waves

which type of wave can be polarised, transverse or longitudinal?

transverse

principle of superposition

when two waves of the same type overlap, the displacement is the sum of the two separate displacements

phase

fraction/proportion of the wave cycle completed in comparison to the starting point, usually expressed as an angle

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delete

if phase difference is pi rad/180 degrees, the two points on the same wave are in

antiphase

explain why the core in an optical fibre is made as narrow as possible

to reduce multipath or multimode dispersion

(which would cause) light travelling at different angles to arrive at different times/pulse broadening/merging of adjacent pulses/‘smearing’/ poor resolution/lower transmission rate/lower bandwidth/less distance between regenerators

or to prevent light/data/signal loss (from core or fibre)

(which would cause) signal to get weaker/attenuation/crossover/data to be less secure

which characteristics of monochromatic light change when the light passes from air into glass?

speed and wavelength

define polarisation

The restriction of a wave so that it can only oscillate in a single plane. This can only occur for transverse waves.

The sound quality of a portable radio is improved by adjusting the orientation of the aerial, why?

The radio waves from the transmitter are polarised.

if phase difference is 0 or 2pi rad/360 degrees the two points on the same wave are in

phase

phase difference/2pi =

distance between points on the wave/wavelength

when waves are reflected off a surface they are out of phase with the original wave by

pi rad/180 degrees

what are standing/stationary waves caused by

the superposition of two progressive waves of equal frequency and amplitude moving in opposite directions

how many sources do there have to be to form a standing/stationary wave

can either be two different sources or a wave being reflected back on itself

what are points of 0 amplitude on a stationary wave called

nodes

do progressive waves transfer or store energy

transfer

do standing waves transfer or store energy

store

the displacement of a point on progressive waves varies between peaks and troughs, so amplitude is

the same for each point

the amplitude for a point on a standing wave

varies between 0 (nodes) and a maximum (antinodes)

any point between a and b have phase difference of

0

any point between a and b has a phase difference with a point between b and c of

pi

for fundamental harmonic, length of string =

½ wavelength

define harmonic

overtones that have frequencies that are a whole number of the fundamental frequency are called harmonics

at the point of overlap of two waves if they have the same sign displacement (both + or - ), what type of interference occurs

constructive

at the point of overlap of two waves if one has + displacement and the other -, what type of interference occurs

destructive

constructive interference occurs when the path difference between coherent sources is

a whole number of wavelengths

define coherent

sources have a constant phase relationship and same frequency

describe a diffraction grating

a plate with many, closely spaced, parallel slits

interference pattern from diffraction grating compared with from a double slit arrangement

diffraction grating - brighter and sharper fringes, more rays of light reinforcing the pattern

can calculate wavelength more accurately

describe a progressive wave

transfers energy without transferring material, is made up of particles of a medium that are oscillating

describe superposition

the displacements of two waves are combined as they pass each other, the resultant displacement is the vector sum of each wave’s displacement

do stationary waves transfer energy?

no

how does using white light for a double slit experiment compare with using monochromatic light

central white fringe

alternating bright fringes contain a spectrum

violet is closest to the central fringe and red is furthest

less intense diffraction pattern

wider maxima

what does the double slit experiment tell us about light, and how?

light is a wave

diffraction and interference are wave properties

what is diffraction?

spreading out of waves when they pass through or around a gap of similar size to the wavelength

when is there the most diffraction

when gap size = wavelength

what happens when the gap is larger than the wavelength

less diffraction

what happens when the gap is smaller than the wavelength

most waves are reflected

what happens when a wave meets an obstacle

it diffracts round the edges

what does a wider obstacle (in comparison to the wavelength of the light) mean?

there is less diffraction

what effect does increasing the slit width have in a single slit arrangement?

less diffraction

central maximum becomes narrower and more intense

what effect does increasing the wavelength have in a single slit arrangement?

more diffraction as the slit is closer in size to the wavelength

central maximum becomes wider and less intense

use of diffraction gratings

light from stars is split up to show which elements are present

what is modal dispersion?

light rays enter the fibre at many different angles

many different paths = different lengths of time to travel down the fibre

pulse broadening

what is material dispersion?

light with different wavelengths travel at different speeds

different lengths of time to travel down the fibre

how to prevent modal dispersion

use a narrower core

larger critical angle

how to prevent material dispersion

use monochromatic light

when does refraction occur?

when a wave travels across a boundary between different media and changes speed

purpose of cladding in optical fibres

protection

restricts the amount of total internal reflection, reduces pulse broadening

prevents cross-talk (light going into another core next to it)