Waves

Question 1

Definition of a progressive wave

Answer 1

A wave that carries energy from one place to another without transferring any material

Question 2

What do these waves do: EM/X-ray & Gamma

Answer 2

EM - Heat
X-ray & Gamma - Ionisation

Question 3

What is a transverse wave (Give an example)

Answer 3

A wave that vibrates perpendicular to direction of travel/energy transfer (EM)

Question 4

What is a longitudinal wave (Give an example)

Answer 4

A wave that vibrates along the direction of energy transfer (Sound)

Question 5

What is a polariser

Answer 5

A filter that only transmits waves in a singular plane

Question 6

Define superposition

Answer 6

When two or more waves pass through each other

Question 7

What does constructive/destructive interference do?

Answer 7

Constructive - Bigger amplitudes
Destructive - No amplitude

Question 8

Define coherent

Answer 8

Two sources which have the same frequency & wavelength

Question 9

Define monochromatic

Answer 9

Light with a single wavelength

Question 10

What type of path difference does constructive/destructive

Answer 10

Constructive - path difference wavelength
Destructive - path difference 1/2 wavelength

Question 11

Define a stationary wave

Answer 11

Two progressive waves superpose with the same frequency & wavelength moving in opposite directions

Question 12

What is intensity, what is meant by intensity of light and what is the equation for it. Intensity for monochromatic light changes, why?

Answer 12

Intensity - Power per unit area
Intensity of light - Number of photons
Power per unit area
Changes because even though all photons are the same, there are more photons per second

Question 13

Explain diffraction pattern of white light

Answer 13

Bright central fringe
Fringes decrease in intensity
Blue (inside) to red (outside) colour spectrum

Question 14

Difference between red and blue light

Answer 14

Red - Longer wavelength
Blue - Shorter wavelength

Question 15

How does Youngs Double Slit experiment work and explain the outcome

Answer 15

Slits same size as wavelength
Two Diffractions
Fringes made of a bright point and decrease in intensity when moving to outside.

Question 16

Who were the people in different light theories and what were their theories

Answer 16

Newton - Corpuscles (particles)
Huygen - Waves

Question 17

Equation to find slit seperation

Answer 17

Area (m^3) divided b y number of slits

Question 18

What happens when light is shone through more slits

Answer 18

Interference patterns are sharper

Question 19

What is the EM spectrum, how is it classed.

Answer 19

Radio Micro Infa-red Visible Ultra Violet X-ray Gamma
Longer wavelength/Less energy ——————–> Lower wavelength/More energy

Question 20

Examples of what EM waves are used for

Answer 20

R - broadcasting M - Radar I - Radiators V - Light UV - Florescent lights X-ray - Inside viewing G - Medicine (Cancer)

Question 21

Different wavelengths for EM spectrum

Answer 21

R - 10^3
M - 10^-2
I - 10^-5
V - 10^-6
UV - 10^-8
X - 10^-10
G - 10^-12

Question 22

Different frequencies for EM spectrum

Answer 22

R - 10^4
M - 10^8
I - 10^12
V - 10^15
UV - 10^16
X - 10^18
G - 10^20

Question 23

Visible light spectrum and the wavelengths of their colours

Answer 23

Red -> Purple Longer -> Shorter wavelength
R(740-625)
O(625-590)
Y(590–565)
G(565-520)
LB(520-500)
B(500-435)
P(435-380) nano meters

Question 24

Describe the Balmer series

Answer 24

Hydrogen spectrum
P(n6-n2)
G(n5-n2)
LB(n4-n2)
R(n3-n2)

Question 25

Definition of a refractive index

Answer 25

How much light slows down in a material

Question 26

What happens to wave in refraction

Answer 26

Speed and wavelength change, frequency remains constant

Question 27

What is needed for light to refract towards normal

Answer 27

Refractive index of material 1 is smaller than material 2

Question 28

What is needed for light to refract away from the normal

Answer 28

Refractive index of material 1 is bigger than material 2 and angle of incidence is less than the critical angle

Question 29

What is needed for total internal reflection

Answer 29

Refractive index of material 1 is bigger than material 2 and angle of incidence is bigger than critical angle.

Question 30

How does a light ray travels along a boundary

Answer 30

Refractive index of material 1 is bigger than material 2 and angle of incidence is equal to the critical angle.

Question 31

What is an optical fibre

Answer 31

A thin flexible tube of glass or plastic fibre that carries signals at light at a fast speed

Question 32

What does absorption do to waves

Answer 32

The energy is lost through the material resulting in a reduced amplitude

Question 33

What are pros and cons of optical fibres

Answer 33

Pros - No signal degradation over distance/Fast/Can travel very long distances Cons - Expensive/Hard to replace

Question 34

What does the cladding of a fibre do

Answer 34

Protects the core for damage

Question 35

How does a fibre work

Answer 35

Since the refractive index of the core is bigger than the cladding, it allows TIR since the fibre is so small the rays always hit the boundary at an angle bigger than the critical angle.

Question 36

Define modal dispersion

Answer 36

Light rays take different paths and arrive at the end at different times making there signal smeared.

Question 37

How can we stop modal dispersion

Answer 37

Use a single mode fibre where light can only take one path

Question 38

Define material dispersion

Answer 38

Light has different wavelengths and speeds causing light to arrive at different times.

Question 39

How can we stop material dispersion

Answer 39

Use monochromatic light

Question 40

What is pulse broadening

Answer 40

When dispersion occurs, signals can overlap and become muddled

Question 41

How do we reduce pulse broadening

Answer 41

Use an optical fibre repeater which boosts and regenerates the signal

Question 42

What is the musical name for harmonics

Answer 42

Octaves