Physicis Flashcards
What occurs in refraction
The angle of incidence is smaller than the angle of refraction
Material light passes through
Medium
Refraction along the boundary occurs
Incident angle is equal to the critical angle
Total internal reflection occurs
Incidence angle is bigger than the critical mass
Medical endoscopy
Medical Endoscopes
• The endoscope consists of a
bundle fibres in a tube. More
expensive instruments have more
fibres = clearer image.
• Some of the fibres are used to
transmit light into the body
• The image transmitted is
pixelated, since each fibre
transmits one pixel of coloured
Features of optical fibres
Optical fibres are thin strands of solid glass
which are widely used in communication,
medicine, lighting and as sensors.
They exploit total internal reflection in order to
carry beams of light over long distances and
along winding paths.
The glass core is often encased
in a layer of cladding, which
prevents light escaping the
core. A protective plastic jacket
Fiver optics and copper cable
Fibre optics
Copper cable
• More efficient
• Very little loss of wave energy
• Requires no amplifier
• Cheaper to produce
• Lightweight (good for using in
aircraft)
• Can carry more information
• Less efficient
• Large losses of energy due to
electrical resistance
• Requires an amplifier every few
hundred meters to boost the
signal u
How they carry signals
All rays of light are totally internally reflected.
• No wave energy gets lost through the walls of the fibre, although as
the glass is not 100% transparent, some of it is gradually absorbed.
• When the light reaches the end of the fibre, several kilometres away
the intensity is still large enough to measure a signal.
• If the joints between them are made carefully enough, optical fibres
can pass their signals on to the next stage in the fibre network, with
little loss to intensity.
Using fibres to carry signals
• Installing optical fibres requires specially trained
technicians, with the right tools and equipment.
• The jointing can be permanent or temporary.
• The reliability of the signal transmission depends on the
quality of joints between fibres, both along the cable run
and also those to the optical transmitter (an LED or Laser) at
one end at the optical receiver at the other.
• These are the only places where substantial loss of signal
can occur, unless the cable is damaged.
• Signal is gradually lost over the length of the cable, but after
several Km there is still enough (1%) to be boosted by an
optical amplifier.
• These increase the intensity of the light without needing to
convert it back into an electrical signal.
Reflected
R e f r a c t e d
Digital signal
Are discrete time signals
generated by digital
modulation.
• Has only two values 0 or 1
Analogue
Continous signal
Infinite values
What are diffraction gratings?
Optical components with an array of parallel lines or slits.
What effect do diffraction gratings have on incoming waves of light?
They cause the waves to divide and diffract in various directions.
What is the grating constant?
The distance between adjacent slits or lines in a diffraction grating.
What happens to light waves when they strike a grating?
They are diffracted into several paths or orders.
What is produced as a result of diffraction?
A spectrum, a band of colours spread out like a rainbow.
What factors affect the angles of the spectra produced by diffraction gratings?
The grating constant and the wavelength of light incident on the grating.
What occurs during constructive interference in diffraction?
Light waves diffract in such a way that they align peak to peak, producing bright, colourful lines.
Fill in the blank: The angles of the spectra are shifted depending on the _______ and the wavelength of light.
grating constant
