Polarization, Diffraction and Interference

Behavior of Waves

Essential Knowledge 6.A.1: Waves can propagate via different oscillation modes such as transverse and longitudinal.a. Mechanical waves can be either transverse or longitudinal. Examples should include waves on a stretched string and sound waves.b. Electromagnetic waves are transverse waves.c. Transverse waves may be polarized.

Polarization

• Polarization is the preferential orientation of the electromagnetic field vectors of light, and is evidence that light is a transverse wave.

• A transverse wave is polarized if its vibrations are in a single plane.

Diffraction

Essential Knowledge 6.C.2: When waves pass through an opening whose dimensions are comparable to the wavelength, a diffraction pattern can be observed.

Diffraction

Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings

Superposition ..AKA….InterferenceOne of the characteristics of a WAVE is the ability to

undergo INTERFERENCE. There are TWO types.

We call these waves IN PHASE.

We call these waves OUT OF PHASE.

Young’s double slit experiment

The interference pattern

Analytical Methods for Fringes

y

d sin qs1

s2

dq

p1

p2

Bright fringes: d sin q = ml, m = 0, 1, 2, 3, . . .

DL = p1 – p2 = md sin = q m

Path difference determines light and dark pattern.

x

InterferenceIf light waves strike two narrow, closely spaced slits, the circular wavelets leaving each slit on the other side interfere constructively at some places to form bright bands of light and destructively at other places to form no light. The angular deflection of rays moving in the direction of bright bands is determined using the equation

d sin = q m for m = 0, 1, 2,…where d = slit separation = wavelength of the light m = order of the bright band (zero for central maximum, 1 for the first bands on each side, and so on)