TOPIC 11 – WAVE PHENOMENA11.1 – STANDING/ STATIONARY WAVES

STANDING WAVESFormation of standing wavesStanding waves are formed when two identical waves meet each other travel in opposite directions.

Wiki – Waves on a string

The result of this is a wave where the peaks simply move up and down but DO NOT PROGRESS.

STANDING VS PROGRESSIVE WAVESStanding Progressive

Amplitude All points on the wave have different amplitudes. The maximum being 2A (at the antinodes) and 0 (at the nodes)

All points on the wave, have the same amplitude

Frequency Oscillate with the same frequency

Oscillate with the same frequency

Wavelength Twice the distance for one node to the next node

Shortest distance between two points that are in phase

Phase All points between one node and the next node are in phase

All points along a wavelength have different phases

Energy Energy is not transmitted by the wave but it does have an energy associated with it.

Energy is transmitted by the wave.

FORMATION OF STANDING WAVES

FORMATION OF WAVES IN CLOSED PIPES

FORMATION OF WAVES IN OPEN PIPES

11.2 DOPPLER EFFECTThe change in pitch of a sound wave due to a change in frequency of the wave is called the Doppler Effect.

It is caused by the relative motion of the SOURCE and the DETECTOR

MOVING SOURCE

MOVING OBSERVER

DOPPLER EFFECT AND EM RADIATIONThe EM spectrum travels at c through a vacuum but if the velocity of the observed EM radiation in a lot smaller than c then we can use the following equation to calculate the change in frequency

For v << c

DOPPLER EFFECT EQUATIONS

USING THE DOPPLER EFFECT!11.2.6 – Outline an example in which the Doppler Effect is used to measure speed.

11.3 DIFFRACTION A more in depth look at diffraction

Huygens’ Principlehttp://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php

DIFFRACTION FROM A SINGLE SLITWhat is the diffraction pattern shown on a screen when a wave is diffracted around a single slit?

EXPLAINING THE DIFFRACTION PATTERN

EXPLAINING THE DIFFRACTION PATTERN

EXPLAINING THE DIFFRACTION PATTERN

EXPLAINING THE DIFFRACTION PATTERN

EXPLAINING THE DIFFRACTION PATTERN

11.4 RESOLUTIONIf two sources sources of light are very close in angle to each other they can sometimes be seen as one light source.

If we can detect that there are two light sources then we say the light sources are resolved

The ability to do this depends on the RAYLEIGH CRITERION

RAYLEIGH CRITERION

RAYLEIGH CRITERIONIf the sources are to be just resolved, then the minimum of one diffraction pattern is located on top of the maximum of the other diffraction pattern.

For a SLIT – the minima was located atFor a CIRCULAR APERTURE -

IMPORTANCE OF RESOLUTIONResearch the importance of resolution in the development of the following technologies

CDs

DVDs

Electron Microscope

Radio Telescopes

INTENSITYDef’n– Power incident on a unit area(simply put – the greater the intensity the brighter the light will be)

Intensity = Power/ Area

Units = ??

IMPORTANT – There is a squared relationship between intensity and amplitude of the waveIntensity is proportional to the amplitude squared

11.5 POLARISATIONIf a wave is restricted to travel in one plane only, we say it is polarised.

Here the wave is forced to travel in the vertical direction. It can pass through the first slit but cannot pass through the horizontal slit. We say it is polarised in the vertical plane.

Looking at this… Can all types waves be polarised?

EFFECT OF POLARISERS ON INTENSITYPolarisation Sim on wiki

If unpolarised light passes through a set of polarising filters what is the effect on the intensity of the transmitted wave?

MALUS LAW

Key Words – Polariser and Analyser

MALUS’ LAW

MALUS’ LAW

Remember the importance of the squared proportionality relationship between Intensity and Amplitude

POLARISATION BY REFLECTION

When light is reflected from a surface, the reflected ray becomes polarised in the plane of the surface.

The amount of polarisation depends on the angle of incidence.

100% polarisation occurs when the angle of incidence is equal to the Brewster’s angle.

BREWSTER’S ANGLE

BREWSTER’S ANGLE

OPTICALLY ACTIVE SUBSTANCESOptically active substances rotate the plane of polarisation of the light passing through them.

Examples include – sugar solutions, some plastics (when stressed)

With sugar solutions the concentration of the solution changes the amount of rotation. This can be used to determine the concentration on solutions

http://www.chemguide.co.uk/basicorg/isomerism/polarised.html

OPTICALLY ACTIVE SUBSTANCES

USES OF POLARISATION

• Polaroid Sunglasses

• LCD screens

• Stress Analysis

PROBLEMSQuestions 28-31 in your textbook!