Refraction, Optic Fibres, Waves Review Questions with complete Solutions Graded A+
State and explain why the core of an optical fibre is made as narrow as possible. - Answers To reduce multipath dispersion
To prevent data loss from the core which would cause attenuation.
State one application of...
State and explain why the core of an optical fibre is made as narrow as possible. - Answers To reduce
multipath dispersion
To prevent data loss from the core which would cause attenuation.
State one application of optical fibres and explain how this has benefited society. - Answers Endoscope -
improved medical diagnosis
Communications -improved transmission of data/high speed internet.
what are the 3 parts of an optic fibre - Answers 1. core - central part - high constant refractive index
2. sheath - outermost layer, protection
3. cladding - low constant refractive index
purpose of cladding - Answers 1. protects outer surface of core from stretching or breakage
2. prevents loss of signal form scratches
3. provides a lower constant refractive index so TIR occurs
4. prevent crossover/cross-talk in a bundle of fibres - ensures data security
what 2 processes cause signal loss - Answers 1. dispersion - pulse broadening, pulses get wider merging
into eachother
2. attenuation - absorption and leakage of light reduce the amplitude of signals/causes power loss
what is material dispersion - Answers (chromatic dispersion)
1. violet/blue light travels more slowly than red light in glass
2. red light reaches the end before blue
3. this leads to material pulse broadening
how to reduce material dispersion - Answers 1. use monochromatic light
2. use shorter repeaters so that the pulse is reformed before significant pulse broadening has taken
place
what is multipath dispersion - Answers modal dispersion
1. light that enters the fibre at different angles has different path length through the fibre
2. light with shorter path lengths arrive before light with longer path lengths leading to pulse broadening
, how to reduce multipath dispersion - Answers 1. use mono mode or graded index fibres
2. use shorter repeaters so that the pulse is reformed before significant pulse broadening has taken
place
what do repeaters do? - Answers they restore signal quality by
1. changing the optical signal into an electrical form
2. amplify and sharpen/regenerate it
3. the convert it back into an optical signal
what is unchanged when light moves from one material to another - Answers frequency
if the refractive index is higher, how is the speed and wavelength of light different? - Answers 1. the
speed is lower and the wavelength is shorter
when light moves form a material with a high refractive index to a low refractive index, how does its
direction change - Answers it bends away form the normal (angle of refraction > angle of incidence)
what are the 2 conditions for TIR to occur? - Answers 1. the ray starts in the higher refractive index
material
2. the angle of incidence is larger than the critical angle
State what is meant by monochromatic. - Answers A single wavelength/ frequency of light
State one safety precaution that should be taken while using a laser - Answers Do not look into laser
Do not point the laser at others
Do not let (regular) reflections enter the eye
Safety signs
Suitable safety goggles
Other than electromagnetic radiation, give one example of a wave that is transverse - Answers surface
of water/water waves/in ripple tank
rope /slinky clearly qualified as transverse /
secondary waves
State one difference between a transverse wave and a longitudinal wave. - Answers Transverse wave:
oscillation (of medium) is perpendicular to wave travel
Transverse can be polarised
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