hi prof!

can make your ejs applet to allow to show this?

A wave spreads out (noticeable diffraction) when the size of the slit is comparable to or smaller than the wavelength.

When waves reach a narrow slit, the water in the slit vibrates like a point source. The waves thus sent out from secondary sources along the slit are nearly in-phase when arriving any point in the forward direction. The diffracted wave resembles a circular wave with centre at the slit.
currently i think the ejs applet above only shows a circular source (i change it to n=1) at the slit width that spread in 180 degree which will occur when wavelength ~= slit width, that should be a lesser wave at the sides.[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=2082.0;attach=3837;image[/img] i made slidth width = wavelength = 0.5, is should show lesser waves (represented perhaps by less intensity?) at the sides

A wave goes straight when the size of the slit is much larger than the wavelength.
currently i think the ejs applet above does not show this effect when wavelength << slit width[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=2082.0;attach=3839;image[/img]