P2

Question 1

Fibre optics used for

Answer 1

Become a vital backbone for modern communication systems

Question 2

Refractive index

Answer 2

Of a transparent medium is the ratio or the speed of light in vacuum to its speed in the medium

Question 3

What does light travel best through

Answer 3

A vacuum

Question 4

How does light travel through a vacuum

Answer 4

Rapidly oscillating electric field generates an oscillating magnetic field, and changing magnetic field in turn generates another nearby oscillating electric field and so the wave progresses rapidly through space

Question 5

Normal line

Answer 5

A line at right angles to the surface of a transparent medium that passes through a point where a Ray enters or exits the medium. The direction of rays is always described by measuring the angle between the Ray and normal line

Question 6

Incidence

Answer 6

The direction of incoming ray

Question 7

Refraction

Answer 7

The bending of the direction of travel, so it describes the direction of an outgoing Ray after bending

Question 8

Internal reflection

Answer 8

When a wave that is already in an optically dense medium hits the boundary with a less dense medium and energy is reflected back into the denser medium

Question 9

Critical angle

Answer 9

For a Ray in a medium with. Higher refractive index hitting the boundary with a less dense medium, this is rhe angle of incidence where the refracted Ray would be at 90 degrees

Question 10

Total internal reflection

Answer 10

All the wave energy is internally reflected. None is lost as a refracted Ray. This happens for all angles of incidence larger than the critical angle

Question 11

Optical fibres

Answer 11

Long thin cylinders of glass or sometimes plastic

Question 12

What happens when light is fed into the cut end of the fibre

Answer 12

When hits the side of fibre almost does so at angles greater than the critical angle. That means all Ray of light gets totally internally reflected and keep bouncing down the length of the fibre. No wave energy gets lost through the walls of the fibre although as glass is not perfectly transparent some is gradually absorbed

Question 13

What happens when light is fed kilometres away

Answer 13

The intensity is still large enough to measure as a signal. If the joints between them qrw carefully made the optical fibres joined ends to end cam pass their light signals on to the next stage in a fibre network again with only a small loss in intensity

Question 14

Why are light in optical fibres more efficient way of transmitting signals than sending electrical impulses down copper cables

Answer 14

Copper cables suffer from quite large losses due to electrical resistance meaning that after a few hundred metres most of the signal has been attenuated away and amplifiers are needed to boost it up again

Question 15

How are optical fibres put in place

Answer 15

By installing and jointing

Question 16

Temporary jointing of optical fibre

Answer 16

Can be temporary using a proprietary connector or permanent

Question 17

How can permanent joint be achieved

Answer 17

By compression or by a welding process using heat

Question 18

What does reliability if signal transmission depend on

Answer 18

Quality of fonts between fibres, both along a cable run and also those to the optical transmitter at one end and the optical receiver at the other end

Question 19

Where do substantial losses of signal intensity occur unless the cable is damaged

Answer 19

The cable to the optical transmitter to the optical reciever

Question 20

How can the optical signal be boosted

Answer 20

Optical amplifier

Question 21

What is an optical amplifier

Answer 21

Offshoot of solid state laser technologies, they increase rhe intensity of the beam without needing to convert it back into the electrical signal

Question 22

Where are fibre optics used

Answer 22

In endoscopes

Question 23

What are endoscopes

Answer 23

Optical instruments either long tubes rhat can be inserted into a body organ through an opening such as the throat or ear.

Question 24

How is the image piped back out

Answer 24

Shorter rigid tubular endoscopes use a series of relay lenses
In longer flexible fibrescopes rhe image is also conveyed by a second fibre bundle back to an eyepiece or camera lens

Question 25

Each fibre in the bundle is as thin as human hair and consists of?

Answer 25

A core, cladding and a protective plastic buffer coating

Question 26

How many pixels of light does fibre transmit

Answer 26

One
Therefore resolution depends in how many fibres are in the bundle

Question 27

Where are fibre bundles protected

Answer 27

Inside the endoscopes long, flexible insertion tube

Question 28

What does insertion tube also carry as well as fibres

Answer 28

Also carries control lines that can move the bending section of the distal end
Which is where the fibres terminate and interference with the lenses, one to distribute rhe incoming light and other to focus the image

Question 29

Analogue signal

Answer 29

The info transferred by each fibre of an endoscope

Question 30

Examples of an analogue signal

Answer 30

Electricla signal made by a microphone which mimics the shape and intensity of the sound waves they are detecting
Position of the pointer on a pressure dial gauge

Question 31

The light travelling down rhe fibre has a what

Answer 31

High frequency wave

Question 32

Digital signal

Answer 32

Conveys in binary code a number thay represents the size of the measured quantity

Question 33

How can a huge amount ot digital data be transmitted in a short time

Answer 33

As high frequency waves are being used

Question 34

By digitising information whay does this do

Answer 34

Able to send more data faster than analogue transmission and also makes the transmission much more reliable and interference fee
Even though digital bursts you can still reliable ready whether ir is on or off

Question 35

How do u convert signals from analogue to digital

Answer 35

Using an analogue to digital converter

Question 36

How does the converter work

Answer 36

At regular intervals this device samples measures the size of analogue signal
Each sample value is measure and converted into a whole number of units

Question 37

Whay base does binary code use

Answer 37

Base 2 which represents any number as a series of ones and zeros
On equals one
And off equals to zero

Question 38

1st step analogue to digital conversion

Answer 38

Select a transducer a device that produces an analogue electrical voltage signal proportional to the quantity you want to measure, for example a pressure sensor, a thermocouple for thermistor for temperature a microphone for sound

Question 39

Step 2 of cinversion

Answer 39

Connect the output of the transducer to the input of an a to d converter, using a screened cable. To avoid picking up electrical interference the screening must be well earthed

Question 40

Step 3 of conversion

Answer 40

Set up the a to d converter to sample the analogue signal
This is equivalent to taking measurements to plot results out on a voltage time graph

Question 41

4th step to conversion

Answer 41

Select an appropriate sampling rate, which is your sensitivity on the time axis

Question 42

5th step to conversion

Answer 42

Select an appropriate sensitivity got the conversion of the voltage single into a number. The smallest difference you will be able to convey with the digitally converted data is one unit

Question 43

6th into conversion

Answer 43

Connect the a to the d converter output to a switch transmittervto send the digital information either electronically down copper cables tirelessly using Bluetooth WiFi or similiar protocols or by optical signals along a fibre netwrom

Question 44

Boradvand

Answer 44

Term to indicate the speed and carrying capacity of a data channel.

Question 45

Multimodefibre

Answer 45

Standard fibre cable used for sending optical signals over short to medium distances
E.g connections to instruments
Optical fibres are around 100um

Question 46

Single mode fibre

Answer 46

Even narrower core 8-10um
Less than ten wavelengths of the infrared light that is used in them
This means there is no space for different beams travelling at different angles down the core
Light waved move down the centre of the fibre and all the signal energy reaches the far end of the fibre

Question 47

Inverse Square law for intensity of wave equation

Answer 47

I=k divided by rsquared