waves

Question 1

how is a stationary wave formed

Answer 1

a wave is reflected causing 2 waves to travel in opposite directions with the same speed, frequency, and similar amplitude. a resultant wave is produced as a result of when the 2 waves superposition. total constructive interference at anti-nodes, maximum displacement. total deconstructive interference at nodes, minimum displacement

Question 2

do stationary (standing) waves transfer or store energy

Answer 2

store energy. no energy is transferred

Question 3

are stationary (standing) waves in phase or out of phase

Answer 3

in phase

Question 4

real life applications of standing (stationary) waves?

Answer 4

musical instruments - formation of harmonics
telecommunications - used in antennas to maximise signal strength and minimise interference
medical imaging - used in ultrasound for images of internal organs

Question 5

define coherence

Answer 5

sources are coherent if they maintain a fixed phase difference

Question 6

define progressive wave

Answer 6

transmits energy

Question 7

what is a critical angle

Answer 7

the angle of incidence causing the angle of refraction to be 90

Question 8

what is total internal reflection

Answer 8

occurs inside a medium when a ray reflects back in
happens when angle of incidence larger than critical angle

Question 9

what do fibre optics do

Answer 9

transmit information via light signals and total internal reflection

Question 10

what are fibre optics made of

Answer 10

a core surrounded by cladding
made of glass or plastic

Question 11

what does cladding in fibre optics do

Answer 11

protect the core from damage
prevents signal degradation = light escaping causing information to be lost

Question 12

example of transverse wave

Answer 12

all electromagnetic
string
water

Question 13

example of longitudinal wave

Answer 13

sound
ultrasound

Question 14

what is signal degradation

Answer 14

when light escapes the optical fibre causing loss of information

Question 15

causes of signal degradation

Answer 15

absorption
dispersion

Question 16

what is absorption in an optical fibre

Answer 16

when some energy from the signal is absorbed by the fibre, decreasing its amplitude, losing some information

Question 17

what is dispersion in an optical fibre

Answer 17

dispersion causes pulse broadening which is when the received signal is broader than the original transmitted signal
broader signals can overlap so lose information

Question 18

what are the 2 types of dispersion

Answer 18

modal dispersion
material dispersion

Question 19

what is modal dispersion

Answer 19

when the light rays enter at different angles, so different paths, so different times to travel, causing pulse broadening

Question 20

what is material dispersion

Answer 20

when light rays are of different wavelengths, so different times to travel, causing pulse broadening

Question 21

how can modal dispersion be reduced

Answer 21

have the core of the fibre narrower so less difference between path taken

Question 22

how can material dispersion be prevented

Answer 22

use monochromatic light (light of one wavelength)

Question 23

how can both material and modal dispersion be reduced

Answer 23

use an optical fibre repeater
it regenerates the signal during travel

Question 24

define longitudinal waves

Answer 24

oscillations are parallel to the direction of energy transfer
made of compressions and rarefactions

Question 25

define transverse waves

Answer 25

oscillations are perpendicular to the direction of energy transfer

Question 26

what is a polarised wave

Answer 26

a wave that has oscillations that only travel in one plane only transverse waves can be polarised

Question 27

how to be safe when using a laser

Answer 27

dont shine at person dont shine at reflective materials wear laser safety goggles display warning sign

Question 28

what is the path difference of two waves when constructive interference occurs

Answer 28

nλ where n is an integer

Question 29

what is the path difference of 2 waves when destructive interference occurs

Answer 29

n+1/2 λ where n is an integer

Question 30

what is a diffraction grating

Answer 30

slide which has hundreds of slits per millimetre

Question 31

uses of a diffraction grating

Answer 31

x-ray crystallography finding elements in stars

Question 32

how can the width of the central maxima in an interference pattern be changed

Answer 32

slit seperation wavelength of light

Question 33

what does increasing slit separation do

Answer 33

decrease amount of diffraction that occurs, so make central maximum narrower and increase intensity

Question 34

what does increasing wavelength do

Answer 34

increase amount of diffraction that occurs because wavelength closer to size of slit, make central maximum wider and decrease intensity

Question 35

what does the interference pattern of white light look like

Answer 35

central maximum is white, with alternating light and dark besides it violet is closest to the central maximum red is furthest away from the central maximum because longest wavelength so diffracts more

Question 36

what experiment proves the wave nature of light

Answer 36

young's double slit experiment

Question 37

how fast do electromagnetic waves travel in a vacuum

Answer 37

3x10^8 m/s

Question 38

lasers produce c___ and m____ light

Answer 38

coherent and monochromatic

Question 39

what does coherent light mean

Answer 39

same frequency, wavelength, phase difference