3 Waves

Question 1

what do waves do

Answer 1

transfer energy from one place to another without transferring matter

Question 2

what is frequency

Answer 2

the number of oscillations (vibrations) per second

Question 3

what is period (of oscillation)

Answer 3

the time taken to complete one oscillation

Question 4

what is amplitude

Answer 4

the largest distance that a point on the wave moves from its rest position

Question 5

what is wavelength

Answer 5

the distance between two adjacent wavefronts

Question 6

what is the phase of a wave

Answer 6

describes how far through a cycle the wave is

Question 7

what is phase difference

Answer 7

a measure of the difference in where two waves are in their cycle

Question 8

what are transverse waves

Answer 8

causes particles in the medium to vibrate at right angles to the direction of wave motion

Question 9

what are longitudinal waves

Answer 9

causes the medium’s particles to vibrate in the same direction as the wave’s motion

Question 10

what is polarised light

Answer 10

polarised light can only travel in one direction

Question 11

what waves can be polarised

Answer 11

transverse

Question 12

what are some applications of polarisation

Answer 12

sunglasses, television transmission and reception

Question 13

how are stationary waves formed

Answer 13

when two progressive waves, each with the same frequency and wavelength, and moving in opposite directions, interfere with each other.
this creates a wave which doesn’t transfer energy from one place to another.

Question 14

what are nodes

Answer 14

points on a stationary wave that have zero amplitude

Question 15

what are antinodes

Answer 15

points on a stationary wave with maximum amplitude

Question 16

what are resonant frequencies

Answer 16

stationary waves can only have certain frequencies - these frequencies = resonant frequencies

Question 17

when will resonant frequencies happen

Answer 17

when the distance between the two fixed ends in an integer multiple of half wavelengths, ½λ

Question 18

what is the first harmonic

Answer 18

the first resonant frequency
happens when the distance between the two fixed ends is exactly ½λ
(has 2 nodes and 1 antinode)
= fundamental frequency

Question 19

what is the relationship between length and frequency

Answer 19

the longer the length of the string the lower the frequency
this is because the longer the length is the longer the half wavelength must be so the lower the frequency

Question 20

what is the relationship between the mass per unit length and frequency

Answer 20

the larger the mass per unit length the lower the resonant frequency
for the same length of string, waves travel more slowly a through a heavier string, so the frequency must be lower

Question 21

what is the relationship between tension and frequency

Answer 21

the higher the tension in a string the higher the frequency
this is because waves travel more quickly down a string with higher tension

Question 22

what does coherent mean

Answer 22

coherent means that the two waves must have the same frequency and wavelength and have a fixed phase relation (usually 0)

Question 23

when does interference happen

Answer 23

when any two waves are superimposed on one another

Question 24

what is path difference

Answer 24

the difference in length travelled by the waves to get to a certain point

Question 25

what happens when the path difference is a multiple of ⋋

Answer 25

the waves will be in phase and we will see constructive interference

Question 26

what happens when the path difference is a whole number plus half a ⋋

Answer 26

the waves will be exactly out of phase and we will see destructive interference

Question 27

what does monochromatic mean

Answer 27

all light is of the same wavelength

Question 28

what is Young’s Double Split experiment

Answer 28

deals with the interference from two monochromatic coherent sources

Question 29

what is single slit diffraction

Answer 29

when a light is shone though a single slit it diffracts and produces a distinct pattern
(if the wavelength of the light is roughly the same as the width of the single slit)

Question 30

what does constructive interference cause in single slit diffractions

Answer 30

bright fringes

Question 31

what do destructive interference cause in single slit diffraction

Answer 31

dark fringes

Question 32

what happens if the slits width increases

Answer 32

width of central maximum decreases and its intensity increases (because they are less spread out)

Question 33

what happens to the central maximum if the wavelength increases

Answer 33

width of central maximum will increase and its intensity will decrease (because photons are more spread out)

Question 34

what is refraction

Answer 34

when light changes speed and bends when it passes from one medium to the next

Question 35

what is Snell’s law

Answer 35

relates refractive indices to the angles of incidence and refraction
n1 sinθ1 = n2 sinθ2

Question 36

how does light speed relate to the optical density of the material

Answer 36

the more optically dense a medium is, the slower light travels through it, and therefore the larger its refractive index

Question 37

what is total internal reflection

Answer 37

at angles of incidence larger than or equal to the critical angle, no light is refracted, instead all of the light is reflected

Question 38

what are optical fibres

Answer 38

they transmit light by total internal reflection

Question 39

what is cladding

Answer 39

each fibre has a core of optically dense material that is covered by a layer of cladding with a much lower optical density
this means that the boundary between the two materials has a very small critical angle

Question 40

what is pulse broadening

Answer 40

caused by both material and modal dispersion
the pulses emerging from the fibre are longer than those entering

Question 41

how is diffraction different for red and blue light

Answer 41

Red light has a longer wavelength so diffracts more than blue light
The central maxima is a bright white light