EM spectrum and fibre optics

Question 1

what different types of waves do you know?

Answer 1

transverse and longitudanal

longitudanal:
particles vibtrate forwards and back as they travel forward e.g sound waves

transverse:
partcles travel up and down in a sine wave pattern as they move forward e.g,. EM Radiation

Question 2

tell me about the EM radiation..

Answer 2

EM radiation is a spectrum of radiation that can act as both a wave and particle

transverse waves characterised by frequency and wavelength.
consists of 7 categories ranging from low energy low frequency to high energy high frequency wavelength

radio - long wavelength, low freq, low energy
micro
infrared
visible
UV
xrays
gamma rays - short wavelength , high enery

Question 3

which EM waves are ionising

Answer 3

UV, Xrays, Gamma
have enough energy to be ionising

Question 4

define frequency and amplitude and wavelength of a wave

Answer 4

frequency - number of full wave cycles per second

wavelength - the distance from one point of the wave to the same point on the next wave e.g. peak to peak

amplitude - the max displacment of a wave from its mean position

Question 5

is light a particle or a wave?

Answer 5

both
acts as discrete particles of energy e.g. photons
but also as a wave e.g. can be refracted and reflected.

e.g. described as photons in LASER but a wave for fibreoptics

Question 6

what is the speed of EM radiation in a vaccum?

Answer 6

same as speed of light = 2.98x 10^8 m/s

Question 7

what equation can be used to calculate speed of a wave?

Answer 7

speed = wavelength x frequency

v = velocity
f= frequency
lambda = wavelength

the speed remains constant and thus freq and wavelength are inversely proportional

Question 8

how is the energy of a wave calculated?

Answer 8

E=h x f

f = frequency
h= planks constant - the energy of one photon of EM radiation of a particular frequency. e.g. gamma rays would be more than visible light
E = energy

Question 9

what is the wavelength of visible light?

Answer 9

400-700nm
blue to red

Question 10

can you list some uses of EM radiation in hospitals..

Answer 10

radio - communication
microwaves - food
infrared - gas analysis
visible light - endoscopes, microscopes
UV light - therapy for skin disorders e.g. psoriasis
Xray - imaging and diagnosis
gamma rays - radiotherapy

Question 11

what type of light does the pulse oximeter use?

Answer 11

660nm - red light visible
940nm - infrared - longer wavelength

Question 12

what is reflection?

Answer 12

when light hits a reflective surface, the wave bounces back towards itself but at an angle.
this angle depends on the angle that it hit the surface.

angle of incidence = angle of reflection

Question 13

what is refraction?

Answer 13

When light passes from one medium to another, the direction it is travelling changes by a specific angle i.e. it bends.

This is because light has different speeds in different mediums.

The level and direction of refraction depends on the properties of both mediums and the angle of incidence.

The refractive index is measure of how much light slows down in a medium compared to that in a vacuum.
e.g. index of refraction of air = 1 , glass =1.5

when light travels from medium that is more dense to less dense, it will bend away from the normal line. and vice versa if travelling from less to more dense.

angle of incidence = that angle from light in first medium
angle of refraction = in new medium

(more dense, more stuff to push it toward the normal)

Question 14

what is meant by total internal reflection?

Answer 14

when light is moving from a more dense to less dense medium e.g. glass to air
as angle of incidence increases, the angle of refraction increases away from normal.
eventually this will reach 90 degrees. the angle of incidence that does this is called the critical angle

beyond the critical angle, light will be reflected back into the same medium

Question 15

what is the critical angle

Answer 15

the angle of incidnece that causes light to refract by 90 degrees

Question 16

what is Snell’s law?

Answer 16

equation to predict the angle of refraction based on the refractive indices of each medium AND the angle of incidence.

Question 17

what is meant by diffraction

Answer 17

the spread of light waves as they pass through a gap

the extent of this spreading depends on the wavelength of light compared to the gap size

Question 18

how does a prism work?

Answer 18

when light comes from one medium to another, it changes speed

white light contains polychromatic light of different wavelengths.

each wavelength is affected differently by the change in medium / speed so it is separated into its different colours which travel at slightly different angles.

Question 19

what is a fibreoptic scope?

Answer 19

A fibreoptic scope is a piece of equiptment used to visualise images by the use of light and total internal reflection e.g. fibreoptic larygnoscopes

it consists of thousands of glass fibres arranged in a coherent and highly ordered fashion to transmit light from source to distant target.

Question 20

describe how a fibreoptic scope works?

Answer 20

work by the principle of total internal reflection

1. consist of many glass fibres surrounded in cladding glass.
2. light source is used to illuminate the object visualised e.g. cords
3. light bounces off this and light travels in glass fibres
4. light hits the cladding glass medium (lower refractive index) and is reflected back into the fibres. this is because the angle of incidence is bigger than critical angle and thus total internal reflection is seen.
5. thousands of glass fibres are arranged in parrallel and doing the same thing.
6. therefore the image is transmitted as many beams of parrallel light without loss of energy. each fibre produces 1 pixel on the image.
7. at the eyepiece the image is projected as light escapes

each fibre is 8-10um thick and around 15000 fibres
there is a control lever that can move the tip and direct the angle of light.
often also have a suction port

Question 21

what are the uses of fibreoptics?

Answer 21

airway
* laryngoscopes - difficult airway & awake intubation, guiding of a percutaneous trachy, diagnosis of upper airway pathology, pulmonary suctioning under direct vision

endoscopy - sigmoidoscopy and upper GI

Question 22

what are the pros and cons of fibre optics

Answer 22

pros - can list all the uses. uses light - relatively simple technology but produces v. high quality images. quick and can transmit over long distance hence can view areas not possible to view normally. use of light rather than electricity means they are less at risk of interference

cons - expensive, the fibres must be perfectly alligned to prevent distortion of the image. need skilled technician. blood / secretions can obstruct view. may completely obstruct a partially obstructed airway.

Question 23

give examples of fibreoptic scopes you know?

Answer 23

fibreoptic bronchoscope

ambuscope - disposable fibreoptic bronchoscope. reduces risk of infection and doesnt need sterilisation. howeever no suction port

optical stylet - rigid steel tube with fibreoptics inside. use direct laryngoscopy technique which is more familiar however less able to steer around obstruction