[ul] [li]Diffraction is when a wave passesa through a gap or object, and it spreads[/li] [li]For maximum diffraction to occur, the wavelength of the wave must equal or be roughly the same size as the gap ([lambda] = gap-size)[/li] [li]The wavelength of laser red light is [b]630nm[/b], or 6.3[multiply]10^-7[/li] [li]Plane wave fronts are equally spaced and travelling at the same speed[/li] [/ul] [b]Plane wavefronts:[/b] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488032966/plane_wavefronts_pdw6t1.svg'] These wavefronts then become circular when they pass through a gap roughly the same size as their wavelength: [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488033575/diffraction_example_ok6udj.svg'] This is called [b]diffraction[/b]. In the above example, they diffract a lot. In the below example they just reflect, as the gap isn't large enough: [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488035447/ezgif.com-resize_juodfl.gif'] In the below example the gap is a bit bigger, so not much diffraction occurs: [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1488035821/diffraction_example_ray2_idmmti.svg']