Light as a wave - evidence

What are wave behaviors that are NOT particle behaviors?

• interference – constructive & destructive

• diffraction

Interference pattern from 2 sources.

When 2 or more waves interact, they interfere both constructively

and destructively.

Wavefronts in water

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=hfC13qEqYi3yKM&tbnid=bQmXd9QCZFBLLM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.scienceclarified.com%2FHe-In%2FInterference.html&ei=TlU9U7WsGsPNsQTa9oHgBw&bvm=bv.64125504,d.b2I&psig=AFQjCNHHCSJebEhhtmAM0Gr9mc8fZg7coA&ust=1396614797830370

What is diffraction?

https://www.youtube.com/watch?v=4EDr2YY9lyA

Diffraction = bending around boundary.

Point to the water wave diffraction.

Diffraction around wall or pillar.What’s going on here? What is different?

Diffraction through slits.Curving is greater for opening

that are nearer the .

Double Slit Demo

Interference

• Light rays will undergo superposition and interfere both constructively and destructively.

Interference is a wave behavior!!

Young’s Double Slit Experiment

If you pass coherent light rays through two slits, what will you see on

a screen?

Used Coherent Monochromatic Light Source (laser)

Observed Pattern

Demo here

The observed pattern results from a combination of

diffraction & interference.

It’s like the circular ripples sent from 2 sources, now the 2 sources are the slits.

Nodal & Antinodal lines.

Nodes occur when crests and troughs overlap – canceling each other. Waves are out of phase.

Antinode lines occur when crest overlap with crests or troughs with troughs. Waves are in phase.

Node

Antinode

Young’s Double Slit Experiment

http://en.wikipedia.org/wiki/File:Single_slit_and_double_slit2.jpg

Light shows diffraction, constructive and destructive interference. This is evidence

light is a wave.

Polarization - Light as a transverse wave.

Only transverse waves can be polarized.

Polarization – forced to vibrate in only certain directions.

Light is part of EM spectrumdefined by wavelength.

All waves show all discussed behaviors except polarization. Only transverse waves can be

polarized.

Summary

• Diffraction & Interference indicate light is a wave.

• Polarization indicates light is a transverse wave.

Fringe Pattern

Can measure of laser

= xdnL

Relate distances to wavelength.

= wavelengthd = slit spacingn= order of fringeL = distance btw. Slits & screen

Example:A pair of slits are placed 13.7 m from a screen. A third order fringe is seen on the screen 2.5 cm from the central fringe. If the slits were cut 0.0960 cm apart, determine the wavelength of this light. Roughly what color is it?

584 nm yellow

The intensity drops off from the central maximum. It is apparent for sound & light.

Passing polarized light through another polarizer.

40. OPTICS STREAMING

Huygen’s Principle for DiffractionWavelets that pass through the opening predict position of new fronts.