Waves

Question 1

What is a progressive wave?

Answer 1

a wave that carries energy from one place to another without transferring matter

Question 2

What is frequency?

Answer 2

the number of oscillations per second

Question 3

what is phase difference?

Answer 3

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

Question 4

what is reflection?

Answer 4

when the wave bounces back when it hits a boundary

Question 5

what is refraction?

Answer 5

when a wave changes direction as it enters a different medium

Question 6

what are transverse waves?
- example?

Answer 6

a wave in which the oscillations are perpendicular to the direction of the energy transfer
-electromagnetic waves

Question 7

what are longitudinal waves?
- example?

Answer 7

a wave where the oscillations are parallel to the direction of energy transfer
- sound waves

Question 8

what is a polarised wave?
- this can only happen to what kind of wave?

Answer 8

wave that only vibrates in one plane
- transverse waves

Question 9

what are applications or polarisers?

Answer 9

sunglasses, television transmission and reception

Question 10

explain how polaroid material works?

Answer 10

polaroid sheets are made of long molecules that run up and down the sheet. waves parallel to the molecules are absorbed and those perpendicular are transmitted.

Question 11

what are stationary waves?

Answer 11

a wave formed when two progressive waves with the same frequency and wavelength are moving in opposite directions and interfere with each other

Question 12

What are nodes?

Answer 12

points on a stationary wave that have zero amplitude

Question 13

what are antinodes?

Answer 13

points on a stationary wave with maximum amplitude

Question 14

what is the equation of the first harmonic?

Answer 14

f= (1/2L) x √( T/μ)

Question 15

what is the principle of superposition?

Answer 15

when two or more waves meet at a point, the resulting displacement at that point is the sum of the individual displacements of each wave

Question 16

what does coherence mean?

Answer 16

when two waves have the same frequency and wavelength and a fixed phase relation

Question 17

what does monochromatic mean?

Answer 17

light of the same wavelength

Question 18

how could you use a laser as a source of monochromatic light?
-what does this produce?

Answer 18

shine laser through two slits and they act like two identical sources of laser light
- a series of light and dark fringes corresponding to constructive or destructive interference

Question 19

what is the equation for fringe spacing in a double slit experiment?

Answer 19

w= λD/s

Question 20

What would the interference pattern look like if white light was used in a double slit experiment?

Answer 20

Bright white middle fringe and side fringes have a spectrum of visible colours, blue is nearer the centre and red further out as blue diffracts less than red.

Question 21

What safety precautions must be taken when handling lasers?

Answer 21

-not point laser in people’s eyes
-wear protective eyewear
-use proper signage so that people understand that you are dealing with lasers

Question 22

How has light been theorised over the years?
newton, huygen, young, einstein

Answer 22

• Newtons corpuscles (packets of light)
• Huygen’s waves (wavefront theory)
• Young’s double slit experiment (backed Huygen)
• Einstein’s photons, photoelectric effect (backed newton)

Question 23

Suggest an experiment on how can we observe interference in sound waves

Answer 23

set up two sound sources (speakers) that play the same sound at the same time, by moving a microphone from one side to the other we can measure constructive and destructive interference by whether the noise is loud or quiet

Question 24

-How is constructive interference shown on a diffraction grating?
-How is destructive interference shown on a diffraction grating?

Answer 24

-bright lines
-dark lines

Question 25

what are orders?

Answer 25

position of maxima

Question 26

what is the zero order?

Answer 26

the largest, brightest line in the middle

Question 27

what happens in the grating as the number of slits increase?

Answer 27

sharper lines

Question 29

what is the diffraction grating equation?

Answer 29

dsinθ=nλ

Question 30

what happens to the diffraction pattern if we : -increase the wavelength? -increase the slit screen distance?

Answer 30

-patterns becomes more spread out -pattern becomes less spread out

Question 31

Why are diffraction gratings useful? a specific example of a use case?

Answer 31

-used to separate wavelengths in light of diffrerent substances - atomics spacing in crystals

Question 32

what is the refractive index of a material?

Answer 32

the ratio of the speed of light in a vacuum to the speed of light in that material

Question 33

what is the equation for refractive index?

Answer 33

n= c/c(subscript s)

Question 34

what is snell's law?

Answer 34

n₁sinθ=n₂sinθ

Question 35

what happens when light travels from a less optically dense medium to a more optically dense material?

Answer 35

it bends towards the normal

Question 36

what happens when light travels from a more optically dense material to a less optically dense material?

Answer 36

it bends away from the normal

Question 37

what is the equation for the critical angle?

Answer 37

sinθ=n₂/n₁ where n₁ is more optically dense that n₂

Question 38

what happens when the angle of incidence is larger or equal to the critical angle?

Answer 38

total internal reflection

Question 39

what is are the features of cladding?

Answer 39

- it has a much lower optical density meaning there is a very small critical angle

Question 40

-when does material dispersion occur? -what does this cause? -how do we solve this?

Answer 40

-when different wavelengths of light arrive at the end of fibre at different time -pulse broadening, signal degradation - use monochromatic light

Question 41

-when does modal dispersion occur? -what does this cause? -how do we solve this?

Answer 41

-when waves take different paths in the fibre meaning they arrive at the end of the fibre at different times -pulse broadening -use of monomode fibre

Question 42

-what is pulse absorption? -how to we solve this?

Answer 42

-when the signal is absorbed by the material leading to a reduction in signal amplitude -use of signal repeaters or boosters

Question 43

Why does the presence of a water droplet on a reflection tube cause a reduction in the intensity of the light?

Answer 43

it prevents total internal reflection from occurring as it increases the critical angle. causing refraction instead.

Question 44

What is the pattern produced on a screen when a light source goes through a single slit?

Answer 44

- bright and dark fringes - central fringe is significantly more intense

Question 45

how has the pattern produced changed on a screen when a light source going through a single slit is now red instead of green?

Answer 45

-fringes are further apart - wider central maximum

Question 46

Describe and explain the paths followed by red and blue rays immediately after the light is incident on a glass-liquid interface. (picture the semi-sphere with some water drops on top)

Answer 46

- Blue ray undergoes TIR - Red ray gets diffracted - this is because the critical angle for red light is greater than that of blue light

Question 47

Explain how the pattern produced on a fluorescent screen where electrons are incident on it, supports the idea that the electron beam is behaving as a wave rather than as a stream of particles

Answer 47

- Lines of bright and dark maxima, bright being constructive and dark being destructive interference -these are wave-like characteristics, similar to those on a diffraction grating - particle behaviour would only produce a small circle of light

Question 48

Explain how the pattern produced on a fluorescent screen where electrons are incident on it, supports the idea that the electron beam is behaving as particles

Answer 48

-there is light emission due to the excitation and de-excitation of electrons - this happens because of one to one interaction/ collisions this is a particle like characteristic