quantum mechanics - In double slit experiment how do we observe electrons near slit?

If we observe the electron near the slit, does it produces two bands instead of interference pattern. Also how do we observe electron. Is it by producing electric field. Also does double slit experiment only works with coherent sources of light or all sources? What do you think about the below explanation of wave. http://www.bioinsilico.blogspot.in/2015/03/intelligence-and-in-search-of.html In the figure, the length of up and down represents amplitude and the speed of up and down represents wavelength. If we are observing electrons by producing electric field, won't it disturb the wave nature of electrons.