Interference

Friday, 14 September 2018

1:07 PM

Constructive interference - net amplitude is increased

Destructive interference - net amplitude is decreased

 

Conditions for Interference

• Wave sources must maintain a constant phase in respect to each other
• Waves should be monochromatic (single wavelength)

 

Interference Pattern

From Young's double-slit experiment, the light from the two slits form a visible pattern on a screen, where there are bright and dark fringes.

 

Path Difference

 

For a bright fringe (constructive interference), the path difference must be zero or an integer multiple

 

For a dark fringe (destructive interference), the past difference needs an odd half wavelength

 

Where  is the order number

, zeroth-order maximum

, first-order maximum

 

For ,

When  is small,

 

So then

 

 

 

The phase difference between two waves at a point depend on their path difference,

A path difference of  corresponds to a phase difference of  rad

 

 

So, intensity is

 

Interference pattern consists of equally spaced fringes of equal intensity, iff L>>d,  is small

 

Factors

• Phase reversals on reflection
• Difference in travel distance