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question dude
Feb24-13, 07:02 PM
P: 77
Quote Quote by Philip Wood View Post
Your understanding is correct. I think your textbook diagram is confusing, and partly wrong. I'll explain.

I think the dotted red line is supposed to represent a two source pattern with no superimposed diffraction effects. It is wrong because (1) it omits the central fringe (2) it makes the bright fringes too sharp. The intensity should follow a 'cos squared' graph, which is sinusoidal in shape. This implies that at mid-intensity (halfway up the vertical axis) the widths of bright and dark fringes should be equal. They don't seem to be.
sorry I don't quite understand what this is

Quote Quote by Philip Wood View Post
The red solid line is the single slit diffraction pattern for a slit with a width of 2s, in which s is the distance between the slit centres used for the two slit graph.
how comes the solid red line is not a double slit diffraction pattern?

because thats what it appears me. There are three fringes from that solid red line occupying the space inside a wide central fringe (from the blue line)

Quote Quote by Philip Wood View Post
I find this confusing, because slits of this width couldn't have a separation s between their centres without merging into one wide slit.
I didn't notice this until you've point it out here. Yeah that is impossible, the distance between the two slit centre must to be greater than the slit width. It makes no sense.