Chapter 27 WAVE OPTICS PHYSICAL OPTICS DOUBLE SLIT
Chapter 27 WAVE OPTICS (PHYSICAL OPTICS ) DOUBLE SLIT AND THIN FILM INTERFERENCE
WHAT IS PHYSICAL OPTICS 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.
ADDING WAVES Constructive interference Destructive interference Combining two waves does not always give you a bigger wave!
SHIFT BY HALF A WAVELENGTH Constructive Destructive
CONSTRUCTIVE INTERFERENCE Distance to the left: 2λ Distance to the right: 2λ λ Crests always arrive at the same time as crests Troughs always arrive at the same time as troughs
CONSTRUCTIVE INTERFERENCE Distance to the left: 3λ Distance to the right: 1λ λ Crests always arrive at the same time as crests Troughs always arrive at the same time as troughs
IN GENERAL (CONSTRUCTIVE) Constructive interference occurs whenever the path difference is an integral multiple of λ:
DESTRUCTIVE INTERFERENCE Distance to the left: 2λ Distance to the right: 1. 5λ λ Crests always arrive at the same time as troughs
IN GENERAL (DESTRUCTIVE) Destructive interference occurs whenever the path difference is an half-integral multiple of λ:
THE SAME IS TRUE IN 2 D (CONSTRUCTIVE)
THE SAME IS TRUE IN 2 D (DESTRUCTIVE)
PHASE DIFFERENCE AND PATH DIFFERENCE
INTERFERENCE ON WATER
RIPPLES
IT IS ALL ABOUT PATH DIFFERENCE
YOUNG’S DOUBLE SLIT (1800)
WHAT ARE THE FRINGES? The bright fringes represents regions of high intensity I The dark fringes represents regions of low intensity.
THE MIDDLE Constructive Interference! Why is I high here? Light can reach this place via two paths, r 1 and r 2. Path difference is: r 1 r 2
WHAT ABOUT THE OTHER FRINGES?
BRIGHT AND DARK FRINGES
CALCULATING THE ANGLE
WHAT YOU SEE
EXAMPLE Given λ = 700 nm and d = 3500 nm, find the angles at which you can find the 0 th, 1 st and 2 nd order maxima. What if you double d? (Notation: m = order ) d
RADIO BROADCAST The frequency f =1. 5× 106 Hz, from two antennas shown below. In what directions will you find the strongest signal?
POSITION ON THE SCREEN
POSITION ON THE SCREEN (APPROXIMATION)
POSITION ON THE SCREEN (APPROXIMATION)
FIND THE WAVELENGTH
FIND THE WAVELENGTH
FIND THE WAVELENGTH (ALTERNATIVE)
INTENSITY
WAVELENGTH IN DIFFERENT MEDIUM
WAVELENGTH IN DIFFERENT MATERIALS
EXAMPLE Assuming θ =0°, λ=550 nm, n. Mg. F = 1. 38, what is the smallest L so that the two light rays shown will cancel out each other?
INTERFERENCE AROUND US
SOAP BUBBLES
NEWTON’S RINGS
- Slides: 37
