but the reason I ask is because I think for a standard grating you get much more widely spaced bright spots, so measuring the distance between minima would be tricky as you´d have to estimate where was the centre of the minima.

With the usual 2-slit stuff the fringes are much closer and you could do it more easily.

yes, this is true, for a grating you have principal maxima, peaks which are particularly reinforced. In both cases though, as you say, you take the distance between maxima generally, as it is easier to carry out experimentally. In theory though you could do either, in practice you do whichever is easier to measure more accurately.

In some instances it is actually easier to measure the minima, as it is much easier to judge when something is dark than when it is maximally bright, particularly if you have a single slit diffraction pattern for example.

Fringe Spacing!?

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