3.3- Waves

what is a node on a stationary wave

a point that doesn’t move from equilibrium position

what is an antinode on a stationary wave

a point that experiences maximum displacement from equilibrium position

how can stationary waves be created

two waves of the same frequency travelling in opposite directions

when will a wave diffract through a gap

when the gap is smaller than the wavelength

what does coherent sources mean

same frequency, constant phase relation

describe the interference pattern when white light is used

central white maximum, other maxima are spectrums with violet on the inside/ red on the outside

features of a single slit interference pattern

very intense central maximum that is twice as wide as the subsidiary maxima

how does a longer wavelength affect the fringe spacing

wider fringe spacing

how does a wider slit separation affect the fringe spacing

more compact fringe spacing

how does a further away screen affect the fringe spacing

wider fringe spacing

what colour of light refracts the most and why

red because it has the longest wavelength

applications of diffraction gratings

• spectrometers to analyse composition of stars

• spectrometers to analyse chemicals

• x-ray crystallography

safety procedures when working with lasers

• protective eyewear

• don’t point at people’s eyes

• usage clearly signposted outside the room

when is a ray totally internally reflected

when n₁>n₂ and θ>θc

a substance that has a higher refractive index is…

more optically dense and slows light down more

what are the meanings of the symbols in this equation

• f= frequency

• l= length of wire

• T= tension in wire

• µ= mass per unit length

what is the nth harmonic

when n half wavelengths take up the whole length of the wire

name the three parts of a fibre optics cable (and describe their optical densities if applicable)

• optically dense core

• less optically dense cladding

• outer sheath

function of the core

allows total internal reflection to take place

function of the cladding

• prevents signal degradation (light escaping the core), which causes information to be lost

• prevents crossover of information to other fibres

function of the sheath

prevents damage to the cable

two ways a signal can be distorted

absorption and pulse broadening

consequences of pulse broadening

• reduces amplitude- can lead to loss in information

• different pulses could merge- leading to distorted final pulse

consequence of absorption

reduces amplitude, leading to loss of information

two causes (with brief description) of pulse broadening

• material dispersion- when white light is used the different colours diffract differently so the pulse arrives over a longer period, as some rays take different paths

• modal dispersion- when the light enters the core at different angles, so diffracts along different paths and the pulse arrives over a longer period

how to solve material dispersion

use monochromatic light

how to solve modal dispersion

use a very narrow core, so the range of “entry angles” is as small as possible

polarization means…

oscillations occur in only one of the directions perpendicular to the direction of wave propagation

what type of waves can be polarised

transverse

what happens when two polarising filters are at an angle to each other

maximum intensity at 0, 180, 360 ect, and no rays can pass at 90, 270 etc, inbetween it decreases like a cosine graph

what happens to light when it’s reflected off water

is partially plane polarised on the horizontal plane

how do polaroid sunglasses work

they vertically polarise light, so the horizontally polarised light from a surface (the glare) is reduced