Physics (Superposition)

Double Slit

x = λD/a

x = fringe separation

D = distance btwn screen and slit

a = slit separation

Relationships

I proportional to A² (amplitude) proportional to 1/r²

Diffraction Grating

dsinx = nλ

x = angle to 1 maxima(not total angle btwn 2)

d = size of slit

n = order

Total no. of emerging beams from diffraction grating

angle x can be at most 90

x<=90, sinx<=1

d = n x wavelength

total no. = 2n + 1(middle)

Factors affecting diffraction grating

Intensity increase

• diffraction maxima brighter

Separation

• depends only on wavelength and

Total no. of bright fringes visible

2 x nmax + 1

When size of slit become bigger

Single slit

sinx = λ/d

d increase, angle x decrease

intensity increase, central bright maximum become brighter and narrower

Double slit

1. Nothing changes bc separation btwn slit is same OR

2. Fringes no longer observed as slits too wide

Intensity of light increase

Single slit and Double slit

I proportional to A²

Fringes and Peaks become brigher

Reduce the light intensity in 1 of the slits during double slit

Bright fringes become dimmer

Darker fringes become brigher

G X U I M R

2 Sources Coherent

Well-formed interference pattern obtained

Why maxima of interference pattern not all same intensity

Higher order diffracted light has lower intensity compared to lower orders because

Intensity of interference pattern on screen is modulated by a diffraction envelope

Rayleigh’s Criteria

xmin (rad) = lamdar/aperture