L3 waves - diffraction

diffraction

when waves move past a boundary they bend around it. Large wavelengths bend more than short wavelengths

antinodal lines (maxima)

lines of constructive interference

peaks meet peaks, troughs meet throughs

amplitudes add to new amplitude

n = whole number

Nodal lines (minima)

lines of destructive interference

peaks meet troughs

amplitude cancel

n = something .5

path difference

the difference in the distance between a selected point and each of the sources. it is usually expresses as a multiple of wavelength.

path difference in relation to nodal and antinodal lines

Where the path difference is a whole number of wavelengths there is an antinodal line. where the path difference in something .5 wavelengths, there is a nodal line.

d

split separation (m)

x

vertical distance (m)

L

screen distance (m)

n

order number

what does more slits mean

narrower because more sources are interfering causing destructive interference. brighter because more sources contribute to points of constructive interference.

light

when white light is viewed through a diffraction grating, longer wavelengths appear at a large angle. this occurs because longer wavelengths have a longer path difference

secondary maxima  (consider a 3 source interference pattern)

maxima occur when all 3 sources meet in phase. with 3 sources however, we also have regions where 2 out of the 3 sources meet in phase, these regions form smaller secondary maxima