Chapter 35

It is the study of light as waves. Geometric optics treats light as particles (or rays) that travels in straight lines. Physical optics (wave optics) deals with the wave nature of light, such as the spreading of waves (diffraction) and the interference of waves.

Combining two waves does not always give you a bigger wave!

Constructive Destructive

 Distance to the left: 2λ Distance to the right: 2λ Crests always arrive at the same time as crests Troughs always arrive at the same time as troughs

 Distance to the left: 3λ Distance to the right: 1λ Crests always arrive at the same time as crests Troughs always arrive at the same time as troughs

path difference integral multiple Constructive interference occurs whenever the path difference is an integral multiple of λ : 

 Distance to the left: 2λ Distance to the right: 1.5λ Crests always arrive at the same time as troughs

path difference half-integral multiple Destructive interference occurs whenever the path difference is an half-integral multiple of λ : 

The bright fringes represents regions of high intensity I The dark fringes represents regions of low intensity.

r1r1 r2r2 Light can reach this place via two paths, r 1 and r 2. Path difference is: Why is I high here?

Given λ = 700nm and d = 3500nm, find the angles at which you can find the 0th, 1st and 2nd order maxima. What if you double d ? (Notation: m = order ) d

The frequency f =1.5×10 6 Hz, from two antennas shown below. In what directions will you find the strongest signal?

No relative phase shift ΔΦ =0 Relative phase shift ΔΦ =π

Assuming θ =0°, λ=550nm, n MgF = 1.38, what is the smallest L so that the two light rays shown will cancel out each other?

Is the fringe at the line of contact bright or dark? Given l=10cm, h=0.02mm and λ=500nm, find the fringe spacing.

What if we change the upper plate to a plastic with n =1.4, and fill the wedge with a grease of n =1.5, while the bottom is a glass with n =1.6 ?