Double slit experiment doesn't work

[itaybrodsky]

I took a piece of carton and cut out to strands in it. When I shine the line through it, it only projects the two strands on the other side. I tried it with every light in my house but it still didn't work. what do I have to do, to create the wave interference pattern on the other side.
Thank you

 

[mathman]

http://en.wikipedia.org/wiki/Double-slit_experiment

It depends on the width of the slits and the separation.

 

[jtbell]

It's difficult to demonstrate two-slit interference with ordinary light sources because they're incoherent and emit a mixture of wavelengths. Have you tried a laser? A cheap laser-pointer should do the job OK.