Why does laser light reflected from a diffuse surface appear speckled?

[h0dgey84bc]

When laser light is reflected from a diffuse surface, what is the reason that it appears speckled?

 

[mgb_phys]

Interference - the waves reflected from each point n a rough surface add together to give either bright or dark points dependign on wether there are an odd or even number of wavelenghts between that point and your eye.
You can think of it as thousands of youngs slits experiments on top of each other.

 

[h0dgey84bc]

Thanks for the reply, I just had this question on a test, and the amongst the answer choices were a) because beam is collimated b) beam is coherent...I put collimation of beam, I guess it must be coherence :(