So my teacher regularly makes mistakes on his powerpoints and this is leaving me feeling uncertain about something he has posted. We are studying the Heisenberg uncertainty principle and discussing a situation in which an electron beam is being fired in the x direction at a small slit (length d) and due to the wave nature of particles some electrons are bending as they leave the slit and have gained momentum in the y direction. so P will denote momentum. P(y) is momentum in the y direction and P(x) is momentum in the x direction. He notes that P(y)/P(x) is equal to the tan of the angle between the vectors. He then notes that because the angle is so small tan θ is roughly equal to the θ and so θ≈P(y)/P(x) Combining this equation with one received earlier from the single slit experiment done by___________: θ=λ/d and so P(y)/P(x)=λ/d So then, this is to represent the max momentum in the y direction of an electron that is diffracted? So the Y component of an electron's momentum ranges P(x)λ/d and -P(x)λ/d Here's where i assume my teacher made a mistake, but i might just be misinterpreting the slide He continuously, for like the next six slides, uses variations of the equation P(x)λ/d∠P(y), which implies the Y momentum is actually always greater than P(x)λ/d? common sense tells me that he messed up on the powerpoint. But the fact that it's written in six different places and the greater than relationship is even expressed in words, has me wondering if I'm missing something. Thanks for the help yall!