Waves

Question 1

speed of light

Answer 1

c = 3 x 10^8 m/s

Question 2

speed of sound

Answer 2

343 m/s

Question 3

wavelength frequency speed

Answer 3

v = fλ

Question 4

frequency, time period

Answer 4

T = 1/f

Question 5

Polarization

Answer 5

waves of the transverse waves are limited to one plane of movement, while the rest is absorbed

Question 6

polarising filters what they do

Answer 6

only waves oscillating in same direction as filter will pass through
2 filters perpendicular to each other won’t let through any light

Question 7

uses of polarisation

Answer 7

• polarised sunglasses to reduce glare
• receiving areal and radio signals

Question 8

stationary waves nodes and antinodes

Answer 8

node - no displacement
anti-node - point of max displacement

Question 9

distance between two nodes

Answer 9

1/2 λ

Question 10

Explain how standing wave is formed (3)

Answer 10

• superposition
• two waves of same frequency and amplitude
• travelling in opposite directions
• one is reflected

Question 11

points between two nodes

Answer 11

points between two nodes all in phase

Question 12

For first harmonic:
frequency, length, tension, μ

Answer 12

For first harmonic:
f = 1/2L sqrt(T/μ)

where μ is mass/length of string

Question 13

standing wave with microwave practical setup

Answer 13

transmitter
metallic reflective plate 1/2λ away
movable detector in middle

when detector is at plate, min
when at middle, max

Question 14

standing wave in a tube

Answer 14

at closed end: pressure antinode, displacement node

at open end: pressure node, displacement antinode

Question 15

laser

Answer 15

monochromatic light (one wavelength) so light is coherent

Question 16

double slit setup and result

Answer 16

laser which has similar wavelength to gap

result is equally spaces fringes

Question 17

single slit diffraction monochromatic

Answer 17

large central maxima with smaller less intense fringes on either side

Question 18

single slit diffraction white light

Answer 18

• central maxima bright white
• less wide less intense fringes on either side
• fringes on either side would be spectrum which get more and more spread out
• violet closest to maxima, red furthest

Question 19

diffraction

Answer 19

the spreading out of waves as they pass through a gap or around an obstruction

Question 20

single slit equation (destructive min)

Answer 20

dsin(θ) = mλ

where d is the slit width
m is the order of the min

Question 21

double slit equation

Answer 21

W = λD/s

where w is fringe spacing
D is from slits to screen
s is slit spacing

Question 22

diffraction grating equation and derivation

Answer 22

dsin(θ) = nλ

where d is the slit width
n is the order of the bright spot

derive on paper

Question 23

snells law

Answer 23

n1sin(θ1) = n2sin( θ2)

Question 24

refractive index, speed of light

Answer 24

n = c in air/ c in material

Question 25

critical angle

Answer 25

angle of incidence when angle of refraction = 90
above which total internal refraction happens

Question 26

show c, n1, n2 equation

Answer 26

n1 sin θ1 = n2 sin θ2
n1 sin θc = n2

sin θc = n2/n1

Question 27

uses of total internal reflection

Answer 27

optic fibres

Question 28

step index optic fibre

Answer 28

the refractive index of each component increases moving from the outside to the centre of the fibre

Question 29

role of cladding in optic fibre

Answer 29

• Protect the thin core from damage and scratching
• Prevent signal degradation through light escaping the core, which can cause information from the signal to be lost
• It keeps the core separate from other fibres preventing information crossover

Question 30

prisms

Answer 30

prisms will always totally internally reflect

Question 31

approx λ for em waves

Answer 31

Radio waves - 1km
Microwaves - 10 cm
Infrared - 10^-5
Visible - 10^-6
Ultraviolet - 10^-8
X rays - 10^-10
Gamma - 10^-12

Question 32

coherent (waves)

Answer 32

have same wavelength, frequency and are in phase

Question 33

stationary wave experiment

Answer 33

• signal generator connected to vibration transducer
• string going across a pulley at end of bench with a mass hung on one end
• measure mass and length of string to find μ
• find tension
• vary frequency of signal generator until first harmonic
  equation

Question 34

2 reasons for signal degradation and effects on signal

Answer 34

• absorption by material causes loss in amplitude
• dispersion causes broadening

Question 35

Two types of dispersion (signal degredation)

Answer 35

• modal - light enters at different angles
• material - not all light had same wavelengths

Question 36

diffraction grating limitations (from equation)

Answer 36

d sin(θ) = nλ
sin(θ) can’t be greater than 1
so only certain values of n order possible