Waves - The better set of flashcards

Question 1

How does TIR transmit information along an optic fibre?

Answer 1

light fibre consists of core and cladding with a lower refractive index or optical density. Light is incident at an angle greater than the critical angle which results in TIR.

Question 2

What happens to the wavelength, frequency and speed of light when a ray of light travels from air into glass?

Answer 2

Wavelength = decreases 
Frequency = stays the same
Speed = decreases

Question 3

Equation to find out diffracted angles?

Answer 3

N1SINX1 = N2SINX2

Question 4

State the purpose of the outer sheath in an optical fibre?

Answer 4

Prevent physical damage to the fibre and strengthen it.

Question 5

Describe the structure of step-index optical fibres outlining the purpose of the core and the classing?

Answer 5

Core is transmission medium for EM waves to progress by total internal reflection, the cladding provides a lower refractive indies to ensure TIR occurs and offered protection of boundary from scratching which could lead to light leaving the core.

Question 6

What is a longitudinal wave?

Answer 6

A wave with parallel oscillations - sound waves and P waves

Question 7

What is a transverse wave?

Answer 7

A wave with perpendicular oscillations and it can be polarised! such as electromagnetic waves and S waves

Question 8

Use wave theory to explain how a pattern of bright and dark patches are formed…

Answer 8

Slits act as coherent sources (1) waves diffract at the slits (1) the waves superpose (1) and bright patches are the constructive interference (1) whilst the dark patches are destructive interference (1)

Question 9

What is monochromatic light?

Answer 9

Light of a single wavelength

Question 10

How is a stationary wave formed?

Answer 10

The result of the interference of the two waves above is a new wave pattern known as a standing wave pattern. Stationary waves are produced whenever two waves of identical frequency interfere with one another while traveling opposite directions along the same medium Nodes are produced when crest meets tough and antinodes are produced when a crest+crest or trough+trough

Question 11

Explain how Young’s interference fringes are formed and why the first slit should be narrow and why the second slits should be coherent.

Answer 11

A narrower slot gives wide diffraction which will ensure that the second slits are illuminated. A narrow first slit also provides coherent light sources so the second slits are illuminated by the same source giving the same wavelength. Constructive and destructive interference occurs.

Question 12

Properties of a laser light:

Answer 12

Monochromatic (waves of single wavelength)
Collimated (produces an appromixmately parallel beam)
Coherent (waves produced in constant phase)
Polarised (vibrations in one plane only)

Question 13

Displacement

Answer 13

The distance and direction of a particle from equilibrium position.

Question 14

Amplitude

Answer 14

Maximum displacement of a vibrating particle

Question 15

Wavelength

Answer 15

Shortest distance between two particles in phase

Question 16

Frequency

Answer 16

Number of wave cycles occurring each second

Question 17

Wavespeed

Answer 17

Distance travelled by a wave each second

Question 18

Phase difference

Answer 18

Measured in degrees or radians ( the amount by which one wave lags behind another wave)

Question 19

Path difference

Answer 19

The differences in lengths of 2 waves

Question 20

Progressive waves

Answer 20

Waves whose oscillations travel and transfer energy.

Question 21

Give an example of how polarisation can be used

Answer 21

Polarisation can be used in things such as Polaroid sunglasses to reduce glare or in a camera to enhance an image

Question 22

what is superposition?

Answer 22

The point where waves meet - the total displacement at a point is equal to the sum of the individual displacements at that point

Question 23

Is energy transferred in stationary waves

Answer 23

No

Question 24

What is diffraction?

Answer 24

Is the spreading out of waves when they pass through a gap or over an edge - increasing the lit width creates an intense but narrow central maximum and vice Verda

Question 25

In diffraction gratings…

Answer 25

The more slits, the sharper the interference pattern. Constructive interference patterns are called maxima

Question 26

N = C1/C2

Answer 26

The absolute refractive index of a material measured by how much it slows down light and is a ratio.

Question 27

What must happen for TIR to occur?

Answer 27

The light must travel form a more optically dense medium to a less optically dense medium. The angle of incidence of the light ray must exceed the critical angle of the interference

Question 28

Step- index optical fibres…

Answer 28

Core = high refractive index (more dense)
Cladding = pow refractive index (less dense)

Question 29

What is modal dispersion?

Answer 29

Some rays take longer to get to the receiver based on the path they take.

Question 30

What is material dispersion?

Answer 30

Different frequencies travel at different speeds in the core which means they reach the receiver at different times.