cool

1. Diffraction
S M Ali Shah

2. Diffraction
• The bending of light around an obstacle and
spreading of light wave into the geometrical
shadow of an obstacle.

3. Condition for diffraction :
• The condition for diffraction of light is that the
size of slit or opening must be comparable to
the wavelength of light.

4. Single slit diffraction :
• Consider the narrow slit AB of width ‘d’ which
is illuminated parallel rays of monochromatic
light of wavelength ‘λ’ .
• The screen S is place parallel to slit, to
observe the diffraction of light .
• On passing through slit the light rays are
diffracted at angle θ

5. Single slit diffraction :

6. Single slit diffraction:

7. Single slit diffraction :
• The small portion of incident wave fronts
which passes through the narrow slit each
point on this portion of wave fronts send out
secondary wave fronts.
• These wave fronts are in phase , which on
interaction produces diffraction pattern on the
screen.

8. Single slit diffraction :
• We consider only 5 rays as A, X, Q, Y and B.
• The wavelets from all these points on screen
have a path difference equal to zero , on point
O produces constructive interference so that
point O is bright.

9. Single slit diffraction :
Below point ‘O’ on the screen there is a point
‘P’ ,the path difference between the wavelets
which sent out by A & Q to point P on the
screen is half wavelength which produces
darkness and dark fringe is observed.
• From point Q draw a perpendicular QM on ray
of light where AM give the path difference ‘S’.